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Teach SimplifyLibCalls to fold memcmp calls with constant arguments. 

llvm-svn: 86141
This commit is contained in:
Benjamin Kramer 2009-11-05 17:44:22 +00:00
parent 65ae200a13
commit b971445ab7
2 changed files with 15 additions and 4 deletions
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15
llvm/lib/Transforms/Scalar/SimplifyLibCalls.cpp
View File

@ -955,6 +955,17 @@ struct MemCmpOpt : public LibCallOptimization {
return B.CreateZExt(B.CreateXor(LHSV, RHSV, "shortdiff"), CI->getType());
}
// Constant folding: memcmp(x, y, l) -> cnst (all arguments are constant)
std::string LHSStr, RHSStr;
if (GetConstantStringInfo(LHS, LHSStr) &&
GetConstantStringInfo(RHS, RHSStr)) {
// Make sure we're not reading out-of-bounds memory.
if (Len > LHSStr.length() || Len > RHSStr.length())
return 0;
uint64_t Ret = memcmp(LHSStr.data(), RHSStr.data(), Len);
return ConstantInt::get(CI->getType(), Ret);
}
return 0;
}
};
@ -2479,10 +2490,6 @@ bool SimplifyLibCalls::doInitialization(Module &M) {
// lround, lroundf, lroundl:
// * lround(cnst) -> cnst'
//
// memcmp:
// * memcmp(x,y,l) -> cnst
// (if all arguments are constant and strlen(x) <= l and strlen(y) <= l)
//
// pow, powf, powl:
// * pow(exp(x),y) -> exp(x*y)
// * pow(sqrt(x),y) -> pow(x,y*0.5)

4
llvm/test/Transforms/SimplifyLibCalls/memcmp.ll
View File

@ -17,6 +17,10 @@ define void @test(i8* %P, i8* %Q, i32 %N, i32* %IP, i1* %BP) {
%D = call i32 @memcmp( i8* %P, i8* %Q, i32 2 ) ; <i32> [#uses=1]
%E = icmp eq i32 %D, 0 ; <i1> [#uses=1]
volatile store i1 %E, i1* %BP
%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)
volatile store i32 %F, i32* %IP
ret void
}