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[InstCombine] cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true' (PR50172) 

Zext doesn't change the number of trailing zeros, so narrow cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true'.

Proofs:
https://alive2.llvm.org/ce/z/o2dnjY

Solves https://bugs.llvm.org/show_bug.cgi?id=50172

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D101582
This commit is contained in:
Dávid Bolvanský 2021-05-03 17:04:50 +02:00
parent aad3113417
commit 27b651ca47
2 changed files with 23 additions and 13 deletions
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10
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -424,6 +424,7 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
"Expected cttz or ctlz intrinsic");
bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
Value *Op0 = II.getArgOperand(0);
Value *Op1 = II.getArgOperand(1);
Value *X;
// ctlz(bitreverse(x)) -> cttz(x)
// cttz(bitreverse(x)) -> ctlz(x)
@ -438,6 +439,15 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
if (match(Op0, m_Neg(m_Value(X))))
return IC.replaceOperand(II, 0, X);
// Zext doesn't change the number of trailing zeros, so narrow:
// cttz(zext(x)) -> zext(cttz(x)) if the 'ZeroIsUndef' parameter is 'true'.
if (match(Op0, m_OneUse(m_ZExt(m_Value(X)))) && match(Op1, m_One())) {
auto *Cttz = IC.Builder.CreateBinaryIntrinsic(Intrinsic::cttz, X,
IC.Builder.getTrue());
auto *ZextCttz = IC.Builder.CreateZExt(Cttz, II.getType());
return IC.replaceInstUsesWith(II, ZextCttz);
}
// cttz(abs(x)) -> cttz(x)
// cttz(nabs(x)) -> cttz(x)
Value *Y;

26
llvm/test/Transforms/InstCombine/cttz.ll
View File

@ -7,9 +7,9 @@ declare void @use(i32)
define i32 @cttz_zext_zero_undef(i16 %x) {
; CHECK-LABEL: @cttz_zext_zero_undef(
; CHECK-NEXT: [[Z:%.*]] = zext i16 [[X:%.*]] to i32
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Z]], i1 true), !range [[RNG0:![0-9]+]]
; CHECK-NEXT: ret i32 [[TZ]]
; CHECK-NEXT: [[TMP1:%.*]] = call i16 @llvm.cttz.i16(i16 [[X:%.*]], i1 true), !range [[RNG0:![0-9]+]]
; CHECK-NEXT: [[TMP2:%.*]] = zext i16 [[TMP1]] to i32
; CHECK-NEXT: ret i32 [[TMP2]]
;
%z = zext i16 %x to i32
%tz = call i32 @llvm.cttz.i32(i32 %z, i1 true)
@ -19,7 +19,7 @@ define i32 @cttz_zext_zero_undef(i16 %x) {
define i32 @cttz_zext_zero_def(i16 %x) {
; CHECK-LABEL: @cttz_zext_zero_def(
; CHECK-NEXT: [[Z:%.*]] = zext i16 [[X:%.*]] to i32
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Z]], i1 false), !range [[RNG0]]
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Z]], i1 false), !range [[RNG1:![0-9]+]]
; CHECK-NEXT: ret i32 [[TZ]]
;
%z = zext i16 %x to i32
@ -31,7 +31,7 @@ define i32 @cttz_zext_zero_undef_extra_use(i16 %x) {
; CHECK-LABEL: @cttz_zext_zero_undef_extra_use(
; CHECK-NEXT: [[Z:%.*]] = zext i16 [[X:%.*]] to i32
; CHECK-NEXT: call void @use(i32 [[Z]])
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Z]], i1 true), !range [[RNG0]]
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Z]], i1 true), !range [[RNG1]]
; CHECK-NEXT: ret i32 [[TZ]]
;
%z = zext i16 %x to i32
@ -42,9 +42,9 @@ define i32 @cttz_zext_zero_undef_extra_use(i16 %x) {
define <2 x i64> @cttz_zext_zero_undef_vec(<2 x i32> %x) {
; CHECK-LABEL: @cttz_zext_zero_undef_vec(
; CHECK-NEXT: [[Z:%.*]] = zext <2 x i32> [[X:%.*]] to <2 x i64>
; CHECK-NEXT: [[TZ:%.*]] = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[Z]], i1 true)
; CHECK-NEXT: ret <2 x i64> [[TZ]]
; CHECK-NEXT: [[TMP1:%.*]] = call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[X:%.*]], i1 true)
; CHECK-NEXT: [[TMP2:%.*]] = zext <2 x i32> [[TMP1]] to <2 x i64>
; CHECK-NEXT: ret <2 x i64> [[TMP2]]
;
%z = zext <2 x i32> %x to <2 x i64>
%tz = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> %z, i1 true)
@ -65,7 +65,7 @@ define <2 x i64> @cttz_zext_zero_def_vec(<2 x i32> %x) {
define i32 @cttz_sext_zero_undef(i16 %x) {
; CHECK-LABEL: @cttz_sext_zero_undef(
; CHECK-NEXT: [[S:%.*]] = sext i16 [[X:%.*]] to i32
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 true), !range [[RNG0]]
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 true), !range [[RNG1]]
; CHECK-NEXT: ret i32 [[TZ]]
;
%s = sext i16 %x to i32
@ -76,7 +76,7 @@ define i32 @cttz_sext_zero_undef(i16 %x) {
define i32 @cttz_sext_zero_def(i16 %x) {
; CHECK-LABEL: @cttz_sext_zero_def(
; CHECK-NEXT: [[S:%.*]] = zext i16 [[X:%.*]] to i32
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 false), !range [[RNG0]]
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 false), !range [[RNG1]]
; CHECK-NEXT: ret i32 [[TZ]]
;
%s = zext i16 %x to i32
@ -84,11 +84,11 @@ define i32 @cttz_sext_zero_def(i16 %x) {
ret i32 %tz
}
define i32 @cttz_zext_sero_undef_extra_use(i16 %x) {
; CHECK-LABEL: @cttz_zext_sero_undef_extra_use(
define i32 @cttz_sext_zero_undef_extra_use(i16 %x) {
; CHECK-LABEL: @cttz_sext_zero_undef_extra_use(
; CHECK-NEXT: [[S:%.*]] = sext i16 [[X:%.*]] to i32
; CHECK-NEXT: call void @use(i32 [[S]])
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 true), !range [[RNG0]]
; CHECK-NEXT: [[TZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[S]], i1 true), !range [[RNG1]]
; CHECK-NEXT: ret i32 [[TZ]]
;
%s = sext i16 %x to i32