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simplify-libcalls: fold strncmp(x, y, 1) -> memcmp(x, y, 1)

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The memcmp will be optimized further and even the pathological case
'strstr(x, "x") == x' generates optimal code now.

llvm-svn: 106097
This commit is contained in:
Benjamin Kramer 2010-06-16 10:30:29 +00:00
parent 46b89e05fd
commit f600dc2eed
2 changed files with 10 additions and 0 deletions
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3
lib/Transforms/Scalar/SimplifyLibCalls.cpp
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@ -342,6 +342,9 @@ struct StrNCmpOpt : public LibCallOptimization {
if (Length == 0) // strncmp(x,y,0) -> 0
return ConstantInt::get(CI->getType(), 0);
if (TD && Length == 1) // strncmp(x,y,1) -> memcmp(x,y,1)
return EmitMemCmp(Str1P, Str2P, CI->getOperand(3), B, TD);
std::string Str1, Str2;
bool HasStr1 = GetConstantStringInfo(Str1P, Str1);
bool HasStr2 = GetConstantStringInfo(Str2P, Str2);

7
test/Transforms/SimplifyLibCalls/StrNCmp.ll
View File

@ -2,6 +2,9 @@
; RUN: opt < %s -simplify-libcalls -S | \
; RUN: not grep {call.*strncmp}
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32"
target triple = "i386-apple-darwin9.0"
@hello = constant [6 x i8] c"hello\00" ; <[6 x i8]*> [#uses=1]
@hell = constant [5 x i8] c"hell\00" ; <[5 x i8]*> [#uses=1]
@null = constant [1 x i8] zeroinitializer ; <[1 x i8]*> [#uses=1]
@ -26,3 +29,7 @@ define i32 @main() {
ret i32 %rslt4
}
define i32 @test1(i8* %P, i8* %Q) {
%cmp = call i32 @strncmp(i8* %P, i8* %Q, i32 1)
ret i32 %cmp
}