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chromium / external / github.com / WebKit / webkit / efb9667cfbcf8cb9e447d178761066039bfea942 / . / Source / JavaScriptCore / b3 / B3ReduceStrength.cpp
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/*
* Copyright (C) 2015-2020 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "B3ReduceStrength.h"
#if ENABLE(B3_JIT)
#include "B3AtomicValue.h"
#include "B3BasicBlockInlines.h"
#include "B3BlockInsertionSet.h"
#include "B3ComputeDivisionMagic.h"
#include "B3EliminateDeadCode.h"
#include "B3InsertionSetInlines.h"
#include "B3PhaseScope.h"
#include "B3PhiChildren.h"
#include "B3ProcedureInlines.h"
#include "B3PureCSE.h"
#include "B3UpsilonValue.h"
#include "B3ValueKeyInlines.h"
#include "B3ValueInlines.h"
#include <wtf/HashMap.h>
#include <wtf/MathExtras.h>
#include <wtf/StdLibExtras.h>
namespace JSC { namespace B3 {
namespace {
// The goal of this phase is to:
//
// - Replace operations with less expensive variants. This includes constant folding and classic
// strength reductions like turning Mul(x, 1 << k) into Shl(x, k).
//
// - Reassociate constant operations. For example, Load(Add(x, c)) is turned into Load(x, offset = c)
// and Add(Add(x, c), d) is turned into Add(x, c + d).
//
// - Canonicalize operations. There are some cases where it's not at all obvious which kind of
// operation is less expensive, but it's useful for subsequent phases - particularly LowerToAir -
// to have only one way of representing things.
//
// This phase runs to fixpoint. Therefore, the canonicalizations must be designed to be monotonic.
// For example, if we had a canonicalization that said that Add(x, -c) should be Sub(x, c) and
// another canonicalization that said that Sub(x, d) should be Add(x, -d), then this phase would end
// up running forever. We don't want that.
//
// Therefore, we need to prioritize certain canonical forms over others. Naively, we want strength
// reduction to reduce the number of values, and so a form involving fewer total values is more
// canonical. But we might break this, for example when reducing strength of Mul(x, 9). This could be
// better written as Add(Shl(x, 3), x), which also happens to be representable using a single
// instruction on x86.
//
// Here are some of the rules we have:
//
// Canonical form of logical not: BitXor(value, 1). We may have to avoid using this form if we don't
// know for sure that 'value' is 0-or-1 (i.e. returnsBool). In that case we fall back on
// Equal(value, 0).
//
// Canonical form of commutative operations: if the operation involves a constant, the constant must
// come second. Add(x, constant) is canonical, while Add(constant, x) is not. If there are no
// constants then the canonical form involves the lower-indexed value first. Given Add(x, y), it's
// canonical if x->index() <= y->index().
namespace B3ReduceStrengthInternal {
static constexpr bool verbose = false;
}
// FIXME: This IntRange stuff should be refactored into a general constant propagator. It's weird
// that it's just sitting here in this file.
class IntRange {
public:
IntRange()
{
}
IntRange(int64_t min, int64_t max)
: m_min(min)
, m_max(max)
{
}
template<typename T>
static IntRange top()
{
return IntRange(std::numeric_limits<T>::min(), std::numeric_limits<T>::max());
}
static IntRange top(Type type)
{
switch (type.kind()) {
case Int32:
return top<int32_t>();
case Int64:
return top<int64_t>();
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
template<typename T>
static IntRange rangeForMask(T mask)
{
if (!(mask + 1))
return top<T>();
if (mask < 0)
return IntRange(INT_MIN & mask, mask & INT_MAX);
return IntRange(0, mask);
}
static IntRange rangeForMask(int64_t mask, Type type)
{
switch (type.kind()) {
case Int32:
return rangeForMask<int32_t>(static_cast<int32_t>(mask));
case Int64:
return rangeForMask<int64_t>(mask);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
template<typename T>
static IntRange rangeForZShr(int32_t shiftAmount)
{
typename std::make_unsigned<T>::type mask = 0;
mask--;
mask >>= shiftAmount;
return rangeForMask<T>(static_cast<T>(mask));
}
static IntRange rangeForZShr(int32_t shiftAmount, Type type)
{
switch (type.kind()) {
case Int32:
return rangeForZShr<int32_t>(shiftAmount);
case Int64:
return rangeForZShr<int64_t>(shiftAmount);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
int64_t min() const { return m_min; }
int64_t max() const { return m_max; }
void dump(PrintStream& out) const
{
out.print("[", m_min, ",", m_max, "]");
}
template<typename T>
bool couldOverflowAdd(const IntRange& other)
{
return sumOverflows<T>(m_min, other.m_min)
|| sumOverflows<T>(m_min, other.m_max)
|| sumOverflows<T>(m_max, other.m_min)
|| sumOverflows<T>(m_max, other.m_max);
}
bool couldOverflowAdd(const IntRange& other, Type type)
{
switch (type.kind()) {
case Int32:
return couldOverflowAdd<int32_t>(other);
case Int64:
return couldOverflowAdd<int64_t>(other);
default:
return true;
}
}
template<typename T>
bool couldOverflowSub(const IntRange& other)
{
return differenceOverflows<T>(m_min, other.m_min)
|| differenceOverflows<T>(m_min, other.m_max)
|| differenceOverflows<T>(m_max, other.m_min)
|| differenceOverflows<T>(m_max, other.m_max);
}
bool couldOverflowSub(const IntRange& other, Type type)
{
switch (type.kind()) {
case Int32:
return couldOverflowSub<int32_t>(other);
case Int64:
return couldOverflowSub<int64_t>(other);
default:
return true;
}
}
template<typename T>
bool couldOverflowMul(const IntRange& other)
{
return productOverflows<T>(m_min, other.m_min)
|| productOverflows<T>(m_min, other.m_max)
|| productOverflows<T>(m_max, other.m_min)
|| productOverflows<T>(m_max, other.m_max);
}
bool couldOverflowMul(const IntRange& other, Type type)
{
switch (type.kind()) {
case Int32:
return couldOverflowMul<int32_t>(other);
case Int64:
return couldOverflowMul<int64_t>(other);
default:
return true;
}
}
template<typename T>
IntRange shl(int32_t shiftAmount)
{
T newMin = static_cast<T>(m_min) << static_cast<T>(shiftAmount);
T newMax = static_cast<T>(m_max) << static_cast<T>(shiftAmount);
if (((newMin >> shiftAmount) != static_cast<T>(m_min))
|| ((newMax >> shiftAmount) != static_cast<T>(m_max))) {
newMin = std::numeric_limits<T>::min();
newMax = std::numeric_limits<T>::max();
}
return IntRange(newMin, newMax);
}
IntRange shl(int32_t shiftAmount, Type type)
{
switch (type.kind()) {
case Int32:
return shl<int32_t>(shiftAmount);
case Int64:
return shl<int64_t>(shiftAmount);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
template<typename T>
IntRange sShr(int32_t shiftAmount)
{
T newMin = static_cast<T>(m_min) >> static_cast<T>(shiftAmount);
T newMax = static_cast<T>(m_max) >> static_cast<T>(shiftAmount);
return IntRange(newMin, newMax);
}
IntRange sShr(int32_t shiftAmount, Type type)
{
switch (type.kind()) {
case Int32:
return sShr<int32_t>(shiftAmount);
case Int64:
return sShr<int64_t>(shiftAmount);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
template<typename T>
IntRange zShr(int32_t shiftAmount)
{
// This is an awkward corner case for all of the other logic.
if (!shiftAmount)
return *this;
// If the input range may be negative, then all we can say about the output range is that it
// will be masked. That's because -1 right shifted just produces that mask.
if (m_min < 0)
return rangeForZShr<T>(shiftAmount);
// If the input range is non-negative, then this just brings the range closer to zero.
typedef typename std::make_unsigned<T>::type UnsignedT;
UnsignedT newMin = static_cast<UnsignedT>(m_min) >> static_cast<UnsignedT>(shiftAmount);
UnsignedT newMax = static_cast<UnsignedT>(m_max) >> static_cast<UnsignedT>(shiftAmount);
return IntRange(newMin, newMax);
}
IntRange zShr(int32_t shiftAmount, Type type)
{
switch (type.kind()) {
case Int32:
return zShr<int32_t>(shiftAmount);
case Int64:
return zShr<int64_t>(shiftAmount);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
template<typename T>
IntRange add(const IntRange& other)
{
if (couldOverflowAdd<T>(other))
return top<T>();
return IntRange(m_min + other.m_min, m_max + other.m_max);
}
IntRange add(const IntRange& other, Type type)
{
switch (type.kind()) {
case Int32:
return add<int32_t>(other);
case Int64:
return add<int64_t>(other);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
template<typename T>
IntRange sub(const IntRange& other)
{
if (couldOverflowSub<T>(other))
return top<T>();
return IntRange(m_min - other.m_max, m_max - other.m_min);
}
IntRange sub(const IntRange& other, Type type)
{
switch (type.kind()) {
case Int32:
return sub<int32_t>(other);
case Int64:
return sub<int64_t>(other);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
template<typename T>
IntRange mul(const IntRange& other)
{
if (couldOverflowMul<T>(other))
return top<T>();
return IntRange(
std::min(
std::min(m_min * other.m_min, m_min * other.m_max),
std::min(m_max * other.m_min, m_max * other.m_max)),
std::max(
std::max(m_min * other.m_min, m_min * other.m_max),
std::max(m_max * other.m_min, m_max * other.m_max)));
}
IntRange mul(const IntRange& other, Type type)
{
switch (type.kind()) {
case Int32:
return mul<int32_t>(other);
case Int64:
return mul<int64_t>(other);
default:
RELEASE_ASSERT_NOT_REACHED();
return IntRange();
}
}
IntRange zExt32()
{
ASSERT(m_min >= INT32_MIN);
ASSERT(m_max <= INT32_MAX);
int32_t min = m_min;
int32_t max = m_max;
return IntRange(static_cast<uint64_t>(static_cast<uint32_t>(min)), static_cast<uint64_t>(static_cast<uint32_t>(max)));
}
private:
int64_t m_min { 0 };
int64_t m_max { 0 };
};
class ReduceStrength {
public:
ReduceStrength(Procedure& proc)
: m_proc(proc)
, m_insertionSet(proc)
, m_blockInsertionSet(proc)
, m_root(proc.at(0))
{
}
bool run()
{
bool result = false;
bool first = true;
unsigned index = 0;
do {
m_changed = false;
m_changedCFG = false;
++index;
if (first)
first = false;
else if (B3ReduceStrengthInternal::verbose) {
dataLog("B3 after iteration #", index - 1, " of reduceStrength:\n");
dataLog(m_proc);
}
simplifyCFG();
if (m_changedCFG) {
m_proc.resetReachability();
m_proc.invalidateCFG();
m_changed = true;
}
// We definitely want to do DCE before we do CSE so that we don't hoist things. For
// example:
//
// @dead = Mul(@a, @b)
// ... lots of control flow and stuff
// @thing = Mul(@a, @b)
//
// If we do CSE before DCE, we will remove @thing and keep @dead. Effectively, we will
// "hoist" @thing. On the other hand, if we run DCE before CSE, we will kill @dead and
// keep @thing. That's better, since we usually want things to stay wherever the client
// put them. We're not actually smart enough to move things around at random.
m_changed |= eliminateDeadCodeImpl(m_proc);
m_valueForConstant.clear();
simplifySSA();
if (m_proc.optLevel() >= 2) {
m_proc.resetValueOwners();
m_dominators = &m_proc.dominators(); // Recompute if necessary.
m_pureCSE.clear();
}
for (BasicBlock* block : m_proc.blocksInPreOrder()) {
m_block = block;
for (m_index = 0; m_index < block->size(); ++m_index) {
if (B3ReduceStrengthInternal::verbose) {
dataLog(
"Looking at ", *block, " #", m_index, ": ",
deepDump(m_proc, block->at(m_index)), "\n");
}
m_value = m_block->at(m_index);
m_value->performSubstitution();
reduceValueStrength();
if (m_proc.optLevel() >= 2)
replaceIfRedundant();
}
m_insertionSet.execute(m_block);
}
m_changedCFG |= m_blockInsertionSet.execute();
handleChangedCFGIfNecessary();
result |= m_changed;
} while (m_changed && m_proc.optLevel() >= 2);
if (m_proc.optLevel() < 2) {
m_changedCFG = false;
simplifyCFG();
handleChangedCFGIfNecessary();
}
return result;
}
private:
void reduceValueStrength()
{
switch (m_value->opcode()) {
case Opaque:
// Turn this: Opaque(Opaque(value))
// Into this: Opaque(value)
if (m_value->child(0)->opcode() == Opaque) {
replaceWithIdentity(m_value->child(0));
break;
}
break;
case Add:
handleCommutativity();
if (m_value->child(0)->opcode() == Add && m_value->isInteger()) {
// Turn this: Add(Add(value, constant1), constant2)
// Into this: Add(value, constant1 + constant2)
Value* newSum = m_value->child(1)->addConstant(m_proc, m_value->child(0)->child(1));
if (newSum) {
m_insertionSet.insertValue(m_index, newSum);
m_value->child(0) = m_value->child(0)->child(0);
m_value->child(1) = newSum;
m_changed = true;
break;
}
// Turn this: Add(Add(value, constant), otherValue)
// Into this: Add(Add(value, otherValue), constant)
if (!m_value->child(1)->hasInt() && m_value->child(0)->child(1)->hasInt()) {
Value* value = m_value->child(0)->child(0);
Value* constant = m_value->child(0)->child(1);
Value* otherValue = m_value->child(1);
// This could create duplicate code if Add(value, constant) is used elsewhere.
