commit 48aefe15d08e4046b94715ea44e1f4a94af481a6
author Benjamin Kramer <benny.kra@googlemail.com> Tue May 25 22:53:43 2010 +0000
committer Benjamin Kramer <benny.kra@googlemail.com> Tue May 25 22:53:43 2010 +0000
tree d55724480716cf71ac68d3b169ed7a94119104d1
parent f10bc81b4e84003f8842e8ee7eee9d626de77e5f

Properly promote operands when optimizing a single-character memcmp.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104648 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SimplifyLibCalls.cpp

diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index b053cfc..0f3ab7d 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -558,9 +558,12 @@
     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());
     }