From ad000d8f16b5ca8ff2460dd60d657bfa55425855 Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Thu, 13 Jan 2011 10:43:08 +0000
Subject: [PATCH] Remove some wrong code which fortunately was never executed
 (as explained in the comment I added): an extern weak global may have a null
 address.

llvm-svn: 123373
---
 llvm/lib/Analysis/InstructionSimplify.cpp | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index b3a3acab6148..d4b89cebd598 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1024,12 +1024,15 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
-  // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
-  // addresses never equal each other!  We already know that Op0 != Op1.
-  if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
-       isa<ConstantPointerNull>(LHS)) &&
-      (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
-       isa<ConstantPointerNull>(RHS)))
+  // icmp <alloca*>, <global/alloca*/null> - Different stack variables have
+  // different addresses, and what's more the address of a stack variable is
+  // never null or equal to the address of a global.  Note that generalizing
+  // to the case where LHS is a global variable address or null is pointless,
+  // since if both LHS and RHS are constants then we already constant folded
+  // the compare, and if only one of them is then we moved it to RHS already.
+  if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
+                               isa<ConstantPointerNull>(RHS)))
+    // We already know that LHS != LHS.
     return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
 
   // If the comparison is with the result of a select instruction, check whether