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[InstCombine] pow(C,x) -> exp2(log2(C)*x) 

Summary:
Transform
pow(C,x) 

To
exp2(log2(C)*x) 

if C > 0, C != inf, C != NaN (and C is not power of 2, since we have some fold for such case already).

log(C) is folded by the compiler and exp2 is much faster to compute than pow.

Reviewers: spatel, efriedma, evandro

Reviewed By: evandro

Subscribers: lebedev.ri, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64099

llvm-svn: 365637
This commit is contained in:
David Bolvansky 2019-07-10 14:43:27 +00:00
parent 9cd82a4fbd
commit 0735cc1954
3 changed files with 64 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -1235,7 +1235,8 @@ static Value *getPow(Value *InnerChain[33], unsigned Exp, IRBuilder<> &B) {
}
/// Use exp{,2}(x * y) for pow(exp{,2}(x), y);
/// exp2(n * x) for pow(2.0 ** n, x); exp10(x) for pow(10.0, x).
/// exp2(n * x) for pow(2.0 ** n, x); exp10(x) for pow(10.0, x);
/// exp2(log2(C)*x) for pow(C,x).
Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilder<> &B) {
Value *Base = Pow->getArgOperand(0), *Expo = Pow->getArgOperand(1);
AttributeList Attrs = Pow->getCalledFunction()->getAttributes();
@ -1347,6 +1348,28 @@ Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilder<> &B) {
return emitUnaryFloatFnCall(Expo, TLI, LibFunc_exp10, LibFunc_exp10f,
LibFunc_exp10l, B, Attrs);
// pow(C,x) -> exp2(log2(C)*x)
if (Pow->hasOneUse() && Pow->hasApproxFunc() && Pow->hasNoNaNs() &&
Pow->hasNoInfs() && BaseF->isNormal() && !BaseF->isNegative()) {
Value *Log = nullptr;
if (Ty->isFloatTy())
Log = ConstantFP::get(Ty, std::log2(BaseF->convertToFloat()));
else if (Ty->isDoubleTy())
Log = ConstantFP::get(Ty, std::log2(BaseF->convertToDouble()));
if (Log) {
Value *FMul = B.CreateFMul(Log, Expo, "mul");
if (Pow->doesNotAccessMemory()) {
return B.CreateCall(Intrinsic::getDeclaration(Mod, Intrinsic::exp2, Ty),
FMul, "exp2");
} else {
if (hasUnaryFloatFn(TLI, Ty, LibFunc_exp2, LibFunc_exp2f,
LibFunc_exp2l))
return emitUnaryFloatFnCall(FMul, TLI, LibFunc_exp2, LibFunc_exp2f,
LibFunc_exp2l, B, Attrs);
}
}
}
return nullptr;
}

