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[SLC] Transform strncpy(dst, "text", C) to memcpy(dst, "text\0\0\0", C) for C <= 128 only 

Transformation creates big strings for big C values, so bail out for C > 128.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D86004
This commit is contained in:
Dávid Bolvanský 2020-08-15 01:49:02 +02:00
parent 05e3ab41e4
commit f62de7c9c7
2 changed files with 27 additions and 5 deletions
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4
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -610,12 +610,16 @@ Value *LibCallSimplifier::optimizeStrNCpy(CallInst *CI, IRBuilderBase &B) {
// strncpy(a, "a", 4) - > memcpy(a, "a\0\0\0", 4)
if (Len > SrcLen + 1) {
if (Len <= 128) {
StringRef Str;
if (!getConstantStringInfo(Src, Str))
return nullptr;
std::string SrcStr = Str.str();
SrcStr.resize(Len, '\0');
Src = B.CreateGlobalString(SrcStr, "str");
} else {
return nullptr;
}
}
Type *PT = Callee->getFunctionType()->getParamType(0);

18
llvm/test/Transforms/InstCombine/strncpy-3.ll
View File

@ -38,3 +38,21 @@ define void @fill_with_zeros3(i8* %dst) {
tail call i8* @strncpy(i8* %dst, i8* getelementptr inbounds ([4 x i8], [4 x i8]* @str3, i64 0, i64 0), i64 4)
ret void
}
define void @fill_with_zeros4(i8* %dst) {
; CHECK-LABEL: @fill_with_zeros4(
; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(128) [[DST:%.*]], i8* nonnull align 1 dereferenceable(128) getelementptr inbounds ([129 x i8], [129 x i8]* @str.2, i64 0, i64 0), i64 128, i1 false)
; CHECK-NEXT: ret void
;
tail call i8* @strncpy(i8* %dst, i8* getelementptr inbounds ([4 x i8], [4 x i8]* @str3, i64 0, i64 0), i64 128)
ret void
}
define void @no_simplify(i8* %dst) {
; CHECK-LABEL: @no_simplify(
; CHECK-NEXT: [[TMP1:%.*]] = tail call i8* @strncpy(i8* nonnull dereferenceable(1) [[DST:%.*]], i8* nonnull dereferenceable(5) getelementptr inbounds ([4 x i8], [4 x i8]* @str3, i64 0, i64 0), i64 129)
; CHECK-NEXT: ret void
;
tail call i8* @strncpy(i8* %dst, i8* getelementptr inbounds ([4 x i8], [4 x i8]* @str3, i64 0, i64 0), i64 129)
ret void
}