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Differential D86004

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

Authored by xbolva00 on Aug 14 2020, 4:10 PM.

Details

Reviewers
efriedma
Commits
rGf62de7c9c711: [SLC] Transform strncpy(dst, "text", C) to memcpy(dst, "text\0\0\0", C) for C…
Summary

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

Diff Detail

Event Timeline

xbolva00 created this revision.Aug 14 2020, 4:10 PM
Herald added a project: Restricted Project. · View Herald TranscriptAug 14 2020, 4:10 PM
Herald added subscribers: llvm-commits, hiraditya. · View Herald Transcript
xbolva00 requested review of this revision.Aug 14 2020, 4:10 PM
efriedma accepted this revision.Aug 14 2020, 4:28 PM

LGTM, thanks

This revision is now accepted and ready to land.Aug 14 2020, 4:28 PM
Harbormaster completed remote builds in B68487: Diff 285781.Aug 14 2020, 4:45 PM
Closed by commit rGf62de7c9c711: [SLC] Transform strncpy(dst, "text", C) to memcpy(dst, "text\0\0\0", C) for C… (authored by xbolva00). · Explain WhyAug 14 2020, 4:53 PM
This revision was automatically updated to reflect the committed changes.
xbolva00 added a commit: rGf62de7c9c711: [SLC] Transform strncpy(dst, "text", C) to memcpy(dst, "text\0\0\0", C) for C….

Revision Contents

PathSize
llvm/
lib/
Transforms/
Utils/
14 lines
test/
Transforms/
InstCombine/
18 lines

Diff 285792

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

Show First 20 Lines • Show All 604 Lines • ▼ Show 20 Lines if (SrcLen == 0) {
AttrBuilder ArgAttrs(CI->getAttributes().getParamAttributes(0)); AttrBuilder ArgAttrs(CI->getAttributes().getParamAttributes(0));
NewCI->setAttributes(NewCI->getAttributes().addParamAttributes( NewCI->setAttributes(NewCI->getAttributes().addParamAttributes(
CI->getContext(), 0, ArgAttrs)); CI->getContext(), 0, ArgAttrs));
return Dst; return Dst;
} }
// strncpy(a, "a", 4) - > memcpy(a, "a\0\0\0", 4) // strncpy(a, "a", 4) - > memcpy(a, "a\0\0\0", 4)
if (Len > SrcLen + 1) { if (Len > SrcLen + 1) {
if (Len <= 128) {
StringRef Str; StringRef Str;
if (!getConstantStringInfo(Src, Str)) if (!getConstantStringInfo(Src, Str))
return nullptr; return nullptr;
std::string SrcStr = Str.str(); std::string SrcStr = Str.str();
SrcStr.resize(Len, '\0'); SrcStr.resize(Len, '\0');
Src = B.CreateGlobalString(SrcStr, "str"); Src = B.CreateGlobalString(SrcStr, "str");
} else {
return nullptr;
}
} }
Type *PT = Callee->getFunctionType()->getParamType(0); Type *PT = Callee->getFunctionType()->getParamType(0);
// strncpy(x, s, c) -> memcpy(align 1 x, align 1 s, c) [s and c are constant] // strncpy(x, s, c) -> memcpy(align 1 x, align 1 s, c) [s and c are constant]
CallInst *NewCI = B.CreateMemCpy(Dst, Align(1), Src, Align(1), CallInst *NewCI = B.CreateMemCpy(Dst, Align(1), Src, Align(1),
ConstantInt::get(DL.getIntPtrType(PT), Len)); ConstantInt::get(DL.getIntPtrType(PT), Len));
NewCI->setAttributes(CI->getAttributes()); NewCI->setAttributes(CI->getAttributes());
return Dst; return Dst;
▲ Show 20 Lines • Show All 2,883 Lines • Show Last 20 Lines

llvm/test/Transforms/InstCombine/strncpy-3.ll

Show All 32 Lines
; CHECK-LABEL: @fill_with_zeros3( ; CHECK-LABEL: @fill_with_zeros3(
; CHECK-NEXT: [[TMP1:%.*]] = bitcast i8* [[DST:%.*]] to i32* ; CHECK-NEXT: [[TMP1:%.*]] = bitcast i8* [[DST:%.*]] to i32*
; CHECK-NEXT: store i32 1684234849, i32* [[TMP1]], align 1 ; CHECK-NEXT: store i32 1684234849, i32* [[TMP1]], align 1
; CHECK-NEXT: ret void ; 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 4) tail call i8* @strncpy(i8* %dst, i8* getelementptr inbounds ([4 x i8], [4 x i8]* @str3, i64 0, i64 0), i64 4)
ret void 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
}