[llvm] r196611 - Don't use isNullValue to evaluate ConstantExpr

[Duncan P. N. Exon Smith]

Author: dexonsmith
Date: Fri Dec  6 15:48:36 2013
New Revision: 196611

URL: http://llvm.org/viewvc/llvm-project?rev=196611&view=rev
Log:
Don't use isNullValue to evaluate ConstantExpr

ConstantExpr can evaluate to false even when isNullValue gives false.

Fixes PR18143.

Added:
    llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=196611&r1=196610&r2=196611&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Fri Dec  6 15:48:36 2013
@@ -699,7 +699,10 @@ Instruction *InstCombiner::FoldOpIntoPhi
       Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
       Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
       Value *InV = 0;
-      if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
+      // Beware of ConstantExpr:  it may eventually evaluate to getNullValue,
+      // even if currently isNullValue gives false.
+      Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i));
+      if (InC && !isa<ConstantExpr>(InC))
         InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
       else
         InV = Builder->CreateSelect(PN->getIncomingValue(i),

Added: llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll?rev=196611&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/phi-select-constexpr.ll Fri Dec  6 15:48:36 2013
@@ -0,0 +1,19 @@
+; RUN: opt < %s -S -instcombine | FileCheck %s
+ at A = extern_weak global i32, align 4
+ at B = extern_weak global i32, align 4
+
+define i32 @foo(i1 %which) {
+entry:
+  br i1 %which, label %final, label %delay
+
+delay:
+  br label %final
+
+; CHECK-LABEL: final:
+; CHECK: phi i32 [ 1, %entry ], [ select (i1 icmp eq (i32* @A, i32* @B), i32 2, i32 1), %delay ]
+final:
+  %use2 = phi i1 [ false, %entry ], [ icmp eq (i32* @A, i32* @B), %delay ]
+  %value = select i1 %use2, i32 2, i32 1
+  ret i32 %value
+}
+