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[InstCombine] Handle IsInf/IsZero idioms (#80607)
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This patch does the following folds:
```
icmp eq/ne (bitcast X to int), (bitcast +/-inf to int) -> llvm.is.fpclass(X, (~)fcPosInf/fcNegInf)
icmp eq/ne (bitcast X to int), (bitcast +0/-0 to int) -> llvm.is.fpclass(X, (~)fcPosZero/fcNegZero)
```
Alive2: https://alive2.llvm.org/ce/z/JJmEE9
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@dtcxzyw
dtcxzyw committed Feb 8, 2024
1 parent 8f6e13e commit c8ca98a
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Showing 2 changed files with 169 additions and 11 deletions.
30 changes: 22 additions & 8 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3229,16 +3229,16 @@ Instruction *InstCombinerImpl::foldICmpBitCast(ICmpInst &Cmp) {
if (Cmp.isEquality() && match(Op1, m_Zero()))
return new ICmpInst(Pred, X, ConstantInt::getNullValue(X->getType()));

// If this is a sign-bit test of a bitcast of a casted FP value, eliminate
// the FP extend/truncate because that cast does not change the sign-bit.
// This is true for all standard IEEE-754 types and the X86 80-bit type.
// The sign-bit is always the most significant bit in those types.
const APInt *C;
bool TrueIfSigned;
if (match(Op1, m_APInt(C)) && Bitcast->hasOneUse() &&
isSignBitCheck(Pred, *C, TrueIfSigned)) {
if (match(BCSrcOp, m_FPExt(m_Value(X))) ||
match(BCSrcOp, m_FPTrunc(m_Value(X)))) {
if (match(Op1, m_APInt(C)) && Bitcast->hasOneUse()) {
// If this is a sign-bit test of a bitcast of a casted FP value, eliminate
// the FP extend/truncate because that cast does not change the sign-bit.
// This is true for all standard IEEE-754 types and the X86 80-bit type.
// The sign-bit is always the most significant bit in those types.
if (isSignBitCheck(Pred, *C, TrueIfSigned) &&
(match(BCSrcOp, m_FPExt(m_Value(X))) ||
match(BCSrcOp, m_FPTrunc(m_Value(X))))) {
// (bitcast (fpext/fptrunc X)) to iX) < 0 --> (bitcast X to iY) < 0
// (bitcast (fpext/fptrunc X)) to iX) > -1 --> (bitcast X to iY) > -1
Type *XType = X->getType();
Expand All @@ -3257,6 +3257,20 @@ Instruction *InstCombinerImpl::foldICmpBitCast(ICmpInst &Cmp) {
ConstantInt::getAllOnesValue(NewType));
}
}

// icmp eq/ne (bitcast X to int), special fp -> llvm.is.fpclass(X, class)
Type *FPType = SrcType->getScalarType();
if (!Cmp.getParent()->getParent()->hasFnAttribute(
Attribute::NoImplicitFloat) &&
Cmp.isEquality() && FPType->isIEEELikeFPTy()) {
FPClassTest Mask = APFloat(FPType->getFltSemantics(), *C).classify();
if (Mask & (fcInf | fcZero)) {
if (Pred == ICmpInst::ICMP_NE)
Mask = ~Mask;
return replaceInstUsesWith(Cmp,
Builder.createIsFPClass(BCSrcOp, Mask));
}
}
}
}

Expand Down
150 changes: 147 additions & 3 deletions llvm/test/Transforms/InstCombine/fpclass-check-idioms.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -40,13 +40,11 @@ define i1 @f64_fcnan_fcinf(double %a) {
ret i1 %cmp
}

; TODO: handle more fpclass check idioms
define i1 @f32_fcinf(float %a) {
; CHECK-LABEL: define i1 @f32_fcinf(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[A]])
; CHECK-NEXT: [[AND:%.*]] = bitcast float [[TMP1]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[AND]], 2139095040
; CHECK-NEXT: [[CMP:%.*]] = fcmp oeq float [[TMP1]], 0x7FF0000000000000
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
Expand All @@ -55,6 +53,63 @@ define i1 @f32_fcinf(float %a) {
ret i1 %cmp
}

define i1 @f32_fcposinf(float %a) {
; CHECK-LABEL: define i1 @f32_fcposinf(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = fcmp oeq float [[A]], 0x7FF0000000000000
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%cmp = icmp eq i32 %i32, 2139095040
ret i1 %cmp
}

define i1 @f32_fcneginf(float %a) {
; CHECK-LABEL: define i1 @f32_fcneginf(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = fcmp oeq float [[A]], 0xFFF0000000000000
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%cmp = icmp eq i32 %i32, 4286578688
ret i1 %cmp
}

define i1 @f32_fcposzero(float %a) {
; CHECK-LABEL: define i1 @f32_fcposzero(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = call i1 @llvm.is.fpclass.f32(float [[A]], i32 64)
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%cmp = icmp eq i32 %i32, 0
ret i1 %cmp
}

define i1 @f32_fcnegzero(float %a) {
; CHECK-LABEL: define i1 @f32_fcnegzero(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = call i1 @llvm.is.fpclass.f32(float [[A]], i32 32)
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%cmp = icmp eq i32 %i32, 2147483648
ret i1 %cmp
}

define i1 @f32_fczero(float %a) {
; CHECK-LABEL: define i1 @f32_fczero(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = fcmp oeq float [[A]], 0.000000e+00
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%and = and i32 %i32, 2147483647
%cmp = icmp eq i32 %and, 0
ret i1 %cmp
}