// However, we already model adding a constant as if it was free in other places
// so let's just roll with it. The alternative would mean having to do good use
// counts, which reduceStrength() currently doesn't have.
m_value->child(0) =
m_insertionSet.insert<Value>(
m_index, Add, m_value->origin(), value, otherValue);
m_value->child(1) = constant;
m_changed = true;
break;
}
}
// Turn this: Add(otherValue, Add(value, constant))
// Into this: Add(Add(value, otherValue), constant)
if (m_value->isInteger()
&& !m_value->child(0)->hasInt()
&& m_value->child(1)->opcode() == Add
&& m_value->child(1)->child(1)->hasInt()) {
Value* value = m_value->child(1)->child(0);
Value* constant = m_value->child(1)->child(1);
Value* otherValue = m_value->child(0);
// This creates a duplicate add. That's dangerous but probably fine, see above.
m_value->child(0) =
m_insertionSet.insert<Value>(
m_index, Add, m_value->origin(), value, otherValue);
m_value->child(1) = constant;
m_changed = true;
break;
}
// Turn this: Add(constant1, constant2)
// Into this: constant1 + constant2
if (Value* constantAdd = m_value->child(0)->addConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constantAdd);
break;
}
// Turn this: Integer Add(value, value)
// Into this: Shl(value, 1)
// This is a useful canonicalization. It's not meant to be a strength reduction.
if (m_value->isInteger() && m_value->child(0) == m_value->child(1)) {
replaceWithNewValue(
m_proc.add<Value>(
Shl, m_value->origin(), m_value->child(0),
m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), 1)));
break;
}
// Turn this: Add(value, zero)
// Into an Identity.
//
// Addition is subtle with doubles. Zero is not the neutral value, negative zero is:
// 0 + 0 = 0
// 0 + -0 = 0
// -0 + 0 = 0
// -0 + -0 = -0
if (m_value->child(1)->isInt(0) || m_value->child(1)->isNegativeZero()) {
replaceWithIdentity(m_value->child(0));
break;
}
if (m_value->isInteger()) {
// Turn this: Integer Add(value, Neg(otherValue))
// Into this: Sub(value, otherValue)
if (m_value->child(1)->opcode() == Neg) {
replaceWithNew<Value>(Sub, m_value->origin(), m_value->child(0), m_value->child(1)->child(0));
break;
}
// Turn this: Integer Add(Neg(value), otherValue)
// Into this: Sub(otherValue, value)
if (m_value->child(0)->opcode() == Neg) {
replaceWithNew<Value>(Sub, m_value->origin(), m_value->child(1), m_value->child(0)->child(0));
break;
}
// Turn this: Integer Add(Sub(0, value), -1)
// Into this: BitXor(value, -1)
if (m_value->child(0)->opcode() == Sub
&& m_value->child(1)->isInt(-1)
&& m_value->child(0)->child(0)->isInt(0)) {
replaceWithNew<Value>(BitXor, m_value->origin(), m_value->child(0)->child(1), m_value->child(1));
break;
}
if (handleMulDistributivity())
break;
}
break;
case Sub:
// Turn this: Sub(BitXor(BitAnd(value, mask1), mask2), mask2)
// Into this: SShr(Shl(value, amount), amount)
// Conditions:
// 1. mask1 = (1 << width) - 1
// 2. mask2 = 1 << (width - 1)
// 3. amount = datasize - width
// 4. 0 < width < datasize
if (m_value->child(0)->opcode() == BitXor
&& m_value->child(0)->child(0)->opcode() == BitAnd
&& m_value->child(0)->child(0)->child(1)->hasInt()
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(1)->hasInt()) {
uint64_t mask1 = m_value->child(0)->child(0)->child(1)->asInt();
uint64_t mask2 = m_value->child(0)->child(1)->asInt();
uint64_t mask3 = m_value->child(1)->asInt();
uint64_t width = WTF::bitCount(mask1);
uint64_t datasize = m_value->child(0)->child(0)->type() == Int64 ? 64 : 32;
bool isValidMask1 = mask1 && !(mask1 & (mask1 + 1)) && width < datasize;
bool isValidMask2 = mask2 == mask3 && ((mask2 << 1) - 1) == mask1;
if (isValidMask1 && isValidMask2) {
Value* amount = m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), datasize - width);
Value* shlValue = m_insertionSet.insert<Value>(m_index, Shl, m_value->origin(), m_value->child(0)->child(0)->child(0), amount);
replaceWithNew<Value>(SShr, m_value->origin(), shlValue, amount);
break;
}
}
// Turn this: Sub(constant1, constant2)
// Into this: constant1 - constant2
if (Value* constantSub = m_value->child(0)->subConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constantSub);
break;
}
if (m_value->isInteger()) {
// Turn this: Sub(Neg(value), 1)
// Into this: BitXor(value, -1)
if (m_value->child(0)->opcode() == Neg && m_value->child(1)->isInt(1)) {
Value* minusOne;
if (m_value->child(0)->child(0)->type() == Int32)
minusOne = m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), -1);
else
minusOne = m_insertionSet.insert<Const64Value>(m_index, m_value->origin(), -1);
replaceWithNew<Value>(BitXor, m_value->origin(), m_value->child(0)->child(0), minusOne);
break;
}
// Turn this: Sub(value, constant)
// Into this: Add(value, -constant)
if (Value* negatedConstant = m_value->child(1)->negConstant(m_proc)) {
m_insertionSet.insertValue(m_index, negatedConstant);
replaceWithNew<Value>(
Add, m_value->origin(), m_value->child(0), negatedConstant);
break;
}
// Turn this: Sub(0, value)
// Into this: Neg(value)
if (m_value->child(0)->isInt(0)) {
replaceWithNew<Value>(Neg, m_value->origin(), m_value->child(1));
break;
}
// Turn this: Sub(value, value)
// Into this: 0
if (m_value->child(0) == m_value->child(1)) {
replaceWithNewValue(m_proc.addIntConstant(m_value, 0));
break;
}
// Turn this: Sub(value, Neg(otherValue))
// Into this: Add(value, otherValue)
if (m_value->child(1)->opcode() == Neg) {
replaceWithNew<Value>(Add, m_value->origin(), m_value->child(0), m_value->child(1)->child(0));
break;
}
// Turn this: Sub(Neg(value), value2)
// Into this: Neg(Add(value, value2))
if (m_value->child(0)->opcode() == Neg) {
replaceWithNew<Value>(Neg, m_value->origin(),
m_insertionSet.insert<Value>(m_index, Add, m_value->origin(), m_value->child(0)->child(0), m_value->child(1)));
break;
}
// Turn this: Sub(Sub(a, b), c)
// Into this: Sub(a, Add(b, c))
if (m_value->child(0)->opcode() == Sub) {
replaceWithNew<Value>(Sub, m_value->origin(), m_value->child(0)->child(0),
m_insertionSet.insert<Value>(m_index, Add, m_value->origin(), m_value->child(0)->child(1), m_value->child(1)));
break;
}
// Turn this: Sub(a, Sub(b, c))
// Into this: Add(Sub(a, b), c)
if (m_value->child(1)->opcode() == Sub) {
replaceWithNew<Value>(Add, m_value->origin(),
m_insertionSet.insert<Value>(m_index, Sub, m_value->origin(), m_value->child(0), m_value->child(1)->child(0)),
m_value->child(1)->child(1));
break;
}
// Turn this: Sub(Add(a, b), c)
// Into this: Add(a, Sub(b, c))
if (m_value->child(0)->opcode() == Add) {
replaceWithNew<Value>(Add, m_value->origin(), m_value->child(0)->child(0),
m_insertionSet.insert<Value>(m_index, Sub, m_value->origin(), m_value->child(0)->child(1), m_value->child(1)));
break;
}
if (handleMulDistributivity())
break;
}
break;
case Neg:
// Turn this: Neg(constant)
// Into this: -constant
if (Value* constant = m_value->child(0)->negConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
// Turn this: Neg(Neg(value))
// Into this: value
if (m_value->child(0)->opcode() == Neg) {
replaceWithIdentity(m_value->child(0)->child(0));
break;
}
if (m_value->isInteger()) {
// Turn this: Integer Neg(Sub(value, otherValue))
// Into this: Sub(otherValue, value)
if (m_value->child(0)->opcode() == Sub) {
replaceWithNew<Value>(Sub, m_value->origin(), m_value->child(0)->child(1), m_value->child(0)->child(0));
break;
}
// Turn this: Integer Neg(Mul(value, c))
// Into this: Mul(value, -c), as long as -c does not overflow
if (m_value->child(0)->opcode() == Mul && m_value->child(0)->child(1)->hasInt()) {
int64_t factor = m_value->child(0)->child(1)->asInt();
if (m_value->type() == Int32 && factor != std::numeric_limits<int32_t>::min()) {
Value* newFactor = m_insertionSet.insert<Const32Value>(m_index, m_value->child(0)->child(1)->origin(), -factor);
replaceWithNew<Value>(Mul, m_value->origin(), m_value->child(0)->child(0), newFactor);
} else if (m_value->type() == Int64 && factor != std::numeric_limits<int64_t>::min()) {
Value* newFactor = m_insertionSet.insert<Const64Value>(m_index, m_value->child(0)->child(1)->origin(), -factor);
replaceWithNew<Value>(Mul, m_value->origin(), m_value->child(0)->child(0), newFactor);
}
}
}
break;
case Mul:
handleCommutativity();
// Turn this: Mul(constant1, constant2)
// Into this: constant1 * constant2
if (Value* value = m_value->child(0)->mulConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(value);
break;
}
if (m_value->child(1)->hasInt()) {
int64_t factor = m_value->child(1)->asInt();
// Turn this: Mul(value, 0)
// Into this: 0
// Note that we don't do this for doubles because that's wrong. For example, -1 * 0
// and 1 * 0 yield different results.
if (!factor) {
replaceWithIdentity(m_value->child(1));
break;
}
// Turn this: Mul(value, 1)
// Into this: value
if (factor == 1) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: Mul(value, -1)
// Into this: Neg(value)
if (factor == -1) {
replaceWithNew<Value>(Neg, m_value->origin(), m_value->child(0));
break;
}
// Turn this: Mul(value, constant)
// Into this: Shl(value, log2(constant))
if (hasOneBitSet(factor)) {
unsigned shiftAmount = WTF::fastLog2(static_cast<uint64_t>(factor));
replaceWithNewValue(
m_proc.add<Value>(
Shl, m_value->origin(), m_value->child(0),
m_insertionSet.insert<Const32Value>(
m_index, m_value->origin(), shiftAmount)));
break;
}
} else if (m_value->child(1)->hasDouble()) {
double factor = m_value->child(1)->asDouble();
// Turn this: Mul(value, 1)
// Into this: value
if (factor == 1) {
replaceWithIdentity(m_value->child(0));
break;
}
}
if (m_value->isInteger()) {
// Turn this: Integer Mul(value, Neg(otherValue))
// Into this: Neg(Mul(value, otherValue))
if (m_value->child(1)->opcode() == Neg) {
Value* newMul = m_insertionSet.insert<Value>(m_index, Mul, m_value->origin(), m_value->child(0), m_value->child(1)->child(0));
replaceWithNew<Value>(Neg, m_value->origin(), newMul);
break;
}
// Turn this: Integer Mul(Neg(value), otherValue)
// Into this: Neg(Mul(value, value2))
if (m_value->child(0)->opcode() == Neg) {
Value* newMul = m_insertionSet.insert<Value>(m_index, Mul, m_value->origin(), m_value->child(0)->child(0), m_value->child(1));
replaceWithNew<Value>(Neg, m_value->origin(), newMul);
break;
}
}
break;
case Div:
// Turn this: Div(constant1, constant2)
// Into this: constant1 / constant2
// Note that this uses Div<Chill> semantics. That's fine, because the rules for Div
// are strictly weaker: it has corner cases where it's allowed to do anything it
// likes.
