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[InstCombine] Expand the simplification of pow() into exp2()
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Generalize the simplification of `pow(2.0, y)` to `pow(2.0 ** n, y)` for all
scalar and vector types.

This improvement helps some benchmarks in SPEC CPU2000 and CPU2006, such as
252.eon, 447.dealII, 453.povray.  Otherwise, no significant regressions on
x86-64 or A64.

Differential revision: https://reviews.llvm.org/D49273

llvm-svn: 340947
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Evandro Menezes committed Aug 29, 2018
1 parent a2eee47 commit a3a7b53
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Showing 2 changed files with 42 additions and 22 deletions.
30 changes: 25 additions & 5 deletions llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View file
Expand Up @@ -13,6 +13,7 @@
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/SimplifyLibCalls.h"
#include "llvm/ADT/APSInt.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Triple.h"
Expand Down Expand Up @@ -1183,12 +1184,13 @@ static Value *getPow(Value *InnerChain[33], unsigned Exp, IRBuilder<> &B) {
}

/// Use exp{,2}(x * y) for pow(exp{,2}(x), y);
/// exp2(x) for pow(2.0, x); exp10(x) for pow(10.0, x).
/// exp2(n * x) for pow(2.0 ** n, x); exp10(x) for pow(10.0, x).
Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilder<> &B) {
Value *Base = Pow->getArgOperand(0), *Expo = Pow->getArgOperand(1);
AttributeList Attrs = Pow->getCalledFunction()->getAttributes();
Module *Mod = Pow->getModule();
Type *Ty = Pow->getType();
bool Ignored;

// Evaluate special cases related to a nested function as the base.

Expand Down Expand Up @@ -1232,10 +1234,28 @@ Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilder<> &B) {

// Evaluate special cases related to a constant base.

// pow(2.0, x) -> exp2(x)
if (match(Base, m_SpecificFP(2.0))) {
Value *Exp2 = Intrinsic::getDeclaration(Mod, Intrinsic::exp2, Ty);
return B.CreateCall(Exp2, Expo, "exp2");
const APFloat *BaseF;
if (!match(Pow->getArgOperand(0), m_APFloat(BaseF)))
return nullptr;

// pow(2.0 ** n, x) -> exp2(n * x)
APFloat BaseR = APFloat(1.0);
BaseR.convert(BaseF->getSemantics(), APFloat::rmTowardZero, &Ignored);
BaseR = BaseR / *BaseF;
bool IsInteger = BaseF->isInteger(),
IsReciprocal = BaseR.isInteger();
const APFloat *NF = IsReciprocal ? &BaseR : BaseF;
APSInt NI(64, false);
if ((IsInteger || IsReciprocal) &&
!NF->convertToInteger(NI, APFloat::rmTowardZero, &Ignored) &&
NI > 1 && NI.isPowerOf2()) {
double N = NI.logBase2() * (IsReciprocal ? -1.0 : 1.0);
Value *FMul = B.CreateFMul(Expo, ConstantFP::get(Ty, N), "mul");
if (Pow->doesNotAccessMemory())
return B.CreateCall(Intrinsic::getDeclaration(Mod, Intrinsic::exp2, Ty),
FMul, "exp2");
else
return emitUnaryFloatFnCall(FMul, TLI->getName(LibFunc_exp2), B, Attrs);
}

// pow(10.0, x) -> exp10(x)
Expand Down
34 changes: 17 additions & 17 deletions llvm/test/Transforms/InstCombine/pow-1.ll
View file
Expand Up @@ -16,6 +16,7 @@

declare float @powf(float, float) nounwind readonly
declare double @pow(double, double) nounwind readonly
declare double @llvm.pow.f64(double, double)
declare <2 x float> @llvm.pow.v2f32(<2 x float>, <2 x float>) nounwind readonly
declare <2 x double> @llvm.pow.v2f64(<2 x double>, <2 x double>) nounwind readonly

Expand Down Expand Up @@ -57,18 +58,18 @@ define <2 x double> @test_simplify2v(<2 x double> %x) {

define float @test_simplify3(float %x) {
; ANY-LABEL: @test_simplify3(
; ANY-NEXT: [[EXP2:%.*]] = call float @llvm.exp2.f32(float [[X:%.*]])
; ANY-NEXT: ret float [[EXP2]]
; ANY-NEXT: [[EXP2F:%.*]] = call float @exp2f(float [[X:%.*]]) [[NUW_RO:#[0-9]+]]
; ANY-NEXT: ret float [[EXP2F]]
;
%retval = call float @powf(float 2.0, float %x)
ret float %retval
}

; TODO: Should result in exp2(-2.0 * x).
define double @test_simplify3n(double %x) {
; ANY-LABEL: @test_simplify3n(
; ANY-NEXT: [[RETVAL:%.*]] = call double @pow(double 2.500000e-01, double [[X:%.*]])
; ANY-NEXT: ret double [[RETVAL]]
; ANY-NEXT: [[MUL:%.*]] = fmul double [[X:%.*]], -2.000000e+00
; ANY-NEXT: [[EXP2:%.*]] = call double @exp2(double [[MUL]]) [[NUW_RO]]
; ANY-NEXT: ret double [[EXP2]]
;
%retval = call double @pow(double 0.25, double %x)
ret double %retval
Expand All @@ -83,30 +84,30 @@ define <2 x float> @test_simplify3v(<2 x float> %x) {
ret <2 x float> %retval
}

