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[InstCombine] Simplify cttz/ctlz + icmp eq/ne into mask check
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Checking whether a number has a certain number of trailing / leading
zeros means checking whether it is of the form XXXX1000 / 0001XXXX,
which can be done with an and+icmp.

Related to https://bugs.llvm.org/show_bug.cgi?id=28668. As a next
step, this can be extended to non-equality predicates.

Differential Revision: https://reviews.llvm.org/D55745

llvm-svn: 349530
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@nikic
nikic committed Dec 18, 2018
1 parent 59ee2c5 commit 20853a7
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Showing 3 changed files with 68 additions and 37 deletions.
25 changes: 22 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View file
Expand Up @@ -2765,6 +2765,7 @@ Instruction *InstCombiner::foldICmpIntrinsicWithConstant(ICmpInst &Cmp,

// Handle icmp {eq|ne} <intrinsic>, Constant.
Type *Ty = II->getType();
unsigned BitWidth = C.getBitWidth();
switch (II->getIntrinsicID()) {
case Intrinsic::bswap:
Worklist.Add(II);
Expand All @@ -2773,21 +2774,39 @@ Instruction *InstCombiner::foldICmpIntrinsicWithConstant(ICmpInst &Cmp,
return &Cmp;

case Intrinsic::ctlz:
case Intrinsic::cttz:
case Intrinsic::cttz: {
// ctz(A) == bitwidth(A) -> A == 0 and likewise for !=
if (C == C.getBitWidth()) {
if (C == BitWidth) {
Worklist.Add(II);
Cmp.setOperand(0, II->getArgOperand(0));
Cmp.setOperand(1, ConstantInt::getNullValue(Ty));
return &Cmp;
}

// ctz(A) == C -> A & Mask1 == Mask2, where Mask2 only has bit C set
// and Mask1 has bits 0..C+1 set. Similar for ctl, but for high bits.
// Limit to one use to ensure we don't increase instruction count.
unsigned Num = C.getLimitedValue(BitWidth);
if (Num != BitWidth && II->hasOneUse()) {
bool IsTrailing = II->getIntrinsicID() == Intrinsic::cttz;
APInt Mask1 = IsTrailing ? APInt::getLowBitsSet(BitWidth, Num + 1)
: APInt::getHighBitsSet(BitWidth, Num + 1);
APInt Mask2 = IsTrailing
? APInt::getOneBitSet(BitWidth, Num)
: APInt::getOneBitSet(BitWidth, BitWidth - Num - 1);
Cmp.setOperand(0, Builder.CreateAnd(II->getArgOperand(0), Mask1));
Cmp.setOperand(1, ConstantInt::get(Ty, Mask2));
Worklist.Add(II);
return &Cmp;
}
break;
}

case Intrinsic::ctpop: {
// popcount(A) == 0 -> A == 0 and likewise for !=
// popcount(A) == bitwidth(A) -> A == -1 and likewise for !=
bool IsZero = C.isNullValue();
if (IsZero || C == C.getBitWidth()) {
if (IsZero || C == BitWidth) {
Worklist.Add(II);
Cmp.setOperand(0, II->getArgOperand(0));
auto *NewOp =
Expand Down
68 changes: 44 additions & 24 deletions llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
View file
Expand Up @@ -54,8 +54,7 @@ define i1 @ctlz_eq_bitwidth_i32(i32 %x) {

define i1 @ctlz_eq_zero_i32(i32 %x) {
; CHECK-LABEL: @ctlz_eq_zero_i32(
; CHECK-NEXT: [[LZ:%.*]] = tail call i32 @llvm.ctlz.i32(i32 [[X:%.*]], i1 false), !range !0
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[LZ]], 0
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%lz = tail call i32 @llvm.ctlz.i32(i32 %x, i1 false)
Expand All @@ -65,8 +64,7 @@ define i1 @ctlz_eq_zero_i32(i32 %x) {