if (replaceWithNewValue(m_value->child(0)->divConstant(m_proc, m_value->child(1))))
break;
if (m_value->child(1)->hasInt()) {
switch (m_value->child(1)->asInt()) {
case -1:
// Turn this: Div(value, -1)
// Into this: Neg(value)
replaceWithNewValue(
m_proc.add<Value>(Neg, m_value->origin(), m_value->child(0)));
break;
case 0:
// Turn this: Div(value, 0)
// Into this: 0
// We can do this because it's precisely correct for ChillDiv and for Div we
// are allowed to do whatever we want.
replaceWithIdentity(m_value->child(1));
break;
case 1:
// Turn this: Div(value, 1)
// Into this: value
replaceWithIdentity(m_value->child(0));
break;
default:
// Perform super comprehensive strength reduction of division. Currently we
// only do this for 32-bit divisions, since we need a high multiply
// operation. We emulate it using 64-bit multiply. We can't emulate 64-bit
// high multiply with a 128-bit multiply because we don't have a 128-bit
// multiply. We could do it with a patchpoint if we cared badly enough.
if (m_value->type() != Int32)
break;
if (m_proc.optLevel() < 2)
break;
int32_t divisor = m_value->child(1)->asInt32();
DivisionMagic<int32_t> magic = computeDivisionMagic(divisor);
// Perform the "high" multiplication. We do it just to get the high bits.
// This is sort of like multiplying by the reciprocal, just more gnarly. It's
// from Hacker's Delight and I don't claim to understand it.
Value* magicQuotient = m_insertionSet.insert<Value>(
m_index, Trunc, m_value->origin(),
m_insertionSet.insert<Value>(
m_index, ZShr, m_value->origin(),
m_insertionSet.insert<Value>(
m_index, Mul, m_value->origin(),
m_insertionSet.insert<Value>(
m_index, SExt32, m_value->origin(), m_value->child(0)),
m_insertionSet.insert<Const64Value>(
m_index, m_value->origin(), magic.magicMultiplier)),
m_insertionSet.insert<Const32Value>(
m_index, m_value->origin(), 32)));
if (divisor > 0 && magic.magicMultiplier < 0) {
magicQuotient = m_insertionSet.insert<Value>(
m_index, Add, m_value->origin(), magicQuotient, m_value->child(0));
}
if (divisor < 0 && magic.magicMultiplier > 0) {
magicQuotient = m_insertionSet.insert<Value>(
m_index, Sub, m_value->origin(), magicQuotient, m_value->child(0));
}
if (magic.shift > 0) {
magicQuotient = m_insertionSet.insert<Value>(
m_index, SShr, m_value->origin(), magicQuotient,
m_insertionSet.insert<Const32Value>(
m_index, m_value->origin(), magic.shift));
}
replaceWithIdentity(
m_insertionSet.insert<Value>(
m_index, Add, m_value->origin(), magicQuotient,
m_insertionSet.insert<Value>(
m_index, ZShr, m_value->origin(), magicQuotient,
m_insertionSet.insert<Const32Value>(
m_index, m_value->origin(), 31))));
break;
}
break;
}
break;
case UDiv:
// Turn this: UDiv(constant1, constant2)
// Into this: constant1 / constant2
if (replaceWithNewValue(m_value->child(0)->uDivConstant(m_proc, m_value->child(1))))
break;
if (m_value->child(1)->hasInt()) {
switch (m_value->child(1)->asInt()) {
case 0:
// Turn this: UDiv(value, 0)
// Into this: 0
// We can do whatever we want here so we might as well do the chill thing,
// in case we add chill versions of UDiv in the future.
replaceWithIdentity(m_value->child(1));
break;
case 1:
// Turn this: UDiv(value, 1)
// Into this: value
replaceWithIdentity(m_value->child(0));
break;
default:
// FIXME: We should do comprehensive strength reduction for unsigned numbers. Likely,
// we will just want copy what llvm does. https://bugs.webkit.org/show_bug.cgi?id=164809
break;
}
}
break;
case Mod:
// Turn this: Mod(constant1, constant2)
// Into this: constant1 % constant2
// Note that this uses Mod<Chill> semantics.
if (replaceWithNewValue(m_value->child(0)->modConstant(m_proc, m_value->child(1))))
break;
// Modulo by constant is more efficient if we turn it into Div, and then let Div get
// optimized.
if (m_value->child(1)->hasInt()) {
switch (m_value->child(1)->asInt()) {
case 0:
// Turn this: Mod(value, 0)
// Into this: 0
// This is correct according to ChillMod semantics.
replaceWithIdentity(m_value->child(1));
break;
default:
if (m_proc.optLevel() < 2)
break;
// Turn this: Mod(N, D)
// Into this: Sub(N, Mul(Div(N, D), D))
//
// This is a speed-up because we use our existing Div optimizations.
//
// Here's an easier way to look at it:
// N % D = N - N / D * D
//
// Note that this does not work for D = 0 and ChillMod. The expected result is 0.
// That's why we have a special-case above.
// X % 0 = X - X / 0 * 0 = X (should be 0)
//
// This does work for the D = -1 special case.
// -2^31 % -1 = -2^31 - -2^31 / -1 * -1
// = -2^31 - -2^31 * -1
// = -2^31 - -2^31
// = 0
Kind divKind = Div;
divKind.setIsChill(m_value->isChill());
replaceWithIdentity(
m_insertionSet.insert<Value>(
m_index, Sub, m_value->origin(),
m_value->child(0),
m_insertionSet.insert<Value>(
m_index, Mul, m_value->origin(),
m_insertionSet.insert<Value>(
m_index, divKind, m_value->origin(),
m_value->child(0), m_value->child(1)),
m_value->child(1))));
break;
}
break;
}
break;
case UMod:
// Turn this: UMod(constant1, constant2)
// Into this: constant1 % constant2
replaceWithNewValue(m_value->child(0)->uModConstant(m_proc, m_value->child(1)));
// FIXME: We should do what we do for Mod since the same principle applies here.
// https://bugs.webkit.org/show_bug.cgi?id=164809
break;
case FMax:
replaceWithNewValue(m_value->child(0)->fMaxConstant(m_proc, m_value->child(1)));
break;
case FMin:
replaceWithNewValue(m_value->child(0)->fMinConstant(m_proc, m_value->child(1)));
break;
case BitAnd:
handleCommutativity();
// Turn this: BitAnd(constant1, constant2)
// Into this: constant1 & constant2
if (Value* constantBitAnd = m_value->child(0)->bitAndConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constantBitAnd);
break;
}
// Turn this: BitAnd(BitAnd(value, constant1), constant2)
// Into this: BitAnd(value, constant1 & constant2).
if (m_value->child(0)->opcode() == BitAnd) {
Value* newConstant = m_value->child(1)->bitAndConstant(m_proc, m_value->child(0)->child(1));
if (newConstant) {
m_insertionSet.insertValue(m_index, newConstant);
m_value->child(0) = m_value->child(0)->child(0);
m_value->child(1) = newConstant;
m_changed = true;
}
}
// Turn this: BitAnd(valueX, valueX)
// Into this: valueX.
if (m_value->child(0) == m_value->child(1)) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: BitAnd(value, zero-constant)
// Into this: zero-constant.
if (m_value->child(1)->isInt(0)) {
replaceWithIdentity(m_value->child(1));
break;
}
// Turn this: BitAnd(ZShr(value, shiftAmount), mask)
// Conditions:
// 1. mask = (1 << width) - 1
// 2. 0 <= shiftAmount < datasize
// 3. 0 < width < datasize
// 4. shiftAmount + width >= datasize
// Into this: ZShr(value, shiftAmount)
if (m_value->child(0)->opcode() == ZShr
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(0)->child(1)->asInt() >= 0
&& m_value->child(1)->hasInt()) {
uint64_t shiftAmount = m_value->child(0)->child(1)->asInt();
uint64_t mask = m_value->child(1)->asInt();
bool isValidMask = mask && !(mask & (mask + 1));
uint64_t datasize = m_value->child(0)->child(0)->type() == Int64 ? 64 : 32;
uint64_t width = WTF::bitCount(mask);
if (shiftAmount < datasize && isValidMask && shiftAmount + width >= datasize) {
replaceWithIdentity(m_value->child(0));
break;
}
}
// Turn this: BitAnd(Shl(value, shiftAmount), maskShift)
// Into this: Shl(BitAnd(value, mask), shiftAmount)
// Conditions:
// 1. maskShift = mask << shiftAmount
// 2. mask = (1 << width) - 1
// 3. 0 <= shiftAmount < datasize
// 4. 0 < width < datasize
// 5. shiftAmount + width <= datasize
if (m_value->child(0)->opcode() == Shl
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(0)->child(1)->asInt() >= 0
&& m_value->child(1)->hasInt()) {
uint64_t shiftAmount = m_value->child(0)->child(1)->asInt();
uint64_t maskShift = m_value->child(1)->asInt();
uint64_t maskShiftAmount = WTF::countTrailingZeros(maskShift);
uint64_t mask = maskShift >> maskShiftAmount;
uint64_t width = WTF::bitCount(mask);
uint64_t datasize = m_value->child(0)->child(0)->type() == Int64 ? 64 : 32;
bool isValidShiftAmount = shiftAmount == maskShiftAmount && shiftAmount < datasize;
bool isValidMask = mask && !(mask & (mask + 1)) && width < datasize;
if (isValidShiftAmount && isValidMask && shiftAmount + width <= datasize) {
Value* maskValue;
if (datasize == 32)
maskValue = m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), mask);
else
maskValue = m_insertionSet.insert<Const64Value>(m_index, m_value->origin(), mask);
Value* bitAnd = m_insertionSet.insert<Value>(m_index, BitAnd, m_value->origin(), m_value->child(0)->child(0), maskValue);
replaceWithNew<Value>(Shl, m_value->origin(), bitAnd, m_value->child(0)->child(1));
break;
}
}
// Turn this: BitAnd(value, all-ones)
// Into this: value.
