maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[SLC] Optimize strncpy(a, a, C) to memcpy(a, a000, C) 

Solves PR47154
This commit is contained in:
Dávid Bolvanský 2020-08-13 22:22:33 +02:00
parent 524f591a39
commit 5ef2287d36
2 changed files with 49 additions and 3 deletions
llvm
lib/Transforms/Utils
SimplifyLibCalls.cpp
test/Transforms/InstCombine
strncpy-3.ll

12
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -608,9 +608,15 @@ Value *LibCallSimplifier::optimizeStrNCpy(CallInst *CI, IRBuilderBase &B) {
return Dst;
}
// Let strncpy handle the zero padding
if (Len > SrcLen + 1)
return nullptr;
// strncpy(a, "a", 4) - > memcpy(a, "a\0\0\0", 4)
if (Len > SrcLen + 1) {
StringRef Str;
if (!getConstantStringInfo(Src, Str))
return nullptr;
std::string SrcStr = Str.str();
SrcStr.resize(Len, '\0');
Src = B.CreateGlobalString(SrcStr, "str");
}
Type *PT = Callee->getFunctionType()->getParamType(0);
// strncpy(x, s, c) -> memcpy(align 1 x, align 1 s, c) [s and c are constant]

40
llvm/test/Transforms/InstCombine/strncpy-3.ll Normal file
View File

@ -0,0 +1,40 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -instcombine -S | FileCheck %s
@str = constant [2 x i8] c"a\00"
@str2 = constant [3 x i8] c"abc"
@str3 = constant [4 x i8] c"abcd"
declare i8* @strncpy(i8*, i8*, i64)
define void @fill_with_zeros(i8* %dst) {
; CHECK-LABEL: @fill_with_zeros(
; CHECK-NEXT: [[TMP1:%.*]] = bitcast i8* [[DST:%.*]] to i32*
; CHECK-NEXT: store i32 97, i32* [[TMP1]], align 1
; CHECK-NEXT: ret void
;
tail call i8* @strncpy(i8* %dst, i8* getelementptr inbounds ([2 x i8], [2 x i8]* @str, i64 0, i64 0), i64 4)
ret void
}
define void @fill_with_zeros2(i8* %dst) {
; CHECK-LABEL: @fill_with_zeros2(
; CHECK-NEXT: [[TMP1:%.*]] = bitcast i8* [[DST:%.*]] to i32*
; CHECK-NEXT: store i32 6513249, i32* [[TMP1]], align 1
; CHECK-NEXT: ret void
;
tail call i8* @strncpy(i8* %dst, i8* getelementptr inbounds ([3 x i8], [3 x i8]* @str2, i64 0, i64 0), i64 4)
ret void
}
define void @fill_with_zeros3(i8* %dst) {
; CHECK-LABEL: @fill_with_zeros3(
; CHECK-NEXT: [[TMP1:%.*]] = bitcast i8* [[DST:%.*]] to i32*
; CHECK-NEXT: store i32 1684234849, i32* [[TMP1]], align 1
; 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)
ret void
}