define <2 x i1> @ctlz_ne_zero_v2i32(<2 x i32> %a) {
; CHECK-LABEL: @ctlz_ne_zero_v2i32(
; CHECK-NEXT: [[X:%.*]] = tail call <2 x i32> @llvm.ctlz.v2i32(<2 x i32> [[A:%.*]], i1 false)
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[X]], zeroinitializer
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i32> [[A:%.*]], <i32 -1, i32 -1>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%x = tail call <2 x i32> @llvm.ctlz.v2i32(<2 x i32> %a, i1 false)
Expand All @@ -76,8 +74,7 @@ define <2 x i1> @ctlz_ne_zero_v2i32(<2 x i32> %a) {

define i1 @ctlz_eq_bw_minus_1_i32(i32 %x) {
; CHECK-LABEL: @ctlz_eq_bw_minus_1_i32(
; CHECK-NEXT: [[LZ:%.*]] = tail call i32 @llvm.ctlz.i32(i32 [[X:%.*]], i1 false), !range !0
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[LZ]], 31
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X:%.*]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%lz = tail call i32 @llvm.ctlz.i32(i32 %x, i1 false)
Expand All @@ -87,8 +84,7 @@ define i1 @ctlz_eq_bw_minus_1_i32(i32 %x) {

define <2 x i1> @ctlz_ne_bw_minus_1_v2i32(<2 x i32> %a) {
; CHECK-LABEL: @ctlz_ne_bw_minus_1_v2i32(
; CHECK-NEXT: [[X:%.*]] = tail call <2 x i32> @llvm.ctlz.v2i32(<2 x i32> [[A:%.*]], i1 false)
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[X]], <i32 31, i32 31>
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[A:%.*]], <i32 1, i32 1>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%x = tail call <2 x i32> @llvm.ctlz.v2i32(<2 x i32> %a, i1 false)
Expand All @@ -98,8 +94,8 @@ define <2 x i1> @ctlz_ne_bw_minus_1_v2i32(<2 x i32> %a) {

define i1 @ctlz_eq_other_i32(i32 %x) {
; CHECK-LABEL: @ctlz_eq_other_i32(
; CHECK-NEXT: [[LZ:%.*]] = tail call i32 @llvm.ctlz.i32(i32 [[X:%.*]], i1 false), !range !0
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[LZ]], 24
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], -128
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[TMP1]], 128
; CHECK-NEXT: ret i1 [[CMP]]
;
%lz = tail call i32 @llvm.ctlz.i32(i32 %x, i1 false)
Expand All @@ -109,15 +105,28 @@ define i1 @ctlz_eq_other_i32(i32 %x) {

define <2 x i1> @ctlz_ne_other_v2i32(<2 x i32> %a) {
; CHECK-LABEL: @ctlz_ne_other_v2i32(
; CHECK-NEXT: [[X:%.*]] = tail call <2 x i32> @llvm.ctlz.v2i32(<2 x i32> [[A:%.*]], i1 false)
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[X]], <i32 24, i32 24>
; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i32> [[A:%.*]], <i32 -128, i32 -128>
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[TMP1]], <i32 128, i32 128>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%x = tail call <2 x i32> @llvm.ctlz.v2i32(<2 x i32> %a, i1 false)
%cmp = icmp ne <2 x i32> %x, <i32 24, i32 24>
ret <2 x i1> %cmp
}

define i1 @ctlz_eq_other_i32_multiuse(i32 %x, i32* %p) {
; CHECK-LABEL: @ctlz_eq_other_i32_multiuse(
; CHECK-NEXT: [[LZ:%.*]] = tail call i32 @llvm.ctlz.i32(i32 [[X:%.*]], i1 false), !range !0
; CHECK-NEXT: store i32 [[LZ]], i32* [[P:%.*]], align 4
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[LZ]], 24
; CHECK-NEXT: ret i1 [[CMP]]
;
%lz = tail call i32 @llvm.ctlz.i32(i32 %x, i1 false)
store i32 %lz, i32* %p
%cmp = icmp eq i32 %lz, 24
ret i1 %cmp
}