if ((m_value->type() == Int64 && m_value->child(1)->isInt64(std::numeric_limits<uint64_t>::max()))
|| (m_value->type() == Int32 && m_value->child(1)->isInt32(std::numeric_limits<uint32_t>::max()))) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: BitAnd(64-bit value, 32 ones)
// Into this: ZExt32(Trunc(64-bit value))
if (m_value->child(1)->isInt64(0xffffffffllu)) {
Value* newValue = m_insertionSet.insert<Value>(
m_index, ZExt32, m_value->origin(),
m_insertionSet.insert<Value>(m_index, Trunc, m_value->origin(), m_value->child(0)));
replaceWithIdentity(newValue);
break;
}
// Turn this: BitAnd(SExt8(value), mask) where (mask & 0xffffff00) == 0
// Into this: BitAnd(value, mask)
if (m_value->child(0)->opcode() == SExt8 && m_value->child(1)->hasInt32()
&& !(m_value->child(1)->asInt32() & 0xffffff00)) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
break;
}
// Turn this: BitAnd(SExt16(value), mask) where (mask & 0xffff0000) == 0
// Into this: BitAnd(value, mask)
if (m_value->child(0)->opcode() == SExt16 && m_value->child(1)->hasInt32()
&& !(m_value->child(1)->asInt32() & 0xffff0000)) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
break;
}
// Turn this: BitAnd(SExt32(value), mask) where (mask & 0xffffffff00000000) == 0
// Into this: BitAnd(ZExt32(value), mask)
if (m_value->child(0)->opcode() == SExt32 && m_value->child(1)->hasInt32()
&& !(m_value->child(1)->asInt32() & 0xffffffff00000000llu)) {
m_value->child(0) = m_insertionSet.insert<Value>(
m_index, ZExt32, m_value->origin(),
m_value->child(0)->child(0), m_value->child(0)->child(1));
m_changed = true;
break;
}
// Turn this: BitAnd(Op(value, constant1), constant2)
// where !(constant1 & constant2)
// and Op is BitOr or BitXor
// into this: BitAnd(value, constant2)
if (m_value->child(1)->hasInt()) {
bool replaced = false;
int64_t constant2 = m_value->child(1)->asInt();
switch (m_value->child(0)->opcode()) {
case BitOr:
case BitXor:
if (m_value->child(0)->child(1)->hasInt()
&& !(m_value->child(0)->child(1)->asInt() & constant2)) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
replaced = true;
break;
}
break;
default:
break;
}
if (replaced)
break;
}
// Turn this: BitAnd(BitXor(x1, allOnes), BitXor(x2, allOnes)
// Into this: BitXor(BitOr(x1, x2), allOnes)
// By applying De Morgan laws
if (m_value->child(0)->opcode() == BitXor
&& m_value->child(1)->opcode() == BitXor
&& ((m_value->type() == Int64
&& m_value->child(0)->child(1)->isInt64(std::numeric_limits<uint64_t>::max())
&& m_value->child(1)->child(1)->isInt64(std::numeric_limits<uint64_t>::max()))
|| (m_value->type() == Int32
&& m_value->child(0)->child(1)->isInt32(std::numeric_limits<uint32_t>::max())
&& m_value->child(1)->child(1)->isInt32(std::numeric_limits<uint32_t>::max())))) {
Value* bitOr = m_insertionSet.insert<Value>(m_index, BitOr, m_value->origin(), m_value->child(0)->child(0), m_value->child(1)->child(0));
replaceWithNew<Value>(BitXor, m_value->origin(), bitOr, m_value->child(1)->child(1));
break;
}
// Turn this: BitAnd(BitXor(x, allOnes), c)
// Into this: BitXor(BitOr(x, ~c), allOnes)
// This is a variation on the previous optimization, treating c as if it were BitXor(~c, allOnes)
// It does not reduce the number of operations, but provides some normalization (we try to get BitXor by allOnes at the outermost point), and some chance to float Xors to a place where they might get eliminated.
if (m_value->child(0)->opcode() == BitXor
&& m_value->child(1)->hasInt()
&& ((m_value->type() == Int64
&& m_value->child(0)->child(1)->isInt64(std::numeric_limits<uint64_t>::max()))
|| (m_value->type() == Int32
&& m_value->child(0)->child(1)->isInt32(std::numeric_limits<uint32_t>::max())))) {
Value* newConstant = m_value->child(1)->bitXorConstant(m_proc, m_value->child(0)->child(1));
ASSERT(newConstant);
m_insertionSet.insertValue(m_index, newConstant);
Value* bitOr = m_insertionSet.insert<Value>(m_index, BitOr, m_value->origin(), m_value->child(0)->child(0), newConstant);
replaceWithNew<Value>(BitXor, m_value->origin(), bitOr, m_value->child(0)->child(1));
break;
}
break;
case BitOr:
handleCommutativity();
// Turn this: BitOr(constant1, constant2)
// Into this: constant1 | constant2
if (Value* constantBitOr = m_value->child(0)->bitOrConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constantBitOr);
break;
}
// Turn this: BitOr(BitOr(value, constant1), constant2)
// Into this: BitOr(value, constant1 & constant2).
if (m_value->child(0)->opcode() == BitOr) {
Value* newConstant = m_value->child(1)->bitOrConstant(m_proc, m_value->child(0)->child(1));
if (newConstant) {
m_insertionSet.insertValue(m_index, newConstant);
m_value->child(0) = m_value->child(0)->child(0);
m_value->child(1) = newConstant;
m_changed = true;
}
}
// Turn this: BitOr(valueX, valueX)
// Into this: valueX.
if (m_value->child(0) == m_value->child(1)) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: BitOr(value, zero-constant)
// Into this: value.
if (m_value->child(1)->isInt(0)) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: BitOr(value, all-ones)
// Into this: all-ones.
if ((m_value->type() == Int64 && m_value->child(1)->isInt64(std::numeric_limits<uint64_t>::max()))
|| (m_value->type() == Int32 && m_value->child(1)->isInt32(std::numeric_limits<uint32_t>::max()))) {
replaceWithIdentity(m_value->child(1));
break;
}
// Turn this: BitOr(BitXor(x1, allOnes), BitXor(x2, allOnes)
// Into this: BitXor(BitAnd(x1, x2), allOnes)
// By applying De Morgan laws
if (m_value->child(0)->opcode() == BitXor
&& m_value->child(1)->opcode() == BitXor
&& ((m_value->type() == Int64
&& m_value->child(0)->child(1)->isInt64(std::numeric_limits<uint64_t>::max())
&& m_value->child(1)->child(1)->isInt64(std::numeric_limits<uint64_t>::max()))
|| (m_value->type() == Int32
&& m_value->child(0)->child(1)->isInt32(std::numeric_limits<uint32_t>::max())
&& m_value->child(1)->child(1)->isInt32(std::numeric_limits<uint32_t>::max())))) {
Value* bitAnd = m_insertionSet.insert<Value>(m_index, BitAnd, m_value->origin(), m_value->child(0)->child(0), m_value->child(1)->child(0));
replaceWithNew<Value>(BitXor, m_value->origin(), bitAnd, m_value->child(1)->child(1));
break;
}
// Turn this: BitOr(BitXor(x, allOnes), c)
// Into this: BitXor(BitAnd(x, ~c), allOnes)
// This is a variation on the previous optimization, treating c as if it were BitXor(~c, allOnes)
// It does not reduce the number of operations, but provides some normalization (we try to get BitXor by allOnes at the outermost point), and some chance to float Xors to a place where they might get eliminated.
if (m_value->child(0)->opcode() == BitXor
&& m_value->child(1)->hasInt()
&& ((m_value->type() == Int64
&& m_value->child(0)->child(1)->isInt64(std::numeric_limits<uint64_t>::max()))
|| (m_value->type() == Int32
&& m_value->child(0)->child(1)->isInt32(std::numeric_limits<uint32_t>::max())))) {
Value* newConstant = m_value->child(1)->bitXorConstant(m_proc, m_value->child(0)->child(1));
ASSERT(newConstant);
m_insertionSet.insertValue(m_index, newConstant);
Value* bitAnd = m_insertionSet.insert<Value>(m_index, BitAnd, m_value->origin(), m_value->child(0)->child(0), newConstant);
replaceWithNew<Value>(BitXor, m_value->origin(), bitAnd, m_value->child(0)->child(1));
break;
}
if (handleBitAndDistributivity())
break;
break;
case BitXor:
handleCommutativity();
// Turn this: BitXor(constant1, constant2)
// Into this: constant1 ^ constant2
if (Value* constantBitXor = m_value->child(0)->bitXorConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constantBitXor);
break;
}
// Turn this: BitXor(BitXor(value, constant1), constant2)
// Into this: BitXor(value, constant1 ^ constant2).
if (m_value->child(0)->opcode() == BitXor) {
Value* newConstant = m_value->child(1)->bitXorConstant(m_proc, m_value->child(0)->child(1));
if (newConstant) {
m_insertionSet.insertValue(m_index, newConstant);
m_value->child(0) = m_value->child(0)->child(0);
m_value->child(1) = newConstant;
m_changed = true;
}
}
// Turn this: BitXor(compare, 1)
// Into this: invertedCompare
if (m_value->child(1)->isInt32(1)) {
if (Value* invertedCompare = m_value->child(0)->invertedCompare(m_proc)) {
replaceWithNewValue(invertedCompare);
break;
}
}
// Turn this: BitXor(valueX, valueX)
// Into this: zero-constant.
if (m_value->child(0) == m_value->child(1)) {
replaceWithNewValue(m_proc.addIntConstant(m_value, 0));
break;
}
// Turn this: BitXor(value, zero-constant)
// Into this: value.
if (m_value->child(1)->isInt(0)) {
replaceWithIdentity(m_value->child(0));
break;
}
if (handleBitAndDistributivity())
break;
break;
case Shl:
// Turn this: Shl(constant1, constant2)
// Into this: constant1 << constant2
if (Value* constant = m_value->child(0)->shlConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constant);
break;
}
// Turn this: Shl(<S|Z>Shr(@x, @const), @const)
// Into this: BitAnd(@x, -(1<<@const))
if ((m_value->child(0)->opcode() == SShr || m_value->child(0)->opcode() == ZShr)
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(1)->hasInt()
&& m_value->child(0)->child(1)->asInt() == m_value->child(1)->asInt()) {
int shiftAmount = m_value->child(1)->asInt() & (m_value->type() == Int32 ? 31 : 63);
Value* newConst = m_proc.addIntConstant(m_value, - static_cast<int64_t>(1ull << shiftAmount));
m_insertionSet.insertValue(m_index, newConst);
replaceWithNew<Value>(BitAnd, m_value->origin(), m_value->child(0)->child(0), newConst);
break;
}
handleShiftAmount();
break;
case SShr:
// Turn this: SShr(constant1, constant2)
// Into this: constant1 >> constant2
if (Value* constant = m_value->child(0)->sShrConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constant);
break;
}
if (m_value->child(1)->hasInt32()
&& m_value->child(0)->opcode() == Shl
&& m_value->child(0)->child(1)->hasInt32()
&& m_value->child(1)->asInt32() == m_value->child(0)->child(1)->asInt32()) {
switch (m_value->child(1)->asInt32()) {
case 16:
if (m_value->type() == Int32) {
// Turn this: SShr(Shl(value, 16), 16)
// Into this: SExt16(value)
replaceWithNewValue(
m_proc.add<Value>(
SExt16, m_value->origin(), m_value->child(0)->child(0)));
}
break;
case 24:
if (m_value->type() == Int32) {
// Turn this: SShr(Shl(value, 24), 24)
// Into this: SExt8(value)
replaceWithNewValue(
m_proc.add<Value>(
SExt8, m_value->origin(), m_value->child(0)->child(0)));
}
break;
case 32:
if (m_value->type() == Int64) {
// Turn this: SShr(Shl(value, 32), 32)
// Into this: SExt32(Trunc(value))
replaceWithNewValue(
m_proc.add<Value>(
SExt32, m_value->origin(),
m_insertionSet.insert<Value>(
m_index, Trunc, m_value->origin(),
m_value->child(0)->child(0))));
}
break;
// FIXME: Add cases for 48 and 56, but that would translate to SExt32(SExt8) or
// SExt32(SExt16), which we don't currently lower efficiently.
