Add InstCombine/InstructionSimplify support for Freeze Instruction
Summary:
- Add llvm::SimplifyFreezeInst
- Add InstCombiner::visitFreeze
- Add llvm tests
Reviewers: majnemer, sanjoy, reames, lebedev.ri, spatel
Reviewed By: reames, lebedev.ri
Subscribers: reames, lebedev.ri, filcab, regehr, trentxintong, llvm-commits
Differential Revision: https://reviews.llvm.org/D29013
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 83b767a..3ef8f9b00 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5241,6 +5241,19 @@
return ConstantFoldCall(Call, F, ConstantArgs, Q.TLI);
}
+/// Given operands for a Freeze, see if we can fold the result.
+static Value *SimplifyFreezeInst(Value *Op0) {
+ // Use a utility function defined in ValueTracking.
+ if (llvm::isGuaranteedNotToBeUndefOrPoison(Op0))
+ return Op0;
+ // We have room for improvement.
+ return nullptr;
+}
+
+Value *llvm::SimplifyFreezeInst(Value *Op0, const SimplifyQuery &Q) {
+ return ::SimplifyFreezeInst(Op0);
+}
+
/// See if we can compute a simplified version of this instruction.
/// If not, this returns null.
@@ -5383,6 +5396,9 @@
Result = SimplifyCall(cast<CallInst>(I), Q);
break;
}
+ case Instruction::Freeze:
+ Result = SimplifyFreezeInst(I->getOperand(0), Q);
+ break;
#define HANDLE_CAST_INST(num, opc, clas) case Instruction::opc:
#include "llvm/IR/Instruction.def"
#undef HANDLE_CAST_INST
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index cc5acf5..b26c629 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4221,6 +4221,20 @@
return llvm::any_of(GuardingBranches, AllUsesGuardedByBranch);
}
+bool llvm::isGuaranteedNotToBeUndefOrPoison(const Value *V) {
+ // If the value is a freeze instruction, then it can never
+ // be undef or poison.
+ if (isa<FreezeInst>(V))
+ return true;
+ // TODO: Some instructions are guaranteed to return neither undef
+ // nor poison if their arguments are not poison/undef.
+
+ // TODO: Deal with other Constant subclasses.
+ if (isa<ConstantInt>(V) || isa<GlobalVariable>(V))
+ return true;
+
+ return false;
+}
OverflowResult llvm::computeOverflowForSignedAdd(const AddOperator *Add,
const DataLayout &DL,
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index aabedbd..524f931 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -446,6 +446,7 @@
Instruction *visitLandingPadInst(LandingPadInst &LI);
Instruction *visitVAStartInst(VAStartInst &I);
Instruction *visitVACopyInst(VACopyInst &I);
+ Instruction *visitFreeze(FreezeInst &I);
/// Specify what to return for unhandled instructions.
Instruction *visitInstruction(Instruction &I) { return nullptr; }
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index b1828d0..7656d66 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3131,6 +3131,15 @@
return nullptr;
}
+Instruction *InstCombiner::visitFreeze(FreezeInst &I) {
+ Value *Op0 = I.getOperand(0);
+
+ if (Value *V = SimplifyFreezeInst(Op0, SQ.getWithInstruction(&I)))
+ return replaceInstUsesWith(I, V);
+
+ return nullptr;
+}
+
/// Try to move the specified instruction from its current block into the
/// beginning of DestBlock, which can only happen if it's safe to move the
/// instruction past all of the instructions between it and the end of its