49
llvm/test/Transforms/InstCombine/pow-exp.ll
View File

@ -205,13 +205,16 @@ define double @function_pointer(double ()* %fptr, double %p1) {
ret double %pow
}
; pow(C,x) -> exp2(log2(C)*x)
declare void @use_d(double)
declare void @use_f(float)
define double @pow_ok_base(double %e) {
; CHECK-LABEL: @pow_ok_base(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn double @pow(double 0x3FE6666666666666, double [[E:%.*]])
; CHECK-NEXT: ret double [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn double [[E:%.*]], 0xBFE0776228967D13
; CHECK-NEXT: [[EXP2:%.*]] = call nnan ninf afn double @exp2(double [[MUL]])
; CHECK-NEXT: ret double [[EXP2]]
;
%call = tail call afn nnan ninf double @pow(double 0x3FE6666666666666, double %e)
ret double %call
@ -219,8 +222,9 @@ define double @pow_ok_base(double %e) {
define double @pow_ok_base_fast(double %e) {
; CHECK-LABEL: @pow_ok_base_fast(
; CHECK-NEXT: [[CALL:%.*]] = tail call fast double @pow(double 0x3FE6666666666666, double [[E:%.*]])
; CHECK-NEXT: ret double [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul fast double [[E:%.*]], 0xBFE0776228967D13
; CHECK-NEXT: [[EXP2:%.*]] = call fast double @exp2(double [[MUL]])
; CHECK-NEXT: ret double [[EXP2]]
;
%call = tail call fast double @pow(double 0x3FE6666666666666, double %e)
ret double %call
@ -228,8 +232,9 @@ define double @pow_ok_base_fast(double %e) {
define double @pow_ok_base2(double %e) {
; CHECK-LABEL: @pow_ok_base2(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn double @pow(double 1.770000e+01, double [[E:%.*]])
; CHECK-NEXT: ret double [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn double [[E:%.*]], 0x4010952C788751AC
; CHECK-NEXT: [[EXP2:%.*]] = call nnan ninf afn double @exp2(double [[MUL]])
; CHECK-NEXT: ret double [[EXP2]]
;
%call = tail call afn nnan ninf double @pow(double 1.770000e+01, double %e)
ret double %call
@ -237,8 +242,9 @@ define double @pow_ok_base2(double %e) {
define double @pow_ok_base3(double %e) {
; CHECK-LABEL: @pow_ok_base3(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn double @pow(double 1.010000e+01, double [[E:%.*]])
; CHECK-NEXT: ret double [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn double [[E:%.*]], 0x400AB0B5584886CD
; CHECK-NEXT: [[EXP2:%.*]] = call nnan ninf afn double @exp2(double [[MUL]])
; CHECK-NEXT: ret double [[EXP2]]
;
%call = tail call afn nnan ninf double @pow(double 1.010000e+01, double %e)
ret double %call
@ -246,8 +252,9 @@ define double @pow_ok_base3(double %e) {
define double @pow_ok_ten_base(double %e) {
; CHECK-LABEL: @pow_ok_ten_base(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn double @pow(double 1.000000e+01, double [[E:%.*]])
; CHECK-NEXT: ret double [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn double [[E:%.*]], 0x400A934F0979A371
; CHECK-NEXT: [[EXP2:%.*]] = call nnan ninf afn double @exp2(double [[MUL]])
; CHECK-NEXT: ret double [[EXP2]]
;
%call = tail call afn nnan ninf double @pow(double 1.000000e+01, double %e)
ret double %call
@ -255,8 +262,9 @@ define double @pow_ok_ten_base(double %e) {
define float @powf_ok_base(float %e) {
; CHECK-LABEL: @powf_ok_base(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn float @powf(float 0x3FE6666660000000, float [[E:%.*]])
; CHECK-NEXT: ret float [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn float [[E:%.*]], 0xBFE0776240000000
; CHECK-NEXT: [[EXP2F:%.*]] = call nnan ninf afn float @exp2f(float [[MUL]])
; CHECK-NEXT: ret float [[EXP2F]]
;
%call = tail call afn nnan ninf float @powf(float 0x3FE6666660000000, float %e)
ret float %call
@ -264,8 +272,9 @@ define float @powf_ok_base(float %e) {
define float @powf_ok_base2(float %e) {
; CHECK-LABEL: @powf_ok_base2(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn float @powf(float 0x4031B33340000000, float [[E:%.*]])
; CHECK-NEXT: ret float [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn float [[E:%.*]], 0x4010952C80000000
; CHECK-NEXT: [[EXP2F:%.*]] = call nnan ninf afn float @exp2f(float [[MUL]])
; CHECK-NEXT: ret float [[EXP2F]]
;
%call = tail call afn nnan ninf float @powf(float 0x4031B33340000000, float %e)
ret float %call
@ -273,8 +282,9 @@ define float @powf_ok_base2(float %e) {
define float @powf_ok_base3(float %e) {
; CHECK-LABEL: @powf_ok_base3(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn float @powf(float 0x4024333340000000, float [[E:%.*]])
; CHECK-NEXT: ret float [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn float [[E:%.*]], 0x400AB0B560000000
; CHECK-NEXT: [[EXP2F:%.*]] = call nnan ninf afn float @exp2f(float [[MUL]])
; CHECK-NEXT: ret float [[EXP2F]]
;
%call = tail call afn nnan ninf float @powf(float 0x4024333340000000, float %e)
ret float %call
@ -282,13 +292,16 @@ define float @powf_ok_base3(float %e) {
define float @powf_ok_ten_base(float %e) {
; CHECK-LABEL: @powf_ok_ten_base(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn float @powf(float 1.000000e+01, float [[E:%.*]])
; CHECK-NEXT: ret float [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn float [[E:%.*]], 0x400A934F00000000
; CHECK-NEXT: [[EXP2F:%.*]] = call nnan ninf afn float @exp2f(float [[MUL]])
; CHECK-NEXT: ret float [[EXP2F]]
;
%call = tail call afn nnan ninf float @powf(float 1.000000e+01, float %e)
ret float %call
}
; Negative tests
define double @pow_zero_base(double %e) {
; CHECK-LABEL: @pow_zero_base(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn double @pow(double 0.000000e+00, double [[E:%.*]])

15
llvm/test/Transforms/InstCombine/pow_fp_int.ll
View File

@ -196,8 +196,9 @@ define double @powf_exp_const2_int_fast(double %base) {
define double @pow_uitofp_const_base_fast_i32(i32 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_fast_i32(
; CHECK-NEXT: [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
; CHECK-NEXT: [[POW:%.*]] = tail call fast float @llvm.pow.f32(float 7.000000e+00, float [[SUBFP]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[POW]] to double
; CHECK-NEXT: [[MUL:%.*]] = fmul fast float [[SUBFP]], 0x4006757680000000
; CHECK-NEXT: [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[MUL]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[EXP2]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = uitofp i32 %x to float
@ -247,8 +248,9 @@ define double @pow_uitofp_double_base_fast_i32(double %base, i32 %x) {
define double @pow_sitofp_const_base_fast_i64(i64 %x) {
; CHECK-LABEL: @pow_sitofp_const_base_fast_i64(
; CHECK-NEXT: [[SUBFP:%.*]] = sitofp i64 [[X:%.*]] to float
; CHECK-NEXT: [[POW:%.*]] = tail call fast float @llvm.pow.f32(float 7.000000e+00, float [[SUBFP]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[POW]] to double
; CHECK-NEXT: [[MUL:%.*]] = fmul fast float [[SUBFP]], 0x4006757680000000
; CHECK-NEXT: [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[MUL]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[EXP2]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = sitofp i64 %x to float
@ -260,8 +262,9 @@ define double @pow_sitofp_const_base_fast_i64(i64 %x) {
define double @pow_uitofp_const_base_fast_i64(i64 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_fast_i64(
; CHECK-NEXT: [[SUBFP:%.*]] = uitofp i64 [[X:%.*]] to float
; CHECK-NEXT: [[POW:%.*]] = tail call fast float @llvm.pow.f32(float 7.000000e+00, float [[SUBFP]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[POW]] to double
; CHECK-NEXT: [[MUL:%.*]] = fmul fast float [[SUBFP]], 0x4006757680000000
; CHECK-NEXT: [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[MUL]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[EXP2]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = uitofp i64 %x to float