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a function's CFG when that CFG is unchanged. This allows transformation passes to simply claim they preserve the CFG and analysis passes to check for the CFG being preserved to remove the fanout of all analyses being listed in all passes. I've gone through and removed or cleaned up as many of the comments reminding us to do this as I could. Differential Revision: https://reviews.llvm.org/D28627 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292054 91177308-0d34-0410-b5e6-96231b3b80d8
110 lines
3.8 KiB
C++
110 lines
3.8 KiB
C++
//===--------- LoopSimplifyCFG.cpp - Loop CFG Simplification Pass ---------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the Loop SimplifyCFG Pass. This pass is responsible for
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// basic loop CFG cleanup, primarily to assist other loop passes. If you
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// encounter a noncanonical CFG construct that causes another loop pass to
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// perform suboptimally, this is the place to fix it up.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/LoopSimplifyCFG.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/BasicAliasAnalysis.h"
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#include "llvm/Analysis/DependenceAnalysis.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Scalar/LoopPassManager.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/LoopUtils.h"
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using namespace llvm;
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#define DEBUG_TYPE "loop-simplifycfg"
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static bool simplifyLoopCFG(Loop &L, DominatorTree &DT, LoopInfo &LI) {
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bool Changed = false;
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// Copy blocks into a temporary array to avoid iterator invalidation issues
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// as we remove them.
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SmallVector<WeakVH, 16> Blocks(L.blocks());
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for (auto &Block : Blocks) {
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// Attempt to merge blocks in the trivial case. Don't modify blocks which
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// belong to other loops.
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BasicBlock *Succ = cast_or_null<BasicBlock>(Block);
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if (!Succ)
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continue;
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BasicBlock *Pred = Succ->getSinglePredecessor();
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if (!Pred || !Pred->getSingleSuccessor() || LI.getLoopFor(Pred) != &L)
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continue;
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// Pred is going to disappear, so we need to update the loop info.
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if (L.getHeader() == Pred)
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L.moveToHeader(Succ);
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LI.removeBlock(Pred);
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MergeBasicBlockIntoOnlyPred(Succ, &DT);
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Changed = true;
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}
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return Changed;
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}
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PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, LoopAnalysisManager &AM,
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LoopStandardAnalysisResults &AR,
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LPMUpdater &) {
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if (!simplifyLoopCFG(L, AR.DT, AR.LI))
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return PreservedAnalyses::all();
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return getLoopPassPreservedAnalyses();
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}
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namespace {
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class LoopSimplifyCFGLegacyPass : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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LoopSimplifyCFGLegacyPass() : LoopPass(ID) {
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initializeLoopSimplifyCFGLegacyPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop *L, LPPassManager &) override {
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if (skipLoop(L))
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return false;
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DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
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return simplifyLoopCFG(*L, DT, LI);
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addPreserved<DependenceAnalysisWrapperPass>();
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getLoopAnalysisUsage(AU);
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}
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};
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}
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char LoopSimplifyCFGLegacyPass::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
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"Simplify loop CFG", false, false)
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INITIALIZE_PASS_DEPENDENCY(LoopPass)
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INITIALIZE_PASS_END(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
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"Simplify loop CFG", false, false)
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Pass *llvm::createLoopSimplifyCFGPass() {
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return new LoopSimplifyCFGLegacyPass();
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}
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