[JumpThreading] Thread through guards

Summary:
This patch allows JumpThreading also thread through guards.
Virtually, guard(cond) is equivalent to the following construction:

  if (cond) { do something } else {deoptimize}

Yet it is not explicitly converted into IFs before lowering.
This patch enables early threading through guards in simple cases.
Currently it covers the following situation:

  if (cond1) {
    // code A
  } else {
    // code B
  }
  // code C
  guard(cond2)
  // code D

If there is implication cond1 => cond2 or !cond1 => cond2, we can transform
this construction into the following:

  if (cond1) {
    // code A
    // code C
  } else {
    // code B
    // code C
    guard(cond2)
  }
  // code D

Thus, removing the guard from one of execution branches.

Patch by Max Kazantsev!

Reviewers: reames, apilipenko, igor-laevsky, anna, sanjoy

Reviewed By: sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D29620

llvm-svn: 294617

1 files changed, 47 insertions, 0 deletions

diff --git a/llvm/unittests/Transforms/Utils/Cloning.cpp b/llvm/unittests/Transforms/Utils/Cloning.cpp
index 634aa9e7e65..a216959751f 100644
--- a/llvm/unittests/Transforms/Utils/Cloning.cpp
+++ b/llvm/unittests/Transforms/Utils/Cloning.cpp
@@ -201,6 +201,53 @@ TEST_F(CloneInstruction, CallingConvention) {
   delete F2;
 }
 
+TEST_F(CloneInstruction, DuplicateInstructionsToSplit) {
+  Type *ArgTy1[] = {Type::getInt32PtrTy(context)};
+  FunctionType *FT = FunctionType::get(Type::getVoidTy(context), ArgTy1, false);
+  V = new Argument(Type::getInt32Ty(context));
+
+  Function *F = Function::Create(FT, Function::ExternalLinkage);
+
+  BasicBlock *BB1 = BasicBlock::Create(context, "", F);
+  IRBuilder<> Builder1(BB1);
+
+  BasicBlock *BB2 = BasicBlock::Create(context, "", F);
+  IRBuilder<> Builder2(BB2);
+
+  Builder1.CreateBr(BB2);
+
+  Instruction *AddInst = cast<Instruction>(Builder2.CreateAdd(V, V));
+  Instruction *MulInst = cast<Instruction>(Builder2.CreateMul(AddInst, V));
+  Instruction *SubInst = cast<Instruction>(Builder2.CreateSub(MulInst, V));
+  Builder2.CreateRetVoid();
+
+  ValueToValueMapTy Mapping;
+
+  auto Split = DuplicateInstructionsInSplitBetween(BB2, BB1, SubInst, Mapping);
+
+  EXPECT_TRUE(Split);
+  EXPECT_EQ(Mapping.size(), 2u);
+  EXPECT_TRUE(Mapping.find(AddInst) != Mapping.end());
+  EXPECT_TRUE(Mapping.find(MulInst) != Mapping.end());
+
+  auto AddSplit = dyn_cast<Instruction>(Mapping[AddInst]);
+  EXPECT_TRUE(AddSplit);
+  EXPECT_EQ(AddSplit->getOperand(0), V);
+  EXPECT_EQ(AddSplit->getOperand(1), V);
+  EXPECT_EQ(AddSplit->getParent(), Split);
+
+  auto MulSplit = dyn_cast<Instruction>(Mapping[MulInst]);
+  EXPECT_TRUE(MulSplit);
+  EXPECT_EQ(MulSplit->getOperand(0), AddSplit);
+  EXPECT_EQ(MulSplit->getOperand(1), V);
+  EXPECT_EQ(MulSplit->getParent(), Split);
+
+  EXPECT_EQ(AddSplit->getNextNode(), MulSplit);
+  EXPECT_EQ(MulSplit->getNextNode(), Split->getTerminator());
+
+  delete F;
+}
+
 class CloneFunc : public ::testing::Test {
 protected:
   void SetUp() override {