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

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index cc5acf5d010..b26c6294dce 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4221,6 +4221,20 @@ bool llvm::isOverflowIntrinsicNoWrap(const WithOverflowInst *WO,
   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,