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Properly promote operands when optimizing a single-character memcmp. 

llvm-svn: 104648
This commit is contained in:
Benjamin Kramer 2010-05-25 22:53:43 +00:00
parent 388f638511
commit 9439084cea
2 changed files with 19 additions and 4 deletions
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9
llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
View File

@ -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());
}

14
llvm/test/Transforms/SimplifyLibCalls/memcmp.ll
View File

@ -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
}