define <2 x i1> @ctlz_ne_bitwidth_v2i32(<2 x i32> %a) {
; CHECK-LABEL: @ctlz_ne_bitwidth_v2i32(
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[A:%.*]], zeroinitializer
Expand Down Expand Up @@ -150,8 +159,8 @@ define <2 x i1> @cttz_eq_bitwidth_v2i32(<2 x i32> %a) {

define i1 @cttz_eq_zero_i33(i33 %x) {
; CHECK-LABEL: @cttz_eq_zero_i33(
; CHECK-NEXT: [[TZ:%.*]] = tail call i33 @llvm.cttz.i33(i33 [[X:%.*]], i1 false), !range !1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i33 [[TZ]], 0
; CHECK-NEXT: [[TMP1:%.*]] = and i33 [[X:%.*]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i33 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%tz = tail call i33 @llvm.cttz.i33(i33 %x, i1 false)
Expand All @@ -161,8 +170,8 @@ define i1 @cttz_eq_zero_i33(i33 %x) {

define <2 x i1> @cttz_ne_zero_v2i32(<2 x i32> %a) {
; CHECK-LABEL: @cttz_ne_zero_v2i32(
; CHECK-NEXT: [[X:%.*]] = tail call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[A:%.*]], i1 false)
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[X]], zeroinitializer
; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i32> [[A:%.*]], <i32 1, i32 1>
; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i32> [[TMP1]], zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%x = tail call <2 x i32> @llvm.cttz.v2i32(<2 x i32> %a, i1 false)
Expand All @@ -172,8 +181,7 @@ define <2 x i1> @cttz_ne_zero_v2i32(<2 x i32> %a) {

define i1 @cttz_eq_bw_minus_1_i33(i33 %x) {
; CHECK-LABEL: @cttz_eq_bw_minus_1_i33(
; CHECK-NEXT: [[TZ:%.*]] = tail call i33 @llvm.cttz.i33(i33 [[X:%.*]], i1 false), !range !1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i33 [[TZ]], 32
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i33 [[X:%.*]], -4294967296
; CHECK-NEXT: ret i1 [[CMP]]
;
%tz = tail call i33 @llvm.cttz.i33(i33 %x, i1 false)
Expand All @@ -183,8 +191,7 @@ define i1 @cttz_eq_bw_minus_1_i33(i33 %x) {

define <2 x i1> @cttz_ne_bw_minus_1_v2i32(<2 x i32> %a) {
; CHECK-LABEL: @cttz_ne_bw_minus_1_v2i32(
; CHECK-NEXT: [[X:%.*]] = tail call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[A:%.*]], i1 false)
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[X]], <i32 31, i32 31>
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[A:%.*]], <i32 -2147483648, i32 -2147483648>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%x = tail call <2 x i32> @llvm.cttz.v2i32(<2 x i32> %a, i1 false)
Expand All @@ -194,8 +201,8 @@ define <2 x i1> @cttz_ne_bw_minus_1_v2i32(<2 x i32> %a) {

define i1 @cttz_eq_other_i33(i33 %x) {
; CHECK-LABEL: @cttz_eq_other_i33(
; CHECK-NEXT: [[TZ:%.*]] = tail call i33 @llvm.cttz.i33(i33 [[X:%.*]], i1 false), !range !1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i33 [[TZ]], 4
; CHECK-NEXT: [[TMP1:%.*]] = and i33 [[X:%.*]], 31
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i33 [[TMP1]], 16
; CHECK-NEXT: ret i1 [[CMP]]
;
%tz = tail call i33 @llvm.cttz.i33(i33 %x, i1 false)
Expand All @@ -205,15 +212,28 @@ define i1 @cttz_eq_other_i33(i33 %x) {

