From 9439084cea7452256832f137cc9eaf79a1c7e45b Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Tue, 25 May 2010 22:53:43 +0000
Subject: [PATCH] Properly promote operands when optimizing a single-character
 memcmp.

llvm-svn: 104648
---
 llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp |  9 ++++++---
 llvm/test/Transforms/SimplifyLibCalls/memcmp.ll | 14 +++++++++++++-
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index b053cfc3b46d..0f3ab7d8b536 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -558,9 +558,12 @@ struct MemCmpOpt : public LibCallOptimization {
     if (Len == 0) // memcmp(s1,s2,0) -> 0
       return Constant::getNullValue(CI->getType());
 
-    if (Len == 1) { // memcmp(S1,S2,1) -> *LHS - *RHS
-      Value *LHSV = B.CreateLoad(CastToCStr(LHS, B), "lhsv");
-      Value *RHSV = B.CreateLoad(CastToCStr(RHS, B), "rhsv");
+    // memcmp(S1,S2,1) -> *(unsigned char*)LHS - *(unsigned char*)RHS
+    if (Len == 1) {
+      Value *LHSV = B.CreateZExt(B.CreateLoad(CastToCStr(LHS, B), "lhsc"),
+                                 CI->getType(), "lhsv");
+      Value *RHSV = B.CreateZExt(B.CreateLoad(CastToCStr(RHS, B), "rhsc"),
+                                 CI->getType(), "rhsv");
       return B.CreateSExt(B.CreateSub(LHSV, RHSV, "chardiff"), CI->getType());
     }
 
diff --git a/llvm/test/Transforms/SimplifyLibCalls/memcmp.ll b/llvm/test/Transforms/SimplifyLibCalls/memcmp.ll
index 640d232a7f0c..ee99501bc0d8 100644
--- a/llvm/test/Transforms/SimplifyLibCalls/memcmp.ll
+++ b/llvm/test/Transforms/SimplifyLibCalls/memcmp.ll
@@ -1,5 +1,5 @@
 ; Test that the memcmpOptimizer works correctly
-; RUN: opt < %s -simplify-libcalls -S | not grep {call.*memcmp}
+; RUN: opt < %s -simplify-libcalls -S | FileCheck %s
 
 @h = constant [2 x i8] c"h\00"		; <[2 x i8]*> [#uses=0]
 @hel = constant [4 x i8] c"hel\00"		; <[4 x i8]*> [#uses=0]
@@ -9,14 +9,26 @@ declare i32 @memcmp(i8*, i8*, i32)
 
 define void @test(i8* %P, i8* %Q, i32 %N, i32* %IP, i1* %BP) {
 	%A = call i32 @memcmp( i8* %P, i8* %P, i32 %N )		; <i32> [#uses=1]
+; CHECK-NOT: call {{.*}} memcmp
+; CHECK: volatile store
 	volatile store i32 %A, i32* %IP
 	%B = call i32 @memcmp( i8* %P, i8* %Q, i32 0 )		; <i32> [#uses=1]
+; CHECK-NOT: call {{.*}} memcmp
+; CHECK: volatile store
 	volatile store i32 %B, i32* %IP
 	%C = call i32 @memcmp( i8* %P, i8* %Q, i32 1 )		; <i32> [#uses=1]
+; CHECK: load
+; CHECK: zext
+; CHECK: load
+; CHECK: zext
+; CHECK: sub
+; CHECK: volatile store
 	volatile store i32 %C, i32* %IP
         %F = call i32 @memcmp(i8* getelementptr ([4 x i8]* @hel, i32 0, i32 0),
                               i8* getelementptr ([8 x i8]* @hello_u, i32 0, i32 0),
                               i32 3)
+; CHECK-NOT: call {{.*}} memcmp
+; CHECK: volatile store
         volatile store i32 %F, i32* %IP
 	ret void
 }