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part of PR4405: disable a contentious optimization for

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strcmp -> memcmp when the lengths of the strings are unknown.

Patch by Nick Lewycky!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73751 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-06-19 04:17:36 +00:00
parent 10382fb71d
commit 849832c0fb
2 changed files with 3 additions and 15 deletions
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8
lib/Transforms/Scalar/SimplifyLibCalls.cpp
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@ -709,12 +709,10 @@ struct VISIBILITY_HIDDEN StrCmpOpt : public LibCallOptimization {
// strcmp(P, "x") -> memcmp(P, "x", 2)
uint64_t Len1 = GetStringLength(Str1P);
uint64_t Len2 = GetStringLength(Str2P);
if (Len1 || Len2) {
// Choose the smallest Len excluding 0 which means 'unknown'.
if (!Len1 || (Len2 && Len2 < Len1))
Len1 = Len2;
if (Len1 && Len2) {
return EmitMemCmp(Str1P, Str2P,
ConstantInt::get(TD->getIntPtrType(), Len1), B);
ConstantInt::get(TD->getIntPtrType(),
std::min(Len1, Len2)), B);
}
return 0;

10
test/Transforms/SimplifyLibCalls/2008-12-20-StrcmpMemcmp.ll
View File

@ -1,10 +0,0 @@
; RUN: llvm-as < %s | opt -simplify-libcalls | llvm-dis | grep call.*memcmp
@.str = internal constant [2 x i8] c"x\00"
declare i32 @strcmp(i8* %dest, i8* %src)
define i32 @foo(i8* %x, i8* %y) {
%A = call i32 @strcmp(i8* %x, i8* getelementptr ([2 x i8]* @.str, i32 0, i32 0))
ret i32 %A
}