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//===--------- LoopSimplifyCFG.cpp - Loop CFG Simplification Pass ---------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file implements the Loop SimplifyCFG Pass. This pass is responsible for
// basic loop CFG cleanup, primarily to assist other loop passes. If you
// encounter a noncanonical CFG construct that causes another loop pass to
// perform suboptimally, this is the place to fix it up.
#include "llvm/Transforms/Scalar/LoopSimplifyCFG.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/DependenceAnalysis.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/LoopPassManager.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
using namespace llvm;
#define DEBUG_TYPE "loop-simplifycfg"
static bool simplifyLoopCFG(Loop &L, DominatorTree &DT, LoopInfo &LI) {
bool Changed = false;
// Copy blocks into a temporary array to avoid iterator invalidation issues
// as we remove them.
SmallVector<WeakTrackingVH, 16> Blocks(L.blocks());
for (auto &Block : Blocks) {
// Attempt to merge blocks in the trivial case. Don't modify blocks which
// belong to other loops.
BasicBlock *Succ = cast_or_null<BasicBlock>(Block);
if (!Succ)
BasicBlock *Pred = Succ->getSinglePredecessor();
if (!Pred || !Pred->getSingleSuccessor() || LI.getLoopFor(Pred) != &L)
// Pred is going to disappear, so we need to update the loop info.
if (L.getHeader() == Pred)
MergeBasicBlockIntoOnlyPred(Succ, &DT);
Changed = true;
return Changed;
PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
LPMUpdater &) {
if (!simplifyLoopCFG(L, AR.DT, AR.LI))
return PreservedAnalyses::all();
return getLoopPassPreservedAnalyses();
namespace {
class LoopSimplifyCFGLegacyPass : public LoopPass {
static char ID; // Pass ID, replacement for typeid
LoopSimplifyCFGLegacyPass() : LoopPass(ID) {
bool runOnLoop(Loop *L, LPPassManager &) override {
if (skipLoop(L))
return false;
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
return simplifyLoopCFG(*L, DT, LI);
void getAnalysisUsage(AnalysisUsage &AU) const override {
char LoopSimplifyCFGLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
"Simplify loop CFG", false, false)
INITIALIZE_PASS_END(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
"Simplify loop CFG", false, false)
Pass *llvm::createLoopSimplifyCFGPass() {
return new LoopSimplifyCFGLegacyPass();