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//===-- NVPTXPrologEpilogPass.cpp - NVPTX prolog/epilog inserter ----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file is a copy of the generic LLVM PrologEpilogInserter pass, modified
// to remove unneeded functionality and to handle virtual registers. Most code
// here is a copy of PrologEpilogInserter.cpp.
//
//===----------------------------------------------------------------------===//
#include "NVPTX.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "nvptx-prolog-epilog"
namespace {
class NVPTXPrologEpilogPass : public MachineFunctionPass {
public:
static char ID;
NVPTXPrologEpilogPass() : MachineFunctionPass(ID) {}
bool runOnMachineFunction(MachineFunction &MF) override;
private:
void calculateFrameObjectOffsets(MachineFunction &Fn);
};
}
MachineFunctionPass *llvm::createNVPTXPrologEpilogPass() {
return new NVPTXPrologEpilogPass();
}
char NVPTXPrologEpilogPass::ID = 0;
bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
const TargetSubtargetInfo &STI = MF.getSubtarget();
const TargetFrameLowering &TFI = *STI.getFrameLowering();
const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
bool Modified = false;
calculateFrameObjectOffsets(MF);
for (MachineBasicBlock &MBB : MF) {
for (MachineInstr &MI : MBB) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
if (!MI.getOperand(i).isFI())
continue;
// Frame indices in debug values are encoded in a target independent
// way with simply the frame index and offset rather than any
// target-specific addressing mode.
if (MI.isDebugValue()) {
assert(i == 0 && "Frame indices can only appear as the first "
"operand of a DBG_VALUE machine instruction");
unsigned Reg;
int64_t Offset =
TFI.getFrameIndexReference(MF, MI.getOperand(0).getIndex(), Reg);
MI.getOperand(0).ChangeToRegister(Reg, /*isDef=*/false);
MI.getOperand(0).setIsDebug();
auto *DIExpr = DIExpression::prepend(
MI.getDebugExpression(), DIExpression::ApplyOffset, Offset);
MI.getOperand(3).setMetadata(DIExpr);
continue;
}
TRI.eliminateFrameIndex(MI, 0, i, nullptr);
Modified = true;
}
}
}
// Add function prolog/epilog
TFI.emitPrologue(MF, MF.front());
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
// If last instruction is a return instruction, add an epilogue
if (I->isReturnBlock())
TFI.emitEpilogue(MF, *I);
}
return Modified;
}
/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
static inline void
AdjustStackOffset(MachineFrameInfo &MFI, int FrameIdx,
bool StackGrowsDown, int64_t &Offset,
unsigned &MaxAlign) {
// If the stack grows down, add the object size to find the lowest address.
if (StackGrowsDown)
Offset += MFI.getObjectSize(FrameIdx);
unsigned Align = MFI.getObjectAlignment(FrameIdx);
// If the alignment of this object is greater than that of the stack, then
// increase the stack alignment to match.
MaxAlign = std::max(MaxAlign, Align);
// Adjust to alignment boundary.
Offset = (Offset + Align - 1) / Align * Align;
if (StackGrowsDown) {
LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset
<< "]\n");
MFI.setObjectOffset(FrameIdx, -Offset); // Set the computed offset
} else {
LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset
<< "]\n");
MFI.setObjectOffset(FrameIdx, Offset);
Offset += MFI.getObjectSize(FrameIdx);
}
}
void
NVPTXPrologEpilogPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
bool StackGrowsDown =
TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
// Loop over all of the stack objects, assigning sequential addresses...
MachineFrameInfo &MFI = Fn.getFrameInfo();
// Start at the beginning of the local area.
// The Offset is the distance from the stack top in the direction
// of stack growth -- so it's always nonnegative.
int LocalAreaOffset = TFI.getOffsetOfLocalArea();
if (StackGrowsDown)
LocalAreaOffset = -LocalAreaOffset;
assert(LocalAreaOffset >= 0
&& "Local area offset should be in direction of stack growth");
int64_t Offset = LocalAreaOffset;
// If there are fixed sized objects that are preallocated in the local area,
// non-fixed objects can't be allocated right at the start of local area.
// We currently don't support filling in holes in between fixed sized
// objects, so we adjust 'Offset' to point to the end of last fixed sized
// preallocated object.
for (int i = MFI.getObjectIndexBegin(); i != 0; ++i) {
int64_t FixedOff;
if (StackGrowsDown) {
// The maximum distance from the stack pointer is at lower address of
// the object -- which is given by offset. For down growing stack
// the offset is negative, so we negate the offset to get the distance.
FixedOff = -MFI.getObjectOffset(i);
} else {
// The maximum distance from the start pointer is at the upper
// address of the object.
FixedOff = MFI.getObjectOffset(i) + MFI.getObjectSize(i);
}
if (FixedOff > Offset) Offset = FixedOff;
}
// NOTE: We do not have a call stack
unsigned MaxAlign = MFI.getMaxAlignment();
// No scavenger
// FIXME: Once this is working, then enable flag will change to a target
// check for whether the frame is large enough to want to use virtual
// frame index registers. Functions which don't want/need this optimization
// will continue to use the existing code path.
if (MFI.getUseLocalStackAllocationBlock()) {
unsigned Align = MFI.getLocalFrameMaxAlign();
// Adjust to alignment boundary.
Offset = (Offset + Align - 1) / Align * Align;
LLVM_DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
// Resolve offsets for objects in the local block.
for (unsigned i = 0, e = MFI.getLocalFrameObjectCount(); i != e; ++i) {
std::pair<int, int64_t> Entry = MFI.getLocalFrameObjectMap(i);
int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
LLVM_DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" << FIOffset
<< "]\n");
MFI.setObjectOffset(Entry.first, FIOffset);
}
// Allocate the local block
Offset += MFI.getLocalFrameSize();
MaxAlign = std::max(Align, MaxAlign);
}
// No stack protector
// Then assign frame offsets to stack objects that are not used to spill
// callee saved registers.
for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
if (MFI.isObjectPreAllocated(i) &&
MFI.getUseLocalStackAllocationBlock())
continue;
if (MFI.isDeadObjectIndex(i))
continue;
AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
}
// No scavenger
if (!TFI.targetHandlesStackFrameRounding()) {
// If we have reserved argument space for call sites in the function
// immediately on entry to the current function, count it as part of the
// overall stack size.
if (MFI.adjustsStack() && TFI.hasReservedCallFrame(Fn))
Offset += MFI.getMaxCallFrameSize();
// Round up the size to a multiple of the alignment. If the function has
// any calls or alloca's, align to the target's StackAlignment value to
// ensure that the callee's frame or the alloca data is suitably aligned;
// otherwise, for leaf functions, align to the TransientStackAlignment
// value.
unsigned StackAlign;
if (MFI.adjustsStack() || MFI.hasVarSizedObjects() ||
(RegInfo->needsStackRealignment(Fn) && MFI.getObjectIndexEnd() != 0))
StackAlign = TFI.getStackAlignment();
else
StackAlign = TFI.getTransientStackAlignment();
// If the frame pointer is eliminated, all frame offsets will be relative to
// SP not FP. Align to MaxAlign so this works.
StackAlign = std::max(StackAlign, MaxAlign);
unsigned AlignMask = StackAlign - 1;
Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
}
// Update frame info to pretend that this is part of the stack...
int64_t StackSize = Offset - LocalAreaOffset;
MFI.setStackSize(StackSize);
}