; TODO: handle more fpclass check idioms
define i1 @f32_fcnan(float %a) {
; CHECK-LABEL: define i1 @f32_fcnan(
; CHECK-SAME: float [[A:%.*]]) {
Expand Down Expand Up @@ -101,6 +156,19 @@ define <2 x i1> @f32_fcnan_fcinf_vec(<2 x float> %a) {
ret <2 x i1> %cmp
}

define <2 x i1> @f32_fcinf_vec(<2 x float> %a) {
; CHECK-LABEL: define <2 x i1> @f32_fcinf_vec(
; CHECK-SAME: <2 x float> [[A:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call <2 x float> @llvm.fabs.v2f32(<2 x float> [[A]])
; CHECK-NEXT: [[CMP:%.*]] = fcmp oeq <2 x float> [[TMP1]], <float 0x7FF0000000000000, float 0x7FF0000000000000>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%i32 = bitcast <2 x float> %a to <2 x i32>
%and = and <2 x i32> %i32, <i32 2147483647, i32 2147483647>
%cmp = icmp eq <2 x i32> %and, <i32 2139095040, i32 2139095040>
ret <2 x i1> %cmp
}

; Negative tests

define i1 @f32_fcnan_fcinf_wrong_mask1(float %a) {
Expand Down Expand Up @@ -158,6 +226,18 @@ define i1 @f32_fcnan_fcinf_wrong_pred(float %a) {
ret i1 %cmp
}

define i1 @f32_fcposzero_wrong_pred(float %a) {
; CHECK-LABEL: define i1 @f32_fcposzero_wrong_pred(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[I32:%.*]] = bitcast float [[A]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[I32]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%cmp = icmp slt i32 %i32, 0
ret i1 %cmp
}

define i1 @f32_fcnan_fcinf_wrong_type1(<2 x float> %a) {
; CHECK-LABEL: define i1 @f32_fcnan_fcinf_wrong_type1(
; CHECK-SAME: <2 x float> [[A:%.*]]) {
Expand All @@ -172,6 +252,18 @@ define i1 @f32_fcnan_fcinf_wrong_type1(<2 x float> %a) {
ret i1 %cmp
}

define i1 @f32_fcposinf_wrong_type1(<2 x float> %a) {
; CHECK-LABEL: define i1 @f32_fcposinf_wrong_type1(
; CHECK-SAME: <2 x float> [[A:%.*]]) {
; CHECK-NEXT: [[I64:%.*]] = bitcast <2 x float> [[A]] to i64
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[I64]], 2139095040
; CHECK-NEXT: ret i1 [[CMP]]
;
%i64 = bitcast <2 x float> %a to i64
%cmp = icmp eq i64 %i64, 2139095040
ret i1 %cmp
}

define i1 @f32_fcnan_fcinf_wrong_type2(x86_fp80 %a) {
; CHECK-LABEL: define i1 @f32_fcnan_fcinf_wrong_type2(
; CHECK-SAME: x86_fp80 [[A:%.*]]) {
Expand All @@ -186,6 +278,18 @@ define i1 @f32_fcnan_fcinf_wrong_type2(x86_fp80 %a) {
ret i1 %cmp
}

define i1 @f32_fcposzero_wrong_type2(x86_fp80 %a) {
; CHECK-LABEL: define i1 @f32_fcposzero_wrong_type2(
; CHECK-SAME: x86_fp80 [[A:%.*]]) {
; CHECK-NEXT: [[I80:%.*]] = bitcast x86_fp80 [[A]] to i80
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i80 [[I80]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%i80 = bitcast x86_fp80 %a to i80
%cmp = icmp eq i80 %i80, 0
ret i1 %cmp
}

define i1 @f32_fcnan_fcinf_noimplicitfloat(float %a) #0 {
; CHECK-LABEL: define i1 @f32_fcnan_fcinf_noimplicitfloat(
; CHECK-SAME: float [[A:%.*]]) #[[ATTR1:[0-9]+]] {
Expand All @@ -200,4 +304,44 @@ define i1 @f32_fcnan_fcinf_noimplicitfloat(float %a) #0 {
ret i1 %cmp
}

define i1 @f32_fcposinf_noimplicitfloat(float %a) #0 {
; CHECK-LABEL: define i1 @f32_fcposinf_noimplicitfloat(
; CHECK-SAME: float [[A:%.*]]) #[[ATTR1]] {
; CHECK-NEXT: [[I32:%.*]] = bitcast float [[A]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[I32]], 2139095040
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%cmp = icmp eq i32 %i32, 2139095040
ret i1 %cmp
}

define i1 @f32_fcposnan(float %a) {
; CHECK-LABEL: define i1 @f32_fcposnan(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[I32:%.*]] = bitcast float [[A]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[I32]], 2139095041
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
%cmp = icmp eq i32 %i32, 2139095041
ret i1 %cmp
}

define i1 @f32_fcposinf_multiuse(float %a) {
; CHECK-LABEL: define i1 @f32_fcposinf_multiuse(
; CHECK-SAME: float [[A:%.*]]) {
; CHECK-NEXT: [[I32:%.*]] = bitcast float [[A]] to i32
; CHECK-NEXT: call void @usei32(i32 [[I32]])
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[I32]], 2139095040
; CHECK-NEXT: ret i1 [[CMP]]
;
%i32 = bitcast float %a to i32
call void @usei32(i32 %i32)
%cmp = icmp eq i32 %i32, 2139095040
ret i1 %cmp
}

declare void @usei32(i32)

attributes #0 = { noimplicitfloat }

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