default:
break;
}
if (m_value->opcode() != SShr)
break;
}
handleShiftAmount();
break;
case ZShr:
// Turn this: ZShr(constant1, constant2)
// Into this: (unsigned)constant1 >> constant2
if (Value* constant = m_value->child(0)->zShrConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constant);
break;
}
// Turn this: ZShr(Shl(value, amount)), amount)
// Into this: BitAnd(value, mask)
// Conditions:
// 1. 0 <= amount < datasize
// 2. width = datasize - amount
// 3. mask is !(mask & (mask + 1)) where bitCount(mask) == width
if (m_value->child(0)->opcode() == Shl
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(0)->child(1)->asInt() >= 0
&& m_value->child(1)->hasInt()
&& m_value->child(1)->asInt() >= 0) {
uint64_t amount1 = m_value->child(0)->child(1)->asInt();
uint64_t amount2 = m_value->child(1)->asInt();
uint64_t datasize = m_value->child(0)->child(0)->type() == Int64 ? 64 : 32;
if (amount1 == amount2 && amount1 < datasize) {
uint64_t width = datasize - amount1;
uint64_t mask = (1ULL << width) - 1ULL;
Value* maskValue;
if (datasize == 32)
maskValue = m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), mask);
else
maskValue = m_insertionSet.insert<Const64Value>(m_index, m_value->origin(), mask);
replaceWithNew<Value>(BitAnd, m_value->origin(), m_value->child(0)->child(0), maskValue);
break;
}
}
// Turn this: ZShr(BitAnd(value, maskShift), shiftAmount)
// Into this: BitAnd(ZShr(value, shiftAmount), mask)
// Conditions:
// 1. maskShift = mask << shiftAmount
// 2. mask = (1 << width) - 1
// 3. 0 <= shiftAmount < datasize
// 4. 0 < width < datasize
// 5. shiftAmount + width <= datasize
if (m_value->child(0)->opcode() == BitAnd
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(1)->hasInt()
&& m_value->child(1)->asInt() >= 0) {
uint64_t shiftAmount = m_value->child(1)->asInt();
uint64_t maskShift = m_value->child(0)->child(1)->asInt();
uint64_t maskShiftAmount = WTF::countTrailingZeros(maskShift);
uint64_t mask = maskShift >> maskShiftAmount;
uint64_t width = WTF::bitCount(mask);
uint64_t datasize = m_value->child(0)->child(0)->type() == Int64 ? 64 : 32;
bool isValidShiftAmount = maskShiftAmount == shiftAmount && shiftAmount < datasize;
bool isValidMask = mask && !(mask & (mask + 1)) && width < datasize;
if (isValidShiftAmount && isValidMask && shiftAmount + width <= datasize) {
Value* maskValue;
if (datasize == 32)
maskValue = m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), mask);
else
maskValue = m_insertionSet.insert<Const64Value>(m_index, m_value->origin(), mask);
Value* shiftValue = m_insertionSet.insert<Value>(m_index, ZShr, m_value->origin(), m_value->child(0)->child(0), m_value->child(1));
replaceWithNew<Value>(BitAnd, m_value->origin(), shiftValue, maskValue);
break;
}
}
handleShiftAmount();
break;
case RotR:
// Turn this: RotR(constant1, constant2)
// Into this: (constant1 >> constant2) | (constant1 << sizeof(constant1) * 8 - constant2)
if (Value* constant = m_value->child(0)->rotRConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constant);
break;
}
handleShiftAmount();
break;
case RotL:
// Turn this: RotL(constant1, constant2)
// Into this: (constant1 << constant2) | (constant1 >> sizeof(constant1) * 8 - constant2)
if (Value* constant = m_value->child(0)->rotLConstant(m_proc, m_value->child(1))) {
replaceWithNewValue(constant);
break;
}
handleShiftAmount();
break;
case Abs:
// Turn this: Abs(constant)
// Into this: fabs<value->type()>(constant)
if (Value* constant = m_value->child(0)->absConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
// Turn this: Abs(Abs(value))
// Into this: Abs(value)
if (m_value->child(0)->opcode() == Abs) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: Abs(Neg(value))
// Into this: Abs(value)
if (m_value->child(0)->opcode() == Neg) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
break;
}
// Turn this: Abs(BitwiseCast(value))
// Into this: BitwiseCast(And(value, mask-top-bit))
if (m_value->child(0)->opcode() == BitwiseCast) {
Value* mask;
if (m_value->type() == Double)
mask = m_insertionSet.insert<Const64Value>(m_index, m_value->origin(), ~(1ll << 63));
else
mask = m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), ~(1l << 31));
Value* bitAnd = m_insertionSet.insert<Value>(m_index, BitAnd, m_value->origin(),
m_value->child(0)->child(0),
mask);
Value* cast = m_insertionSet.insert<Value>(m_index, BitwiseCast, m_value->origin(), bitAnd);
replaceWithIdentity(cast);
break;
}
break;
case Ceil:
// Turn this: Ceil(constant)
// Into this: ceil<value->type()>(constant)
if (Value* constant = m_value->child(0)->ceilConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
// Turn this: Ceil(roundedValue)
// Into this: roundedValue
if (m_value->child(0)->isRounded()) {
replaceWithIdentity(m_value->child(0));
break;
}
break;
case Floor:
// Turn this: Floor(constant)
// Into this: floor<value->type()>(constant)
if (Value* constant = m_value->child(0)->floorConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
// Turn this: Floor(roundedValue)
// Into this: roundedValue
if (m_value->child(0)->isRounded()) {
replaceWithIdentity(m_value->child(0));
break;
}
break;
case Sqrt:
// Turn this: Sqrt(constant)
// Into this: sqrt<value->type()>(constant)
if (Value* constant = m_value->child(0)->sqrtConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
break;
case BitwiseCast:
// Turn this: BitwiseCast(constant)
// Into this: bitwise_cast<value->type()>(constant)
if (Value* constant = m_value->child(0)->bitwiseCastConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
// Turn this: BitwiseCast(BitwiseCast(value))
// Into this: value
if (m_value->child(0)->opcode() == BitwiseCast) {
replaceWithIdentity(m_value->child(0)->child(0));
break;
}
break;
case SExt8:
// Turn this: SExt8(constant)
// Into this: static_cast<int8_t>(constant)
if (m_value->child(0)->hasInt32()) {
int32_t result = static_cast<int8_t>(m_value->child(0)->asInt32());
replaceWithNewValue(m_proc.addIntConstant(m_value, result));
break;
}
// Turn this: SExt8(SExt8(value))
// or this: SExt8(SExt16(value))
// Into this: SExt8(value)
if (m_value->child(0)->opcode() == SExt8 || m_value->child(0)->opcode() == SExt16) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
}
if (m_value->child(0)->opcode() == BitAnd && m_value->child(0)->child(1)->hasInt32()) {
Value* input = m_value->child(0)->child(0);
int32_t mask = m_value->child(0)->child(1)->asInt32();
// Turn this: SExt8(BitAnd(input, mask)) where (mask & 0xff) == 0xff
// Into this: SExt8(input)
if ((mask & 0xff) == 0xff) {
m_value->child(0) = input;
m_changed = true;
break;
}
// Turn this: SExt8(BitAnd(input, mask)) where (mask & 0x80) == 0
// Into this: BitAnd(input, const & 0x7f)
if (!(mask & 0x80)) {
replaceWithNewValue(
m_proc.add<Value>(
BitAnd, m_value->origin(), input,
m_insertionSet.insert<Const32Value>(
m_index, m_value->origin(), mask & 0x7f)));
break;
}
}
if (!m_proc.hasQuirks()) {
// Turn this: SExt8(AtomicXchg___)
// Into this: AtomicXchg___
if (isAtomicXchg(m_value->child(0)->opcode())
&& m_value->child(0)->as<AtomicValue>()->accessWidth() == Width8) {
replaceWithIdentity(m_value->child(0));
break;
}
}
break;
case SExt16:
// Turn this: SExt16(constant)
// Into this: static_cast<int16_t>(constant)
if (m_value->child(0)->hasInt32()) {
int32_t result = static_cast<int16_t>(m_value->child(0)->asInt32());
replaceWithNewValue(m_proc.addIntConstant(m_value, result));
break;
}
// Turn this: SExt16(SExt16(value))
// Into this: SExt16(value)
if (m_value->child(0)->opcode() == SExt16) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
}
// Turn this: SExt16(SExt8(value))
// Into this: SExt8(value)
if (m_value->child(0)->opcode() == SExt8) {
replaceWithIdentity(m_value->child(0));
break;
}
if (m_value->child(0)->opcode() == BitAnd && m_value->child(0)->child(1)->hasInt32()) {
Value* input = m_value->child(0)->child(0);
int32_t mask = m_value->child(0)->child(1)->asInt32();
// Turn this: SExt16(BitAnd(input, mask)) where (mask & 0xffff) == 0xffff
// Into this: SExt16(input)
if ((mask & 0xffff) == 0xffff) {
m_value->child(0) = input;
m_changed = true;
break;
}
// Turn this: SExt16(BitAnd(input, mask)) where (mask & 0x8000) == 0
// Into this: BitAnd(input, const & 0x7fff)
if (!(mask & 0x8000)) {
replaceWithNewValue(
m_proc.add<Value>(
BitAnd, m_value->origin(), input,
m_insertionSet.insert<Const32Value>(
m_index, m_value->origin(), mask & 0x7fff)));
break;
}
}
if (!m_proc.hasQuirks()) {
// Turn this: SExt16(AtomicXchg___)
// Into this: AtomicXchg___
if (isAtomicXchg(m_value->child(0)->opcode())
&& m_value->child(0)->as<AtomicValue>()->accessWidth() == Width16) {
replaceWithIdentity(m_value->child(0));
break;
}
}
break;
case SExt32:
// Turn this: SExt32(constant)
// Into this: static_cast<int64_t>(constant)
if (m_value->child(0)->hasInt32()) {
replaceWithNewValue(m_proc.addIntConstant(m_value, m_value->child(0)->asInt32()));
break;
}
// Turn this: SExt32(BitAnd(input, mask)) where (mask & 0x80000000) == 0
// Into this: ZExt32(BitAnd(input, mask))
if (m_value->child(0)->opcode() == BitAnd && m_value->child(0)->child(1)->hasInt32()
&& !(m_value->child(0)->child(1)->asInt32() & 0x80000000)) {
replaceWithNewValue(
m_proc.add<Value>(
ZExt32, m_value->origin(), m_value->child(0)));
break;
}
break;
case ZExt32:
// Turn this: ZExt32(constant)
// Into this: static_cast<uint64_t>(static_cast<uint32_t>(constant))
if (m_value->child(0)->hasInt32()) {
replaceWithNewValue(
m_proc.addIntConstant(
m_value,
static_cast<uint64_t>(static_cast<uint32_t>(m_value->child(0)->asInt32()))));
break;
}
break;
case Trunc:
// Turn this: Trunc(constant)
// Into this: static_cast<int32_t>(constant)
if (m_value->child(0)->hasInt64() || m_value->child(0)->hasDouble()) {
replaceWithNewValue(
m_proc.addIntConstant(m_value, static_cast<int32_t>(m_value->child(0)->asInt64())));
break;
}
// Turn this: Trunc(SExt32(value)) or Trunc(ZExt32(value))
// Into this: value
if (m_value->child(0)->opcode() == SExt32 || m_value->child(0)->opcode() == ZExt32) {
replaceWithIdentity(m_value->child(0)->child(0));
break;
}
// Turn this: Trunc(Op(value, constant))
// where !(constant & 0xffffffff)
// and Op is Add, Sub, BitOr, or BitXor
// into this: Trunc(value)
switch (m_value->child(0)->opcode()) {
case Add:
case Sub:
case BitOr:
case BitXor:
if (m_value->child(0)->child(1)->hasInt64()
&& !(m_value->child(0)->child(1)->asInt64() & 0xffffffffll)) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
break;
}
break;
default:
break;
}
break;
case IToD:
// Turn this: IToD(constant)
// Into this: ConstDouble(constant)
if (Value* constant = m_value->child(0)->iToDConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
break;
case IToF:
// Turn this: IToF(constant)
// Into this: ConstFloat(constant)
if (Value* constant = m_value->child(0)->iToFConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
break;
case FloatToDouble:
// We cannot convert some FloatToDouble(DoubleToFloat(value)) to value, because double-to-float will trancate some range of double values into one float.
