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[SimplifyLibCalls] Fold memchr() with size 1 

If the memchr() size is 1, then we can convert the call into a
single-byte comparison. This works even if both the string and the
character are unknown.

Split off from https://reviews.llvm.org/D122836.
This commit is contained in:
Martin Sebor 2022-04-04 10:36:57 +02:00 committed by Nikita Popov
parent 0f08875744
commit d18991debf
3 changed files with 26 additions and 9 deletions
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16
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -884,13 +884,25 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilderBase &B) {
Value *SrcStr = CI->getArgOperand(0);
Value *Size = CI->getArgOperand(2);
annotateNonNullAndDereferenceable(CI, 0, Size, DL);
ConstantInt *CharC = dyn_cast<ConstantInt>(CI->getArgOperand(1));
Value *CharVal = CI->getArgOperand(1);
ConstantInt *CharC = dyn_cast<ConstantInt>(CharVal);
ConstantInt *LenC = dyn_cast<ConstantInt>(Size);
// memchr(x, y, 0) -> null
if (LenC) {
if (LenC->isZero())
return Constant::getNullValue(CI->getType());
if (LenC->isOne()) {
// Fold memchr(x, y, 1) --> *x == y ? x : null for any x and y,
// constant or otherwise.
Value *Val = B.CreateLoad(B.getInt8Ty(), SrcStr, "memchr.char0");
// Slice off the character's high end bits.
CharVal = B.CreateTrunc(CharVal, B.getInt8Ty());
Value *Cmp = B.CreateICmpEQ(Val, CharVal, "memchr.char0cmp");
Value *NullPtr = Constant::getNullValue(CI->getType());
return B.CreateSelect(Cmp, SrcStr, NullPtr, "memchr.sel");
}
} else {
// From now on we need at least constant length and string.
return nullptr;
@ -939,7 +951,7 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilderBase &B) {
Value *BitfieldC = B.getInt(Bitfield);
// Adjust width of "C" to the bitfield width, then mask off the high bits.
Value *C = B.CreateZExtOrTrunc(CI->getArgOperand(1), BitfieldC->getType());
Value *C = B.CreateZExtOrTrunc(CharVal, BitfieldC->getType());
C = B.CreateAnd(C, B.getIntN(Width, 0xFF));
// First check that the bit field access is within bounds.

13
llvm/test/Transforms/InstCombine/memchr-3.ll
View File

@ -41,8 +41,10 @@ define i8* @fold_memchr_a12345_2_1() {
define i8* @fold_memchr_ax_257_1(i32 %chr, i64 %n) {
; CHECK-LABEL: @fold_memchr_ax_257_1(
; CHECK-NEXT: [[RES:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([0 x i8], [0 x i8]* @ax, i64 0, i64 0), i32 257, i64 1)
; CHECK-NEXT: ret i8* [[RES]]
; CHECK-NEXT: [[MEMCHR_CHAR0:%.*]] = load i8, i8* getelementptr inbounds ([0 x i8], [0 x i8]* @ax, i64 0, i64 0), align 1
; CHECK-NEXT: [[MEMCHR_CHAR0CMP:%.*]] = icmp eq i8 [[MEMCHR_CHAR0]], 1
; CHECK-NEXT: [[MEMCHR_SEL:%.*]] = select i1 [[MEMCHR_CHAR0CMP]], i8* getelementptr inbounds ([0 x i8], [0 x i8]* @ax, i64 0, i64 0), i8* null
; CHECK-NEXT: ret i8* [[MEMCHR_SEL]]
;
%ptr = getelementptr [0 x i8], [0 x i8]* @ax, i32 0, i32 0
@ -55,8 +57,11 @@ define i8* @fold_memchr_ax_257_1(i32 %chr, i64 %n) {
define i8* @fold_memchr_ax_c_1(i32 %chr, i64 %n) {
; CHECK-LABEL: @fold_memchr_ax_c_1(
; CHECK-NEXT: [[RES:%.*]] = call i8* @memchr(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([0 x i8], [0 x i8]* @ax, i64 0, i64 0), i32 [[CHR:%.*]], i64 1)
; CHECK-NEXT: ret i8* [[RES]]
; CHECK-NEXT: [[MEMCHR_CHAR0:%.*]] = load i8, i8* getelementptr inbounds ([0 x i8], [0 x i8]* @ax, i64 0, i64 0), align 1
; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[CHR:%.*]] to i8
; CHECK-NEXT: [[MEMCHR_CHAR0CMP:%.*]] = icmp eq i8 [[MEMCHR_CHAR0]], [[TMP1]]
; CHECK-NEXT: [[MEMCHR_SEL:%.*]] = select i1 [[MEMCHR_CHAR0CMP]], i8* getelementptr inbounds ([0 x i8], [0 x i8]* @ax, i64 0, i64 0), i8* null
; CHECK-NEXT: ret i8* [[MEMCHR_SEL]]
;
%ptr = getelementptr [0 x i8], [0 x i8]* @ax, i32 0, i32 0

6
llvm/test/Transforms/InstCombine/memchr.ll
View File

@ -174,9 +174,9 @@ define i1 @test13(i32 %C) {
define i1 @test14(i32 %C) {
; CHECK-LABEL: @test14(
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[C:%.*]], 255
; CHECK-NEXT: [[MEMCHR_BITS:%.*]] = icmp eq i32 [[TMP1]], 31
; CHECK-NEXT: ret i1 [[MEMCHR_BITS]]
; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[C:%.*]] to i8
; CHECK-NEXT: [[MEMCHR_CHAR0CMP:%.*]] = icmp eq i8 [[TMP1]], 31
; CHECK-NEXT: ret i1 [[MEMCHR_CHAR0CMP]]
;
%dst = call i8* @memchr(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @single, i64 0, i64 0), i32 %C, i32 1)
%cmp = icmp ne i8* %dst, null