From 3285a6f426d02ee2d9ca880ac11838636a28c17d Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Thu, 10 Jun 2004 02:33:20 +0000
Subject: [PATCH] Fix a bug in my checkin from last night that caused
 miscompilations of 186.crafty, fhourstones and 132.ijpeg.

Bugpoint makes really nasty miscompilations embarassingly easy to find.  It
narrowed it down to the instcombiner and this testcase (from fhourstones):

bool %l7153_l4706_htstat_loopentry_2E_4_no_exit_2E_4(int* %i, [32 x int]* %works, int* %tmp.98.out) {
newFuncRoot:
        %tmp.96 = load int* %i          ; <int> [#uses=1]
        %tmp.97 = getelementptr [32 x int]* %works, long 0, int %tmp.96         ; <int*> [#uses=1]
        %tmp.98 = load int* %tmp.97             ; <int> [#uses=2]
        %tmp.99 = load int* %i          ; <int> [#uses=1]
        %tmp.100 = and int %tmp.99, 7           ; <int> [#uses=1]
        %tmp.101 = seteq int %tmp.100, 7                ; <bool> [#uses=2]
        %tmp.102 = cast bool %tmp.101 to int            ; <int> [#uses=0]
        br bool %tmp.101, label %codeRepl4.exitStub, label %codeRepl3.exitStub

codeRepl4.exitStub:             ; preds = %newFuncRoot
        store int %tmp.98, int* %tmp.98.out
        ret bool true

codeRepl3.exitStub:             ; preds = %newFuncRoot
        store int %tmp.98, int* %tmp.98.out
        ret bool false
}

... which only has one combination performed on it:

$ llvm-as < t.ll | opt -instcombine -debug | llvm-dis
IC: Old =       %tmp.101 = seteq int %tmp.100, 7                ; <bool> [#uses=1]
    New =       setne int %tmp.100, 0           ; <bool>:<badref> [#uses=0]
IC: MOD =       br bool %tmp.101, label %codeRepl3.exitStub, label %codeRepl4.exitStub
IC: MOD =       %tmp.97 = getelementptr [32 x int]* %works, uint 0, int %tmp.96         ; <int*> [#uses=1]

It doesn't get much better than this.  :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14109 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/InstructionCombining.cpp | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index e627392fb49..9d540b374a3 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -1582,14 +1582,10 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
               return ReplaceInstUsesWith(I, ConstantBool::get(isSetNE));
 
             // If we have ((X & C) == C), turn it into ((X & C) != 0).
-            if (CI == BOC) {
-              // Don't infinite loop if C is null and the & isn't folded yet.
-              if (CI->isNullValue())
-                return ReplaceInstUsesWith(I, ConstantBool::get(!isSetNE));
+            if (CI == BOC && isOneBitSet(CI))
               return new SetCondInst(isSetNE ? Instruction::SetEQ :
                                      Instruction::SetNE, Op0,
                                      Constant::getNullValue(CI->getType()));
-            }
 
             // Replace (and X, (1 << size(X)-1) != 0) with x < 0, converting X
             // to be a signed value as appropriate.