// Example:
// static_cast<double>(static_cast<float>(1.1)) != 1.1
// Turn this: FloatToDouble(constant)
// Into this: ConstDouble(constant)
if (Value* constant = m_value->child(0)->floatToDoubleConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
break;
case DoubleToFloat:
// Turn this: DoubleToFloat(FloatToDouble(value))
// Into this: value
if (m_value->child(0)->opcode() == FloatToDouble) {
replaceWithIdentity(m_value->child(0)->child(0));
break;
}
// Turn this: DoubleToFloat(constant)
// Into this: ConstFloat(constant)
if (Value* constant = m_value->child(0)->doubleToFloatConstant(m_proc)) {
replaceWithNewValue(constant);
break;
}
break;
case Select:
// Turn this: Select(constant, a, b)
// Into this: constant ? a : b
if (m_value->child(0)->hasInt32()) {
replaceWithIdentity(
m_value->child(0)->asInt32() ? m_value->child(1) : m_value->child(2));
break;
}
// Turn this: Select(Equal(x, 0), a, b)
// Into this: Select(x, b, a)
if (m_value->child(0)->opcode() == Equal && m_value->child(0)->child(1)->isInt(0)) {
m_value->child(0) = m_value->child(0)->child(0);
std::swap(m_value->child(1), m_value->child(2));
m_changed = true;
break;
}
// Turn this: Select(BitXor(bool, 1), a, b)
// Into this: Select(bool, b, a)
if (m_value->child(0)->opcode() == BitXor
&& m_value->child(0)->child(1)->isInt32(1)
&& m_value->child(0)->child(0)->returnsBool()) {
m_value->child(0) = m_value->child(0)->child(0);
std::swap(m_value->child(1), m_value->child(2));
m_changed = true;
break;
}
// Turn this: Select(BitAnd(bool, xyz1), a, b)
// Into this: Select(bool, a, b)
if (m_value->child(0)->opcode() == BitAnd
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(0)->child(1)->asInt() & 1
&& m_value->child(0)->child(0)->returnsBool()) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
break;
}
// Turn this: Select(stuff, x, x)
// Into this: x
if (m_value->child(1) == m_value->child(2)) {
replaceWithIdentity(m_value->child(1));
break;
}
break;
case Load8Z:
case Load8S:
case Load16Z:
case Load16S:
case Load:
case Store8:
case Store16:
case Store: {
Value* address = m_value->lastChild();
MemoryValue* memory = m_value->as<MemoryValue>();
// Turn this: Load(Add(address, offset1), offset = offset2)
// Into this: Load(address, offset = offset1 + offset2)
//
// Also turns this: Store(value, Add(address, offset1), offset = offset2)
// Into this: Store(value, address, offset = offset1 + offset2)
if (address->opcode() == Add && address->child(1)->hasIntPtr()) {
intptr_t offset = address->child(1)->asIntPtr();
if (!sumOverflows<intptr_t>(offset, memory->offset())) {
offset += memory->offset();
Value::OffsetType smallOffset = static_cast<Value::OffsetType>(offset);
if (smallOffset == offset) {
address = address->child(0);
memory->lastChild() = address;
memory->setOffset(smallOffset);
m_changed = true;
}
}
}
// Turn this: Load(constant1, offset = constant2)
// Into this: Load(constant1 + constant2)
//
// This is a fun canonicalization. It purely regresses naively generated code. We rely
// on constant materialization to be smart enough to materialize this constant the smart
// way. We want this canonicalization because we want to know if two memory accesses see
// the same address.
if (memory->offset()) {
if (Value* newAddress = address->addConstant(m_proc, memory->offset())) {
m_insertionSet.insertValue(m_index, newAddress);
address = newAddress;
memory->lastChild() = newAddress;
memory->setOffset(0);
m_changed = true;
}
}
break;
}
case CCall: {
// Turn this: Call(fmod, constant1, constant2)
// Into this: fcall-constant(constant1, constant2)
if (m_value->type() == Double
&& m_value->numChildren() == 3
&& m_value->child(0)->isIntPtr(reinterpret_cast<intptr_t>(tagCFunction<OperationPtrTag>(Math::fmodDouble)))
&& m_value->child(1)->type() == Double
&& m_value->child(2)->type() == Double) {
replaceWithNewValue(m_value->child(1)->modConstant(m_proc, m_value->child(2)));
}
break;
}
case Equal:
handleCommutativity();
// Turn this: Equal(bool, 0)
// Into this: BitXor(bool, 1)
if (m_value->child(0)->returnsBool() && m_value->child(1)->isInt32(0)) {
replaceWithNew<Value>(
BitXor, m_value->origin(), m_value->child(0),
m_insertionSet.insert<Const32Value>(m_index, m_value->origin(), 1));
break;
}
// Turn this Equal(bool, 1)
// Into this: bool
if (m_value->child(0)->returnsBool() && m_value->child(1)->isInt32(1)) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: Equal(const1, const2)
// Into this: const1 == const2
replaceWithNewValue(
m_proc.addBoolConstant(
m_value->origin(),
m_value->child(0)->equalConstant(m_value->child(1))));
break;
case NotEqual:
handleCommutativity();
if (m_value->child(0)->returnsBool()) {
// Turn this: NotEqual(bool, 0)
// Into this: bool
if (m_value->child(1)->isInt32(0)) {
replaceWithIdentity(m_value->child(0));
break;
}
// Turn this: NotEqual(bool, 1)
// Into this: Equal(bool, 0)
if (m_value->child(1)->isInt32(1)) {
replaceWithNew<Value>(
Equal, m_value->origin(), m_value->child(0),
m_insertionSet.insertIntConstant(m_index, m_value->origin(), Int32, 0));
break;
}
}
// Turn this: NotEqual(const1, const2)
// Into this: const1 != const2
replaceWithNewValue(
m_proc.addBoolConstant(
m_value->origin(),
m_value->child(0)->notEqualConstant(m_value->child(1))));
break;
case LessThan:
case GreaterThan:
case LessEqual:
case GreaterEqual:
case Above:
case Below:
case AboveEqual:
case BelowEqual: {
CanonicalizedComparison comparison = canonicalizeComparison(m_value);
TriState result = TriState::Indeterminate;
switch (comparison.opcode) {
case LessThan:
result = comparison.operands[1]->greaterThanConstant(comparison.operands[0]);
break;
case GreaterThan:
result = comparison.operands[1]->lessThanConstant(comparison.operands[0]);
break;
case LessEqual:
result = comparison.operands[1]->greaterEqualConstant(comparison.operands[0]);
break;
case GreaterEqual:
result = comparison.operands[1]->lessEqualConstant(comparison.operands[0]);
break;
case Above:
result = comparison.operands[1]->belowConstant(comparison.operands[0]);
break;
case Below:
result = comparison.operands[1]->aboveConstant(comparison.operands[0]);
break;
case AboveEqual:
result = comparison.operands[1]->belowEqualConstant(comparison.operands[0]);
break;
case BelowEqual:
result = comparison.operands[1]->aboveEqualConstant(comparison.operands[0]);
break;
default:
RELEASE_ASSERT_NOT_REACHED();
break;
}
if (auto* constant = m_proc.addBoolConstant(m_value->origin(), result)) {
replaceWithNewValue(constant);
break;
}
if (comparison.opcode != m_value->opcode()) {
replaceWithNew<Value>(comparison.opcode, m_value->origin(), comparison.operands[0], comparison.operands[1]);
break;
}
break;
}
case EqualOrUnordered:
handleCommutativity();
// Turn this: Equal(const1, const2)
// Into this: isunordered(const1, const2) || const1 == const2.
// Turn this: Equal(value, const_NaN)
// Into this: 1.
replaceWithNewValue(
m_proc.addBoolConstant(
m_value->origin(),
m_value->child(1)->equalOrUnorderedConstant(m_value->child(0))));
break;
case CheckAdd: {
if (replaceWithNewValue(m_value->child(0)->checkAddConstant(m_proc, m_value->child(1))))
break;
handleCommutativity();
if (m_value->child(1)->isInt(0)) {
replaceWithIdentity(m_value->child(0));
break;
}
IntRange leftRange = rangeFor(m_value->child(0));
IntRange rightRange = rangeFor(m_value->child(1));
if (!leftRange.couldOverflowAdd(rightRange, m_value->type())) {
replaceWithNewValue(
m_proc.add<Value>(Add, m_value->origin(), m_value->child(0), m_value->child(1)));
break;
}
break;
}
case CheckSub: {
if (replaceWithNewValue(m_value->child(0)->checkSubConstant(m_proc, m_value->child(1))))
break;
if (m_value->child(1)->isInt(0)) {
replaceWithIdentity(m_value->child(0));
break;
}
if (Value* negatedConstant = m_value->child(1)->checkNegConstant(m_proc)) {
m_insertionSet.insertValue(m_index, negatedConstant);
m_value->as<CheckValue>()->convertToAdd();
m_value->child(1) = negatedConstant;
m_changed = true;
break;
}
IntRange leftRange = rangeFor(m_value->child(0));
IntRange rightRange = rangeFor(m_value->child(1));
if (!leftRange.couldOverflowSub(rightRange, m_value->type())) {
replaceWithNewValue(
m_proc.add<Value>(Sub, m_value->origin(), m_value->child(0), m_value->child(1)));
break;
}
break;
}
case CheckMul: {
if (replaceWithNewValue(m_value->child(0)->checkMulConstant(m_proc, m_value->child(1))))
break;
handleCommutativity();
if (m_value->child(1)->hasInt()) {
bool modified = true;
switch (m_value->child(1)->asInt()) {
case 0:
replaceWithNewValue(m_proc.addIntConstant(m_value, 0));
break;
case 1:
replaceWithIdentity(m_value->child(0));
break;
case 2:
m_value->as<CheckValue>()->convertToAdd();
m_value->child(1) = m_value->child(0);
m_changed = true;
break;
default:
modified = false;
break;
}
if (modified)
break;
}
IntRange leftRange = rangeFor(m_value->child(0));
IntRange rightRange = rangeFor(m_value->child(1));
if (!leftRange.couldOverflowMul(rightRange, m_value->type())) {
replaceWithNewValue(
m_proc.add<Value>(Mul, m_value->origin(), m_value->child(0), m_value->child(1)));
break;
}
break;
}
case Check: {
CheckValue* checkValue = m_value->as<CheckValue>();
if (checkValue->child(0)->isLikeZero()) {
checkValue->replaceWithNop();
m_changed = true;
break;
}
if (checkValue->child(0)->isLikeNonZero()) {
PatchpointValue* patchpoint =
m_insertionSet.insert<PatchpointValue>(m_index, Void, checkValue->origin());
patchpoint->effects = Effects();
patchpoint->effects.reads = HeapRange::top();
patchpoint->effects.exitsSideways = true;
for (unsigned i = 1; i < checkValue->numChildren(); ++i)
patchpoint->append(checkValue->constrainedChild(i));
patchpoint->setGenerator(checkValue->generator());
// Replace the rest of the block with an Oops.
for (unsigned i = m_index + 1; i < m_block->size() - 1; ++i)
m_block->at(i)->replaceWithBottom(m_insertionSet, m_index);
m_block->last()->replaceWithOops(m_block);
m_block->last()->setOrigin(checkValue->origin());
// Replace ourselves last.
checkValue->replaceWithNop();
m_changedCFG = true;
break;
}
if (checkValue->child(0)->opcode() == NotEqual
&& checkValue->child(0)->child(1)->isInt(0)) {
checkValue->child(0) = checkValue->child(0)->child(0);
m_changed = true;
}
if (m_proc.optLevel() < 2)
break;
// If we are checking some bounded-size SSA expression that leads to a Select that
// has a constant as one of its results, then turn the Select into a Branch and split
// the code between the Check and the Branch. For example, this:
//
// @a = Select(@p, @x, 42)
// @b = Add(@a, 35)
// Check(@b)
//
// becomes this:
//
// Branch(@p, #truecase, #falsecase)
//
// BB#truecase:
// @b_truecase = Add(@x, 35)
// Check(@b_truecase)
// Upsilon(@x, ^a)
// Upsilon(@b_truecase, ^b)
// Jump(#continuation)
//
// BB#falsecase:
// @b_falsecase = Add(42, 35)
// Check(@b_falsecase)
// Upsilon(42, ^a)
// Upsilon(@b_falsecase, ^b)
// Jump(#continuation)
//
// BB#continuation:
// @a = Phi()
// @b = Phi()
//
// The goal of this optimization is to kill a lot of code in one of those basic
// blocks. This is pretty much guaranteed since one of those blocks will replace all
// uses of the Select with a constant, and that constant will be transitively used
// from the check.
static constexpr unsigned selectSpecializationBound = 3;
Value* select = findRecentNodeMatching(
m_value->child(0), selectSpecializationBound,
[&] (Value* value) -> bool {
return value->opcode() == Select
&& (value->child(1)->isConstant() && value->child(2)->isConstant());
});
if (select) {
specializeSelect(select);
break;
}
break;
}
case Branch: {
// Turn this: Branch(NotEqual(x, 0))
// Into this: Branch(x)
if (m_value->child(0)->opcode() == NotEqual && m_value->child(0)->child(1)->isInt(0)) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
}
// Turn this: Branch(Equal(x, 0), then, else)
// Into this: Branch(x, else, then)
if (m_value->child(0)->opcode() == Equal && m_value->child(0)->child(1)->isInt(0)) {
m_value->child(0) = m_value->child(0)->child(0);
std::swap(m_block->taken(), m_block->notTaken());
m_changed = true;
}
// Turn this: Branch(BitXor(bool, 1), then, else)
// Into this: Branch(bool, else, then)
if (m_value->child(0)->opcode() == BitXor
&& m_value->child(0)->child(1)->isInt32(1)
&& m_value->child(0)->child(0)->returnsBool()) {
m_value->child(0) = m_value->child(0)->child(0);
std::swap(m_block->taken(), m_block->notTaken());
m_changed = true;
}
// Turn this: Branch(BitAnd(bool, xyb1), then, else)
// Into this: Branch(bool, then, else)
if (m_value->child(0)->opcode() == BitAnd
&& m_value->child(0)->child(1)->hasInt()
&& m_value->child(0)->child(1)->asInt() & 1
&& m_value->child(0)->child(0)->returnsBool()) {
m_value->child(0) = m_value->child(0)->child(0);
m_changed = true;
}
TriState triState = m_value->child(0)->asTriState();
// Turn this: Branch(0, then, else)
// Into this: Jump(else)
if (triState == TriState::False) {
m_block->taken().block()->removePredecessor(m_block);
m_value->replaceWithJump(m_block, m_block->notTaken());
m_changedCFG = true;
break;
}
// Turn this: Branch(not 0, then, else)
// Into this: Jump(then)
if (triState == TriState::True) {
m_block->notTaken().block()->removePredecessor(m_block);
m_value->replaceWithJump(m_block, m_block->taken());
m_changedCFG = true;
break;
}
if (m_proc.optLevel() >= 2) {
// If a check for the same property dominates us, we can kill the branch. This sort
// of makes sense here because it's cheap, but hacks like this show that we're going
// to need SCCP.
