From 42883d0ac4388c12c856225760fe591a361db7bc Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Fri, 6 Dec 2013 21:48:36 +0000
Subject: [PATCH] Don't use isNullValue to evaluate ConstantExpr

ConstantExpr can evaluate to false even when isNullValue gives false.

Fixes PR18143.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196611 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstructionCombining.cpp      |  5 ++++-
 .../InstCombine/phi-select-constexpr.ll       | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/InstCombine/phi-select-constexpr.ll

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 27f1a3eb699..191a101e0a3 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -699,7 +699,10 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
       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),
diff --git a/test/Transforms/InstCombine/phi-select-constexpr.ll b/test/Transforms/InstCombine/phi-select-constexpr.ll
new file mode 100644
index 00000000000..054e0691d47
--- /dev/null
+++ b/test/Transforms/InstCombine/phi-select-constexpr.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -S -instcombine | FileCheck %s
+@A = extern_weak global i32, align 4
+@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
+}
+