1 files changed, 114 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
new file mode 100644
index 000000000000..ec227932c09e
--- /dev/null
+++ b/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -0,0 +1,114 @@
+//===--------- 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/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/LoopPassManager.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/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<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_or_null<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;
+}
+
+PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, AnalysisManager<Loop> &AM) {
+  const auto &FAM =
+      AM.getResult<FunctionAnalysisManagerLoopProxy>(L).getManager();
+  Function *F = L.getHeader()->getParent();
+
+  auto *LI = FAM.getCachedResult<LoopAnalysis>(*F);
+  auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(*F);
+  assert((LI && DT) && "Analyses for LoopSimplifyCFG not available");
+
+  if (!simplifyLoopCFG(L, *DT, *LI))
+    return PreservedAnalyses::all();
+  return getLoopPassPreservedAnalyses();
+}
+
+namespace {
+class LoopSimplifyCFGLegacyPass : public LoopPass {
+public:
+  static char ID; // Pass ID, replacement for typeid
+  LoopSimplifyCFGLegacyPass() : LoopPass(ID) {
+    initializeLoopSimplifyCFGLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  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 {
+    AU.addPreserved<DependenceAnalysisWrapperPass>();
+    getLoopAnalysisUsage(AU);
+  }
+};
+}
+
+char LoopSimplifyCFGLegacyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
+                      "Simplify loop CFG", false, false)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
+INITIALIZE_PASS_END(LoopSimplifyCFGLegacyPass, "loop-simplifycfg",
+                    "Simplify loop CFG", false, false)
+
+Pass *llvm::createLoopSimplifyCFGPass() {
+  return new LoopSimplifyCFGLegacyPass();
+}