Value* check = m_pureCSE.findMatch(
ValueKey(Check, Void, m_value->child(0)), m_block, *m_dominators);
if (check) {
// The Check would have side-exited if child(0) was non-zero. So, it must be
// zero here.
m_block->taken().block()->removePredecessor(m_block);
m_value->replaceWithJump(m_block, m_block->notTaken());
m_changedCFG = true;
}
}
break;
}
case Const32:
case Const64:
case ConstFloat:
case ConstDouble: {
ValueKey key = m_value->key();
if (Value* constInRoot = m_valueForConstant.get(key)) {
if (constInRoot != m_value) {
m_value->replaceWithIdentity(constInRoot);
m_changed = true;
}
} else if (m_block == m_root)
m_valueForConstant.add(key, m_value);
else {
Value* constInRoot = m_proc.clone(m_value);
ASSERT(m_root && m_root->size() >= 1);
m_root->appendNonTerminal(constInRoot);
m_valueForConstant.add(key, constInRoot);
m_value->replaceWithIdentity(constInRoot);
m_changed = true;
}
break;
}
default:
break;
}
}
// Find a node that:
// - functor(node) returns true.
// - it's reachable from the given node via children.
// - it's in the last "bound" slots in the current basic block.
// This algorithm is optimized under the assumption that the bound is small.
template<typename Functor>
Value* findRecentNodeMatching(Value* start, unsigned bound, const Functor& functor)
{
unsigned startIndex = bound < m_index ? m_index - bound : 0;
Value* result = nullptr;
start->walk(
[&] (Value* value) -> Value::WalkStatus {
bool found = false;
for (unsigned i = startIndex; i <= m_index; ++i) {
if (m_block->at(i) == value)
found = true;
}
if (!found)
return Value::IgnoreChildren;
if (functor(value)) {
result = value;
return Value::Stop;
}
return Value::Continue;
});
return result;
}
// This specializes a sequence of code up to a Select. This doesn't work when we're at a
// terminal. It would be cool to fix that eventually. The main problem is that instead of
// splitting the block, we should just insert the then/else blocks. We'll have to create
// double the Phis and double the Upsilons. It'll probably be the sort of optimization that
// we want to do only after we've done loop optimizations, since this will *definitely*
// obscure things. In fact, even this simpler form of select specialization will possibly
// obscure other optimizations. It would be great to have two modes of strength reduction,
// one that does obscuring optimizations and runs late, and another that does not do
// obscuring optimizations and runs early.
// FIXME: Make select specialization handle branches.
// FIXME: Have a form of strength reduction that does no obscuring optimizations and runs
// early.
void specializeSelect(Value* source)
{
if (B3ReduceStrengthInternal::verbose)
dataLog("Specializing select: ", deepDump(m_proc, source), "\n");
// This mutates startIndex to account for the fact that m_block got the front of it
// chopped off.
BasicBlock* predecessor = m_blockInsertionSet.splitForward(m_block, m_index, &m_insertionSet);
if (m_block == m_root) {
m_root = predecessor;
m_valueForConstant.clear();
}
// Splitting will commit the insertion set, which changes the exact position of the
// source. That's why we do the search after splitting.
unsigned startIndex = UINT_MAX;
for (unsigned i = predecessor->size(); i--;) {
if (predecessor->at(i) == source) {
startIndex = i;
break;
}
}
RELEASE_ASSERT(startIndex != UINT_MAX);
// By BasicBlock convention, caseIndex == 0 => then, caseIndex == 1 => else.
static constexpr unsigned numCases = 2;
BasicBlock* cases[numCases];
for (unsigned i = 0; i < numCases; ++i)
cases[i] = m_blockInsertionSet.insertBefore(m_block);
HashMap<Value*, Value*> mappings[2];
// Save things we want to know about the source.
Value* predicate = source->child(0);
for (unsigned i = 0; i < numCases; ++i)
mappings[i].add(source, source->child(1 + i));
auto cloneValue = [&] (Value* value) {
ASSERT(value != source);
for (unsigned i = 0; i < numCases; ++i) {
Value* clone = m_proc.clone(value);
for (Value*& child : clone->children()) {
if (Value* newChild = mappings[i].get(child))
child = newChild;
}
if (value->type() != Void)
mappings[i].add(value, clone);
cases[i]->append(clone);
if (value->type() != Void)
cases[i]->appendNew<UpsilonValue>(m_proc, value->origin(), clone, value);
}
value->replaceWithPhi();
};
// The jump that the splitter inserted is of no use to us.
predecessor->removeLast(m_proc);
// Hance the source, it's special.
for (unsigned i = 0; i < numCases; ++i) {
cases[i]->appendNew<UpsilonValue>(
m_proc, source->origin(), source->child(1 + i), source);
}
source->replaceWithPhi();
m_insertionSet.insertValue(m_index, source);
// Now handle all values between the source and the check.
for (unsigned i = startIndex + 1; i < predecessor->size(); ++i) {
Value* value = predecessor->at(i);
value->owner = nullptr;
cloneValue(value);
if (value->type() != Void)
m_insertionSet.insertValue(m_index, value);
else
m_proc.deleteValue(value);
}
// Finally, deal with the check.
cloneValue(m_value);
// Remove the values from the predecessor.
predecessor->values().resize(startIndex);
predecessor->appendNew<Value>(m_proc, Branch, source->origin(), predicate);
predecessor->setSuccessors(FrequentedBlock(cases[0]), FrequentedBlock(cases[1]));
for (unsigned i = 0; i < numCases; ++i) {
cases[i]->appendNew<Value>(m_proc, Jump, m_value->origin());
cases[i]->setSuccessors(FrequentedBlock(m_block));
}
m_changed = true;
predecessor->updatePredecessorsAfter();
}
static bool shouldSwapBinaryOperands(Value* value)
{
// Note that we have commutative operations that take more than two children. Those operations may
// commute their first two children while leaving the rest unaffected.
ASSERT(value->numChildren() >= 2);
// Leave it alone if the right child is a constant.
if (value->child(1)->isConstant()
|| value->child(0)->opcode() == AtomicStrongCAS)
return false;
if (value->child(0)->isConstant())
return true;
if (value->child(1)->opcode() == AtomicStrongCAS)
return true;
// Sort the operands. This is an important canonicalization. We use the index instead of
// the address to make this at least slightly deterministic.
if (value->child(0)->index() > value->child(1)->index())
return true;
return false;
}
// Turn this: Add(constant, value)
// Into this: Add(value, constant)
//
// Also:
// Turn this: Add(value1, value2)
// Into this: Add(value2, value1)
// If we decide that value2 coming first is the canonical ordering.
void handleCommutativity()
{
if (shouldSwapBinaryOperands(m_value)) {
std::swap(m_value->child(0), m_value->child(1));
m_changed = true;
}
}
// For Op==Add or Sub, turn any of these:
// Op(Mul(x1, x2), Mul(x1, x3))
// Op(Mul(x2, x1), Mul(x1, x3))
// Op(Mul(x1, x2), Mul(x3, x1))
// Op(Mul(x2, x1), Mul(x3, x1))
// Into this: Mul(x1, Op(x2, x3))
bool handleMulDistributivity()
{
ASSERT(m_value->opcode() == Add || m_value->opcode() == Sub);
Value* x1 = nullptr;
Value* x2 = nullptr;
Value* x3 = nullptr;
if (m_value->child(0)->opcode() == Mul && m_value->child(1)->opcode() == Mul) {
if (m_value->child(0)->child(0) == m_value->child(1)->child(0)) {
// Op(Mul(x1, x2), Mul(x1, x3))
x1 = m_value->child(0)->child(0);
x2 = m_value->child(0)->child(1);
x3 = m_value->child(1)->child(1);
} else if (m_value->child(0)->child(1) == m_value->child(1)->child(0)) {
// Op(Mul(x2, x1), Mul(x1, x3))
x1 = m_value->child(0)->child(1);
x2 = m_value->child(0)->child(0);
x3 = m_value->child(1)->child(1);
} else if (m_value->child(0)->child(0) == m_value->child(1)->child(1)) {
// Op(Mul(x1, x2), Mul(x3, x1))
x1 = m_value->child(0)->child(0);
x2 = m_value->child(0)->child(1);
x3 = m_value->child(1)->child(0);
} else if (m_value->child(0)->child(1) == m_value->child(1)->child(1)) {
// Op(Mul(x2, x1), Mul(x3, x1))
x1 = m_value->child(0)->child(1);
x2 = m_value->child(0)->child(0);
x3 = m_value->child(1)->child(0);
}
}
if (x1 != nullptr) {
ASSERT(x2 != nullptr && x3 != nullptr);
Value* newOp = m_insertionSet.insert<Value>(m_index, m_value->opcode(), m_value->origin(), x2, x3);
replaceWithNew<Value>(Mul, m_value->origin(), x1, newOp);
return true;
}
return false;
}
// For Op==BitOr or BitXor, turn any of these:
// Op(BitAnd(x1, x2), BitAnd(x1, x3))
// Op(BitAnd(x2, x1), BitAnd(x1, x3))
// Op(BitAnd(x1, x2), BitAnd(x3, x1))
// Op(BitAnd(x2, x1), BitAnd(x3, x1))
// Into this: BitAnd(Op(x2, x3), x1)
// And any of these:
// Op(BitAnd(x1, x2), x1)
// Op(BitAnd(x2, x1), x1)
// Op(x1, BitAnd(x1, x2))
// Op(x1, BitAnd(x2, x1))
// Into this: BitAnd(Op(x2, x1), x1)
// This second set is equivalent to doing x1 => BitAnd(x1, x1), and then applying the first set.
// It does not reduce the number of operations executed, but provides some useful normalization: we prefer to have BitAnd at the outermost, then BitXor, and finally BitOr at the innermost
bool handleBitAndDistributivity()
{
ASSERT(m_value->opcode() == BitOr || m_value->opcode() == BitXor);
Value* x1 = nullptr;
Value* x2 = nullptr;
Value* x3 = nullptr;
if (m_value->child(0)->opcode() == BitAnd && m_value->child(1)->opcode() == BitAnd) {
if (m_value->child(0)->child(0) == m_value->child(1)->child(0)) {
x1 = m_value->child(0)->child(0);
x2 = m_value->child(0)->child(1);
x3 = m_value->child(1)->child(1);
} else if (m_value->child(0)->child(1) == m_value->child(1)->child(0)) {
x1 = m_value->child(0)->child(1);
x2 = m_value->child(0)->child(0);
x3 = m_value->child(1)->child(1);
} else if (m_value->child(0)->child(0) == m_value->child(1)->child(1)) {
x1 = m_value->child(0)->child(0);
x2 = m_value->child(0)->child(1);
x3 = m_value->child(1)->child(0);
} else if (m_value->child(0)->child(1) == m_value->child(1)->child(1)) {
x1 = m_value->child(0)->child(1);
x2 = m_value->child(0)->child(0);
x3 = m_value->child(1)->child(0);
}
} else if (m_value->child(0)->opcode() == BitAnd) {
if (m_value->child(0)->child(0) == m_value->child(1)) {
x1 = x3 = m_value->child(1);
x2 = m_value->child(0)->child(1);
} else if (m_value->child(0)->child(1) == m_value->child(1)) {
x1 = x3 = m_value->child(1);
x2 = m_value->child(0)->child(0);
}
} else if (m_value->child(1)->opcode() == BitAnd) {
if (m_value->child(1)->child(0) == m_value->child(0)) {
x1 = x3 = m_value->child(0);
x2 = m_value->child(1)->child(1);
} else if (m_value->child(1)->child(1) == m_value->child(0)) {
x1 = x3 = m_value->child(0);
x2 = m_value->child(1)->child(0);
}
}
if (x1 != nullptr) {
ASSERT(x2 != nullptr && x3 != nullptr);
Value* bitOp = m_insertionSet.insert<Value>(m_index, m_value->opcode(), m_value->origin(), x2, x3);
replaceWithNew<Value>(BitAnd, m_value->origin(), x1, bitOp);
return true;
}
return false;
}
struct CanonicalizedComparison {
Opcode opcode;
Value* operands[2];
};
static CanonicalizedComparison canonicalizeComparison(Value* value)
{
auto flip = [] (Opcode opcode) {
switch (opcode) {
case LessThan:
return GreaterThan;
case GreaterThan:
return LessThan;
case LessEqual:
return GreaterEqual;
case GreaterEqual:
return LessEqual;
case Above:
return Below;
case Below:
return Above;
case AboveEqual:
return BelowEqual;
case BelowEqual:
return AboveEqual;
default:
return opcode;
}
};
if (shouldSwapBinaryOperands(value))
return { flip(value->opcode()), { value->child(1), value->child(0) } };
return { value->opcode(), { value->child(0), value->child(1) } };
}
// FIXME: This should really be a forward analysis. Instead, we uses a bounded-search backwards
// analysis.