; TODO: Should result in exp2(2.0 * x).
define <2 x double> @test_simplify3vn(<2 x double> %x) {
; ANY-LABEL: @test_simplify3vn(
; ANY-NEXT: [[RETVAL:%.*]] = call <2 x double> @llvm.pow.v2f64(<2 x double> <double 4.000000e+00, double 4.000000e+00>, <2 x double> [[X:%.*]])
; ANY-NEXT: ret <2 x double> [[RETVAL]]
; ANY-NEXT: [[MUL:%.*]] = fmul <2 x double> [[X:%.*]], <double 2.000000e+00, double 2.000000e+00>
; ANY-NEXT: [[EXP2:%.*]] = call <2 x double> @llvm.exp2.v2f64(<2 x double> [[MUL]])
; ANY-NEXT: ret <2 x double> [[EXP2]]
;
%retval = call <2 x double> @llvm.pow.v2f64(<2 x double> <double 4.0, double 4.0>, <2 x double> %x)
ret <2 x double> %retval
}

define double @test_simplify4(double %x) {
; ANY-LABEL: @test_simplify4(
; ANY-NEXT: [[EXP2:%.*]] = call double @llvm.exp2.f64(double [[X:%.*]])
; ANY-NEXT: [[EXP2:%.*]] = call double @exp2(double [[X:%.*]]) [[NUW_RO]]
; ANY-NEXT: ret double [[EXP2]]
;
%retval = call double @pow(double 2.0, double %x)
ret double %retval
}

; TODO: Should result in exp2f(3.0 * x).
define float @test_simplify4n(float %x) {
; ANY-LABEL: @test_simplify4n(
; ANY-NEXT: [[RETVAL:%.*]] = call float @powf(float 8.000000e+00, float [[X:%.*]])
; ANY-NEXT: ret float [[RETVAL]]
; ANY-NEXT: [[MUL:%.*]] = fmul float [[X:%.*]], 3.000000e+00
; ANY-NEXT: [[EXP2F:%.*]] = call float @exp2f(float [[MUL]]) [[NUW_RO]]
; ANY-NEXT: ret float [[EXP2F]]
;
%retval = call float @powf(float 8.0, float %x)
ret float %retval
Expand All @@ -121,11 +122,11 @@ define <2 x double> @test_simplify4v(<2 x double> %x) {
ret <2 x double> %retval
}

; TODO: Should result in exp2f(-x).
define <2 x float> @test_simplify4vn(<2 x float> %x) {
; ANY-LABEL: @test_simplify4vn(
; ANY-NEXT: [[RETVAL:%.*]] = call <2 x float> @llvm.pow.v2f32(<2 x float> <float 5.000000e-01, float 5.000000e-01>, <2 x float> [[X:%.*]])
; ANY-NEXT: ret <2 x float> [[RETVAL]]
; ANY-NEXT: [[MUL:%.*]] = fsub <2 x float> <float -0.000000e+00, float -0.000000e+00>, [[X:%.*]]
; ANY-NEXT: [[EXP2:%.*]] = call <2 x float> @llvm.exp2.v2f32(<2 x float> [[MUL]])
; ANY-NEXT: ret <2 x float> [[EXP2]]
;
%retval = call <2 x float> @llvm.pow.v2f32(<2 x float> <float 0.5, float 0.5>, <2 x float> %x)
ret <2 x float> %retval
Expand Down Expand Up @@ -169,7 +170,7 @@ define <2 x double> @test_simplify6v(<2 x double> %x) {

define float @test_simplify7(float %x) {
; ANY-LABEL: @test_simplify7(
; ANY-NEXT: [[SQRTF:%.*]] = call float @sqrtf(float [[X:%.*]]) [[NUW_RO:#[0-9]+]]
; ANY-NEXT: [[SQRTF:%.*]] = call float @sqrtf(float [[X:%.*]]) [[NUW_RO]]
; ANY-NEXT: [[ABS:%.*]] = call float @llvm.fabs.f32(float [[SQRTF]])
; ANY-NEXT: [[ISINF:%.*]] = fcmp oeq float [[X]], 0xFFF0000000000000
; ANY-NEXT: [[TMP1:%.*]] = select i1 [[ISINF]], float 0x7FF0000000000000, float [[ABS]]
Expand Down Expand Up @@ -330,7 +331,6 @@ define <2 x double> @pow_neg1_double_fastv(<2 x double> %x) {
ret <2 x double> %r
}

declare double @llvm.pow.f64(double %Val, double %Power)
define double @test_simplify17(double %x) {
; ANY-LABEL: @test_simplify17(
; ANY-NEXT: [[SQRT:%.*]] = call double @llvm.sqrt.f64(double [[X:%.*]])
Expand Down

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