--- /dev/null
+//===--------- 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.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/AssumptionCache.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/Utils/Local.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "loop-simplifycfg"
+
+namespace {
+class LoopSimplifyCFG : public LoopPass {
+public:
+ static char ID; // Pass ID, replacement for typeid
+ LoopSimplifyCFG() : LoopPass(ID) {
+ initializeLoopSimplifyCFGPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnLoop(Loop *L, LPPassManager &) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<LoopInfoWrapperPass>();
+
+ AU.addPreserved<DominatorTreeWrapperPass>();
+ AU.addPreserved<LoopInfoWrapperPass>();
+ AU.addPreserved<GlobalsAAWrapperPass>();
+ AU.addPreserved<BasicAAWrapperPass>();
+ AU.addPreserved<AAResultsWrapperPass>();
+ AU.addPreserved<ScalarEvolutionWrapperPass>();
+ AU.addPreserved<SCEVAAWrapperPass>();
+ AU.addPreserved<DependenceAnalysis>();
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addPreservedID(LCSSAID);
+ }
+};
+}
+
+char LoopSimplifyCFG::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
+ false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_END(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
+ false, false)
+
+Pass *llvm::createLoopSimplifyCFGPass() { return new LoopSimplifyCFG(); }
+
+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<WeakVH, 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<BasicBlock>(Block);
+ if (!Succ)
+ continue;
+
+ BasicBlock *Pred = Succ->getSinglePredecessor();
+ if (!Pred || !Pred->getSingleSuccessor() || LI->getLoopFor(Pred) != L)
+ continue;
+
+ // Pred is going to disappear, so we need to update the loop info.
+ if (L->getHeader() == Pred)
+ L->moveToHeader(Succ);
+ LI->removeBlock(Pred);
+ MergeBasicBlockIntoOnlyPred(Succ, DT);
+ Changed = true;
+ }
+
+ return Changed;
+}
+
+/// runOnLoop - Perform basic CFG simplifications to assist other loop passes.
+/// For now, this only attempts to merge blocks in the trivial case.
+bool LoopSimplifyCFG::runOnLoop(Loop *L, LPPassManager &) {
+ if (skipOptnoneFunction(L))
+ return false;
+
+ DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ return simplifyLoopCFG(L, DT, LI);
+}