IntRange rangeFor(Value* value, unsigned timeToLive = 5)
{
if (!timeToLive)
return IntRange::top(value->type());
switch (value->opcode()) {
case Const32:
case Const64: {
int64_t intValue = value->asInt();
return IntRange(intValue, intValue);
}
case BitAnd:
if (value->child(1)->hasInt())
return IntRange::rangeForMask(value->child(1)->asInt(), value->type());
break;
case SShr:
if (value->child(1)->hasInt32()) {
return rangeFor(value->child(0), timeToLive - 1).sShr(
value->child(1)->asInt32(), value->type());
}
break;
case ZShr:
if (value->child(1)->hasInt32()) {
return rangeFor(value->child(0), timeToLive - 1).zShr(
value->child(1)->asInt32(), value->type());
}
break;
case Shl:
if (value->child(1)->hasInt32()) {
return rangeFor(value->child(0), timeToLive - 1).shl(
value->child(1)->asInt32(), value->type());
}
break;
case Add:
return rangeFor(value->child(0), timeToLive - 1).add(
rangeFor(value->child(1), timeToLive - 1), value->type());
case Sub:
return rangeFor(value->child(0), timeToLive - 1).sub(
rangeFor(value->child(1), timeToLive - 1), value->type());
case Mul:
return rangeFor(value->child(0), timeToLive - 1).mul(
rangeFor(value->child(1), timeToLive - 1), value->type());
case SExt8:
case SExt16:
case SExt32:
return rangeFor(value->child(0), timeToLive - 1);
case ZExt32:
return rangeFor(value->child(0), timeToLive - 1).zExt32();
default:
break;
}
return IntRange::top(value->type());
}
template<typename ValueType, typename... Arguments>
void replaceWithNew(Arguments... arguments)
{
replaceWithNewValue(m_proc.add<ValueType>(arguments...));
}
bool replaceWithNewValue(Value* newValue)
{
if (!newValue)
return false;
m_insertionSet.insertValue(m_index, newValue);
m_value->replaceWithIdentity(newValue);
m_changed = true;
return true;
}
void replaceWithIdentity(Value* newValue)
{
m_value->replaceWithIdentity(newValue);
m_changed = true;
}
void handleShiftAmount()
{
// Shift anything by zero is identity.
if (m_value->child(1)->isInt32(0)) {
replaceWithIdentity(m_value->child(0));
return;
}
// The shift already masks its shift amount. If the shift amount is being masked by a
// redundant amount, then remove the mask. For example,
// Turn this: Shl(@x, BitAnd(@y, 63))
// Into this: Shl(@x, @y)
unsigned mask = sizeofType(m_value->type()) * 8 - 1;
if (m_value->child(1)->opcode() == BitAnd
&& m_value->child(1)->child(1)->hasInt32()
&& (m_value->child(1)->child(1)->asInt32() & mask) == mask) {
m_value->child(1) = m_value->child(1)->child(0);
m_changed = true;
}
}
void replaceIfRedundant()
{
m_changed |= m_pureCSE.process(m_value, *m_dominators);
}
void simplifyCFG()
{
if (B3ReduceStrengthInternal::verbose) {
dataLog("Before simplifyCFG:\n");
dataLog(m_proc);
}
// We have three easy simplification rules:
//
// 1) If a successor is a block that just jumps to another block, then jump directly to
// that block.
//
// 2) If all successors are the same and the operation has no effects, then use a jump
// instead.
//
// 3) If you jump to a block that is not you and has one predecessor, then merge.
//
// Note that because of the first rule, this phase may introduce critical edges. That's fine.
// If you need broken critical edges, then you have to break them yourself.
// Note that this relies on predecessors being at least conservatively correct. It's fine for
// predecessors to mention a block that isn't actually a predecessor. It's *not* fine for a
// predecessor to be omitted. We assert as much in the loop. In practice, we precisely preserve
// predecessors during strength reduction since that minimizes the total number of fixpoint
// iterations needed to kill a lot of code.
for (BasicBlock* block : m_proc.blocksInPostOrder()) {
if (B3ReduceStrengthInternal::verbose)
dataLog("Considering block ", *block, ":\n");
checkPredecessorValidity();
// We don't care about blocks that don't have successors.
if (!block->numSuccessors())
continue;
// First check if any of the successors of this block can be forwarded over.
for (BasicBlock*& successor : block->successorBlocks()) {
if (successor != block
&& successor->size() == 1
&& successor->last()->opcode() == Jump) {
BasicBlock* newSuccessor = successor->successorBlock(0);
if (newSuccessor != successor) {
if (B3ReduceStrengthInternal::verbose) {
dataLog(
"Replacing ", pointerDump(block), "->", pointerDump(successor),
" with ", pointerDump(block), "->", pointerDump(newSuccessor),
"\n");
}
// Note that we do not do replacePredecessor() because the block we're
// skipping will still have newSuccessor as its successor.
newSuccessor->addPredecessor(block);
successor = newSuccessor;
m_changedCFG = true;
}
}
}
// Now check if the block's terminal can be replaced with a jump.
if (block->numSuccessors() > 1) {
// The terminal must not have weird effects.
Effects effects = block->last()->effects();
effects.terminal = false;
if (!effects.mustExecute()) {
// All of the successors must be the same.
bool allSame = true;
BasicBlock* firstSuccessor = block->successorBlock(0);
for (unsigned i = 1; i < block->numSuccessors(); ++i) {
if (block->successorBlock(i) != firstSuccessor) {
allSame = false;
break;
}
}
if (allSame) {
if (B3ReduceStrengthInternal::verbose) {
dataLog(
"Changing ", pointerDump(block), "'s terminal to a Jump.\n");
}
block->last()->replaceWithJump(block, FrequentedBlock(firstSuccessor));
m_changedCFG = true;
}
}
}
// Finally handle jumps to a block with one predecessor.
if (block->numSuccessors() == 1) {
BasicBlock* successor = block->successorBlock(0);
if (successor != block && successor->numPredecessors() == 1) {
RELEASE_ASSERT(successor->predecessor(0) == block);
// We can merge the two blocks, because the predecessor only jumps to the successor
// and the successor is only reachable from the predecessor.
// Remove the terminal.
Value* value = block->values().takeLast();
Origin jumpOrigin = value->origin();
RELEASE_ASSERT(value->effects().terminal);
m_proc.deleteValue(value);
// Append the full contents of the successor to the predecessor.
block->values().appendVector(successor->values());
block->successors() = successor->successors();
// Make sure that the successor has nothing left in it. Make sure that the block
// has a terminal so that nobody chokes when they look at it.
successor->values().shrink(0);
successor->appendNew<Value>(m_proc, Oops, jumpOrigin);
successor->clearSuccessors();
// Ensure that predecessors of block's new successors know what's up.
for (BasicBlock* newSuccessor : block->successorBlocks())
newSuccessor->replacePredecessor(successor, block);
if (B3ReduceStrengthInternal::verbose) {
dataLog(
"Merged ", pointerDump(block), "->", pointerDump(successor), "\n");
}
m_changedCFG = true;
}
}
}
if (m_changedCFG && B3ReduceStrengthInternal::verbose) {
dataLog("B3 after simplifyCFG:\n");
dataLog(m_proc);
}
}
void handleChangedCFGIfNecessary()
{
if (m_changedCFG) {
m_proc.resetReachability();
m_proc.invalidateCFG();
m_dominators = nullptr; // Dominators are not valid anymore, and we don't need them yet.
m_changed = true;
}
}
void checkPredecessorValidity()
{
if (!shouldValidateIRAtEachPhase())
return;
for (BasicBlock* block : m_proc) {
for (BasicBlock* successor : block->successorBlocks())
RELEASE_ASSERT(successor->containsPredecessor(block));
}
}
void simplifySSA()
{
// This runs Aycock and Horspool's algorithm on our Phi functions [1]. For most CFG patterns,
// this can take a suboptimal arrangement of Phi functions and make it optimal, as if you had
// run Cytron, Ferrante, Rosen, Wegman, and Zadeck. It's only suboptimal for irreducible
// CFGs. In practice, that doesn't matter, since we expect clients of B3 to run their own SSA
// conversion before lowering to B3, and in the case of the DFG, that conversion uses Cytron
// et al. In that context, this algorithm is intended to simplify Phi functions that were
// made redundant by prior CFG simplification. But according to Aycock and Horspool's paper,
// this algorithm is good enough that a B3 client could just give us maximal Phi's (i.e. Phi
// for each variable at each basic block) and we will make them optimal.
// [1] http://pages.cpsc.ucalgary.ca/~aycock/papers/ssa.ps
// Aycock and Horspool prescribe two rules that are to be run to fixpoint:
//
// 1) If all of the Phi's children are the same (i.e. it's one child referenced from one or
// more Upsilons), then replace all uses of the Phi with the one child.
//
// 2) If all of the Phi's children are either the Phi itself or exactly one other child, then
// replace all uses of the Phi with the one other child.
//
// Rule (2) subsumes rule (1), so we can just run (2). We only run one fixpoint iteration
// here. This premise is that in common cases, this will only find optimization opportunities
// as a result of CFG simplification and usually CFG simplification will only do one round
// of block merging per ReduceStrength fixpoint iteration, so it's OK for this to only do one
// round of Phi merging - since Phis are the value analogue of blocks.
PhiChildren phiChildren(m_proc);
for (Value* phi : phiChildren.phis()) {
Value* otherChild = nullptr;
bool ok = true;
for (Value* child : phiChildren[phi].values()) {
if (child == phi)
continue;
if (child == otherChild)
continue;
if (!otherChild) {
otherChild = child;
continue;
}
ok = false;
break;
}
if (!ok)
continue;
if (!otherChild) {
// Wow, this would be super weird. It probably won't happen, except that things could
// get weird as a consequence of stepwise simplifications in the strength reduction
// fixpoint.
continue;
}
// Turn the Phi into an Identity and turn the Upsilons into Nops.
m_changed = true;
for (Value* upsilon : phiChildren[phi])
upsilon->replaceWithNop();
phi->replaceWithIdentity(otherChild);
}
}
Procedure& m_proc;
InsertionSet m_insertionSet;
BlockInsertionSet m_blockInsertionSet;
HashMap<ValueKey, Value*> m_valueForConstant;
BasicBlock* m_root { nullptr };
BasicBlock* m_block { nullptr };
unsigned m_index { 0 };
Value* m_value { nullptr };
Dominators* m_dominators { nullptr };
PureCSE m_pureCSE;
bool m_changed { false };
bool m_changedCFG { false };
};
} // anonymous namespace
bool reduceStrength(Procedure& proc)
{
PhaseScope phaseScope(proc, "reduceStrength");
ReduceStrength reduceStrength(proc);
return reduceStrength.run();
}
} } // namespace JSC::B3
#endif // ENABLE(B3_JIT)