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MihailMihovMihailMihov
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[InstCombine] Add CTLZ -> CTTZ simplification (#164733)
This PR adds the simplification `ctlz(~x & (x - 1)) -> bitwidth - cttz(x, false)` ([Alive2](https://alive2.llvm.org/ce/z/vVDRCu)). Closes issue #164436
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‎llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp‎

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@@ -582,6 +582,18 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
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IC.Builder.CreateBinaryIntrinsic(Intrinsic::ctlz, C, Op1);
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return BinaryOperator::CreateSub(ConstCtlz, X);
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}
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// ctlz(~x & (x - 1)) -> bitwidth - cttz(x, false)
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if (Op0->hasOneUse() &&
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match(Op0,
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m_c_And(m_Not(m_Value(X)), m_Add(m_Deferred(X), m_AllOnes())))) {
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Type *Ty = II.getType();
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unsigned BitWidth = Ty->getScalarSizeInBits();
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auto *Cttz = IC.Builder.CreateIntrinsic(Intrinsic::cttz, Ty,
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{X, IC.Builder.getFalse()});
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auto *Bw = ConstantInt::get(Ty, APInt(BitWidth, BitWidth));
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return IC.replaceInstUsesWith(II, IC.Builder.CreateSub(Bw, Cttz));
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}
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}
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// cttz(Pow2) -> Log2(Pow2)

‎llvm/test/Transforms/InstCombine/ctlz-cttz.ll‎

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
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; RUN: opt < %s -S -passes=instcombine | FileCheck %s
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; ctpop(~i & (i - 1)) -> bitwidth - cttz(i, false)
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define i8 @ctlz_to_sub_bw_cttz(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[A0]], i1 false)
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; CHECK-NEXT: [[CLZ:%.*]] = sub nuw nsw i8 8, [[TMP1]]
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, -1
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%not = xor i8 %a0, -1
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%and = and i8 %dec, %not
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 false)
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ret i8 %clz
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}
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define i8 @ctlz_to_sub_bw_cttz_poison(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz_poison(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[A0]], i1 false)
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; CHECK-NEXT: [[CLZ:%.*]] = sub nuw nsw i8 8, [[TMP1]]
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, -1
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%not = xor i8 %a0, -1
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%and = and i8 %dec, %not
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 true)
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ret i8 %clz
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}
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define i8 @ctlz_to_sub_bw_cttz_different_add(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz_different_add(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[DEC:%.*]] = add i8 [[A0]], 1
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; CHECK-NEXT: [[NOT:%.*]] = xor i8 [[A0]], -1
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; CHECK-NEXT: [[AND:%.*]] = and i8 [[DEC]], [[NOT]]
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; CHECK-NEXT: [[CLZ:%.*]] = tail call range(i8 0, 9) i8 @llvm.ctlz.i8(i8 [[AND]], i1 false)
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, 1
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%not = xor i8 %a0, -1
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%and = and i8 %dec, %not
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 false)
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ret i8 %clz
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}
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define i8 @ctlz_to_sub_bw_cttz_different_xor(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz_different_xor(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[DEC:%.*]] = add i8 [[A0]], -1
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; CHECK-NEXT: [[NOT:%.*]] = xor i8 [[A0]], 1
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; CHECK-NEXT: [[AND:%.*]] = and i8 [[DEC]], [[NOT]]
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; CHECK-NEXT: [[CLZ:%.*]] = tail call range(i8 0, 9) i8 @llvm.ctlz.i8(i8 [[AND]], i1 false)
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, -1
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%not = xor i8 %a0, 1
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%and = and i8 %dec, %not
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 false)
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ret i8 %clz
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}
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declare void @use(i8)
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define i8 @ctlz_to_sub_bw_cttz_multi_use_dec(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz_multi_use_dec(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[DEC:%.*]] = add i8 [[A0]], -1
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; CHECK-NEXT: call void @use(i8 [[DEC]])
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; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[A0]], i1 false)
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; CHECK-NEXT: [[CLZ:%.*]] = sub nuw nsw i8 8, [[TMP1]]
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, -1
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call void @use(i8 %dec)
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%not = xor i8 %a0, -1
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%and = and i8 %dec, %not
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 false)
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ret i8 %clz
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}
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define i8 @ctlz_to_sub_bw_cttz_multi_use_not(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz_multi_use_not(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[NOT:%.*]] = xor i8 [[A0]], -1
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; CHECK-NEXT: call void @use(i8 [[NOT]])
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; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[A0]], i1 false)
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; CHECK-NEXT: [[CLZ:%.*]] = sub nuw nsw i8 8, [[TMP1]]
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, -1
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%not = xor i8 %a0, -1
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call void @use(i8 %not)
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%and = and i8 %dec, %not
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 false)
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ret i8 %clz
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}
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define i8 @ctlz_to_sub_bw_cttz_multi_use_and(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz_multi_use_and(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[DEC:%.*]] = add i8 [[A0]], -1
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; CHECK-NEXT: [[NOT:%.*]] = xor i8 [[A0]], -1
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; CHECK-NEXT: [[AND:%.*]] = and i8 [[DEC]], [[NOT]]
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; CHECK-NEXT: call void @use(i8 [[AND]])
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; CHECK-NEXT: [[CLZ:%.*]] = tail call range(i8 0, 9) i8 @llvm.ctlz.i8(i8 [[AND]], i1 false)
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, -1
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%not = xor i8 %a0, -1
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%and = and i8 %dec, %not
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call void @use(i8 %and)
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 false)
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ret i8 %clz
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}
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define i8 @ctlz_to_sub_bw_cttz_commute_and(i8 %a0) {
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; CHECK-LABEL: define i8 @ctlz_to_sub_bw_cttz_commute_and(
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; CHECK-SAME: i8 [[A0:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) i8 @llvm.cttz.i8(i8 [[A0]], i1 false)
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; CHECK-NEXT: [[CLZ:%.*]] = sub nuw nsw i8 8, [[TMP1]]
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; CHECK-NEXT: ret i8 [[CLZ]]
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;
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%dec = add i8 %a0, -1
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%not = xor i8 %a0, -1
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%and = and i8 %not, %dec
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%clz = tail call i8 @llvm.ctlz.i8(i8 %and, i1 false)
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ret i8 %clz
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}
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define <2 x i8> @ctlz_to_sub_bw_cttz_vec_splat(<2 x i8> %a0) {
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; CHECK-LABEL: define <2 x i8> @ctlz_to_sub_bw_cttz_vec_splat(
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; CHECK-SAME: <2 x i8> [[A0:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = call range(i8 0, 9) <2 x i8> @llvm.cttz.v2i8(<2 x i8> [[A0]], i1 false)
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; CHECK-NEXT: [[CLZ:%.*]] = sub nuw nsw <2 x i8> splat (i8 8), [[TMP1]]
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; CHECK-NEXT: ret <2 x i8> [[CLZ]]
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;
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%dec = add <2 x i8> %a0, <i8 -1, i8 -1>
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%not = xor <2 x i8> %a0, <i8 -1, i8 -1>
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%and = and <2 x i8> %dec, %not
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%clz = tail call <2 x i8>@llvm.ctlz.v2i8(<2 x i8> %and, i1 false)
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ret <2 x i8> %clz
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}

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