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ValueTracking: Teach computeKnownFPClass that multiply can avoid denormals #171730

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Merged
arsenm merged 1 commit into from
Dec 11, 2025
+29 −11
Merged

ValueTracking: Teach computeKnownFPClass that multiply can avoid denormals #171730

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18 changes: 18 additions & 0 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5646,6 +5646,24 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
KnownFPClass KnownLHS, KnownRHS;
computeKnownFPClass(Op->getOperand(1), DemandedElts, NeedForNan, KnownRHS,
Q, Depth + 1);

const APFloat *CRHS;
if (match(Op->getOperand(1), m_APFloat(CRHS))) {
// Match denormal scaling pattern, similar to the case in ldexp. If the
// constant's exponent is sufficiently large, the result cannot be
// subnormal.

// TODO: Should do general ConstantFPRange analysis.
const fltSemantics &Flt =
Op->getType()->getScalarType()->getFltSemantics();
unsigned Precision = APFloat::semanticsPrecision(Flt);
const int MantissaBits = Precision - 1;

int MinKnownExponent = ilogb(*CRHS);
if (MinKnownExponent >= MantissaBits)
Known.knownNot(fcSubnormal);
}

if (!KnownRHS.isKnownNeverNaN())
break;

Expand Down
20 changes: 10 additions & 10 deletions llvm/test/Transforms/Attributor/nofpclass-fmul.ll
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Expand Up @@ -35,7 +35,7 @@ define float @ret_mul_exponent_f32_22(float %arg0) {
}

define float @ret_mul_exponent_f32_23(float %arg0) {
; CHECK-LABEL: define float @ret_mul_exponent_f32_23(
; CHECK-LABEL: define nofpclass(sub) float @ret_mul_exponent_f32_23(
; CHECK-SAME: float [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul float [[ARG0]], 0x4160000000000000
; CHECK-NEXT: ret float [[CALL]]
Expand All @@ -45,7 +45,7 @@ define float @ret_mul_exponent_f32_23(float %arg0) {
}

define float @ret_mul_exponent_f32_24(float %arg0) {
; CHECK-LABEL: define float @ret_mul_exponent_f32_24(
; CHECK-LABEL: define nofpclass(sub) float @ret_mul_exponent_f32_24(
; CHECK-SAME: float [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul float [[ARG0]], 0x4170000000000000
; CHECK-NEXT: ret float [[CALL]]
Expand All @@ -55,7 +55,7 @@ define float @ret_mul_exponent_f32_24(float %arg0) {
}

define float @ret_mul_exponent_f32_23_nnan(float nofpclass(nan) %arg0) {
; CHECK-LABEL: define nofpclass(nan) float @ret_mul_exponent_f32_23_nnan(
; CHECK-LABEL: define nofpclass(nan sub) float @ret_mul_exponent_f32_23_nnan(
; CHECK-SAME: float nofpclass(nan) [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul float [[ARG0]], 0x4160000000000000
; CHECK-NEXT: ret float [[CALL]]
Expand Down Expand Up @@ -85,7 +85,7 @@ define double @ret_mul_exponent_f64_51(double %arg0) {
}

define double @ret_mul_exponent_f64_52(double %arg0) {
; CHECK-LABEL: define double @ret_mul_exponent_f64_52(
; CHECK-LABEL: define nofpclass(sub) double @ret_mul_exponent_f64_52(
; CHECK-SAME: double [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul double [[ARG0]], 0x4330000000000000
; CHECK-NEXT: ret double [[CALL]]
Expand All @@ -95,7 +95,7 @@ define double @ret_mul_exponent_f64_52(double %arg0) {
}

define double @ret_mul_exponent_f64_53(double %arg0) {
; CHECK-LABEL: define double @ret_mul_exponent_f64_53(
; CHECK-LABEL: define nofpclass(sub) double @ret_mul_exponent_f64_53(
; CHECK-SAME: double [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul double [[ARG0]], 0x4340000000000000
; CHECK-NEXT: ret double [[CALL]]
Expand Down Expand Up @@ -125,7 +125,7 @@ define half @ret_mul_exponent_f16_9(half %arg0) {
}

define half @ret_mul_exponent_f16_10(half %arg0) {
; CHECK-LABEL: define half @ret_mul_exponent_f16_10(
; CHECK-LABEL: define nofpclass(sub) half @ret_mul_exponent_f16_10(
; CHECK-SAME: half [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul half [[ARG0]], 0xH6400
; CHECK-NEXT: ret half [[CALL]]
Expand All @@ -145,7 +145,7 @@ define bfloat @ret_mul_exponent_bf16_6(bfloat %arg0) {
}

define bfloat @ret_mul_exponent_bf16_7(bfloat %arg0) {
; CHECK-LABEL: define bfloat @ret_mul_exponent_bf16_7(
; CHECK-LABEL: define nofpclass(sub) bfloat @ret_mul_exponent_bf16_7(
; CHECK-SAME: bfloat [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul bfloat [[ARG0]], 0xR4300
; CHECK-NEXT: ret bfloat [[CALL]]
Expand All @@ -155,7 +155,7 @@ define bfloat @ret_mul_exponent_bf16_7(bfloat %arg0) {
}

define bfloat @ret_mul_exponent_bf16_8(bfloat %arg0) {
; CHECK-LABEL: define bfloat @ret_mul_exponent_bf16_8(
; CHECK-LABEL: define nofpclass(sub) bfloat @ret_mul_exponent_bf16_8(
; CHECK-SAME: bfloat [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul bfloat [[ARG0]], 0xR4380
; CHECK-NEXT: ret bfloat [[CALL]]
Expand Down Expand Up @@ -215,7 +215,7 @@ define float @ret_mul_exponent_f32_neg127(float %arg0) {
}

define <2 x float> @ret_mul_exponent_v2f32_splat_23(<2 x float> %arg0) {
; CHECK-LABEL: define <2 x float> @ret_mul_exponent_v2f32_splat_23(
; CHECK-LABEL: define nofpclass(sub) <2 x float> @ret_mul_exponent_v2f32_splat_23(
; CHECK-SAME: <2 x float> [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul <2 x float> [[ARG0]], splat (float 0x4160000000000000)
; CHECK-NEXT: ret <2 x float> [[CALL]]
Expand Down Expand Up @@ -267,7 +267,7 @@ define float @ret_mul_f32_0(float %arg0) {
}

define float @ret_mul_f32_inf(float %arg0) {
; CHECK-LABEL: define float @ret_mul_f32_inf(
; CHECK-LABEL: define nofpclass(sub) float @ret_mul_f32_inf(
; CHECK-SAME: float [[ARG0:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[CALL:%.*]] = fmul float [[ARG0]], 0x7FF0000000000000
; CHECK-NEXT: ret float [[CALL]]
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/Attributor/nofpclass-nan-fmul.ll
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Expand Up @@ -195,7 +195,7 @@ define float @ret_fmul_square_nnan_nzero(float nofpclass(nan zero) %arg) #0 {
}

define float @ret_fmul_ieee_inf(float %arg) {
; CHECK-LABEL: define float @ret_fmul_ieee_inf
; CHECK-LABEL: define nofpclass(sub) float @ret_fmul_ieee_inf
; CHECK-SAME: (float [[ARG:%.*]]) #[[ATTR4:[0-9]+]] {
; CHECK-NEXT: [[FMUL:%.*]] = fmul float [[ARG]], 0x7FF0000000000000
; CHECK-NEXT: ret float [[FMUL]]
Expand Down
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