define <2 x i1> @cttz_ne_other_v2i32(<2 x i32> %a) {
; CHECK-LABEL: @cttz_ne_other_v2i32(
; CHECK-NEXT: [[X:%.*]] = tail call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[A:%.*]], i1 false)
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[X]], <i32 4, i32 4>
; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i32> [[A:%.*]], <i32 31, i32 31>
; CHECK-NEXT: [[CMP:%.*]] = icmp ne <2 x i32> [[TMP1]], <i32 16, i32 16>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%x = tail call <2 x i32> @llvm.cttz.v2i32(<2 x i32> %a, i1 false)
%cmp = icmp ne <2 x i32> %x, <i32 4, i32 4>
ret <2 x i1> %cmp
}

define i1 @cttz_eq_other_i33_multiuse(i33 %x, i33* %p) {
; CHECK-LABEL: @cttz_eq_other_i33_multiuse(
; CHECK-NEXT: [[LZ:%.*]] = tail call i33 @llvm.cttz.i33(i33 [[X:%.*]], i1 false), !range !1
; CHECK-NEXT: store i33 [[LZ]], i33* [[P:%.*]], align 4
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i33 [[LZ]], 4
; CHECK-NEXT: ret i1 [[CMP]]
;
%lz = tail call i33 @llvm.cttz.i33(i33 %x, i1 false)
store i33 %lz, i33* %p
%cmp = icmp eq i33 %lz, 4
ret i1 %cmp
}

define i1 @ctpop_eq_zero_i11(i11 %x) {
; CHECK-LABEL: @ctpop_eq_zero_i11(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i11 [[X:%.*]], 0
Expand Down
12 changes: 2 additions & 10 deletions llvm/test/Transforms/InstCombine/intrinsics.ll
View file
Expand Up @@ -354,13 +354,9 @@ define i1 @cttz_knownbits3(i32 %arg) {
ret i1 %res
}

; TODO: The icmp is unnecessary given the known bits of the input.
define <2 x i1> @cttz_knownbits3_vec(<2 x i32> %arg) {
; CHECK-LABEL: @cttz_knownbits3_vec(
; CHECK-NEXT: [[OR:%.*]] = or <2 x i32> [[ARG:%.*]], <i32 4, i32 4>
; CHECK-NEXT: [[CNT:%.*]] = call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[OR]], i1 true)
; CHECK-NEXT: [[RES:%.*]] = icmp eq <2 x i32> [[CNT]], <i32 3, i32 3>
; CHECK-NEXT: ret <2 x i1> [[RES]]
; CHECK-NEXT: ret <2 x i1> zeroinitializer
;
%or = or <2 x i32> %arg, <i32 4, i32 4>
%cnt = call <2 x i32> @llvm.cttz.v2i32(<2 x i32> %or, i1 true) nounwind readnone
Expand Down Expand Up @@ -450,13 +446,9 @@ define i1 @ctlz_knownbits3(i8 %arg) {
ret i1 %res
}

; TODO: The icmp is unnecessary given the known bits of the input.
define <2 x i1> @ctlz_knownbits3_vec(<2 x i8> %arg) {
; CHECK-LABEL: @ctlz_knownbits3_vec(
; CHECK-NEXT: [[OR:%.*]] = or <2 x i8> [[ARG:%.*]], <i8 32, i8 32>
; CHECK-NEXT: [[CNT:%.*]] = call <2 x i8> @llvm.ctlz.v2i8(<2 x i8> [[OR]], i1 true)
; CHECK-NEXT: [[RES:%.*]] = icmp eq <2 x i8> [[CNT]], <i8 3, i8 3>
; CHECK-NEXT: ret <2 x i1> [[RES]]
; CHECK-NEXT: ret <2 x i1> zeroinitializer
;
%or = or <2 x i8> %arg, <i8 32, i8 32>
%cnt = call <2 x i8> @llvm.ctlz.v2i8(<2 x i8> %or, i1 true) nounwind readnone
Expand Down

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