From 711b3402aafd607eeb9ec56395c78e98fe491e76 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 14 Nov 2004 07:33:16 +0000
Subject: [PATCH] Transform this:   %X = alloca ...   %Y = alloca ...     X ==
 Y

into false.  This allows us to simplify some stuff in eon (and probably
many other C++ programs) where operator= was checking for self assignment.
Folding this allows us to SROA several additional structs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17735 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/InstructionCombining.cpp | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 5af9aee165d..f1c1c3194b6 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -1870,12 +1870,14 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
   if (isa<UndefValue>(Op1))                  // X setcc undef -> undef
     return ReplaceInstUsesWith(I, UndefValue::get(Type::BoolTy));
 
-  // setcc <global/alloca*>, 0 - Global/Stack value addresses are never null!
-  if (isa<ConstantPointerNull>(Op1) && 
-      (isa<GlobalValue>(Op0) || isa<AllocaInst>(Op0)))
+  // setcc <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
+  // addresses never equal each other!  We already know that Op0 != Op1.
+  if ((isa<GlobalValue>(Op0) || isa<AllocaInst>(Op0) || 
+       isa<ConstantPointerNull>(Op0)) && 
+      (isa<GlobalValue>(Op1) || isa<AllocaInst>(Op1) || 
+       isa<ConstantPointerNull>(Op1)))
     return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
 
-
   // setcc's with boolean values can always be turned into bitwise operations
   if (Ty == Type::BoolTy) {
     switch (I.getOpcode()) {