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[InstCombine] Allow denormal C in pow(C,y) -> exp2(log2(C)*y) 

We check that C is finite and strictly positive, but there's no need to
check that it's normal too. exp2 should be just as accurate on denormals
as pow is.

Differential Revision: https://reviews.llvm.org/D79413
This commit is contained in:
Jay Foad 2020-05-05 13:32:59 +01:00
parent 9d53db2aa0
commit 22829ab5fa
2 changed files with 7 additions and 5 deletions
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2
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -1565,7 +1565,7 @@ Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilderBase &B) {
// pow(n, x) -> exp2(log2(n) * x)
if (Pow->hasApproxFunc() && Pow->hasNoNaNs() && Pow->hasNoInfs() &&
BaseF->isNormal() && !BaseF->isNegative()) {
BaseF->isFiniteNonZero() && !BaseF->isNegative()) {
Value *Log = nullptr;
if (Ty->isFloatTy())
Log = ConstantFP::get(Ty, std::log2(BaseF->convertToFloat()));

10
llvm/test/Transforms/InstCombine/pow-exp.ll
View File

@ -263,8 +263,9 @@ define double @pow_ok_ten_base(double %e) {
define double @pow_ok_denorm_base(double %e) {
; CHECK-LABEL: @pow_ok_denorm_base(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn double @pow(double 0xFFFFFFFF, double [[E:%.*]])
; CHECK-NEXT: ret double [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn double [[E:%.*]], 0xC0904800000005C5
; 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 0x00000000FFFFFFFF, double %e)
ret double %call
@ -312,8 +313,9 @@ define float @powf_ok_ten_base(float %e) {
define float @powf_ok_denorm_base(float %e) {
; CHECK-LABEL: @powf_ok_denorm_base(
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan ninf afn float @powf(float 0x3780000000000000, float [[E:%.*]])
; CHECK-NEXT: ret float [[CALL]]
; CHECK-NEXT: [[MUL:%.*]] = fmul nnan ninf afn float [[E:%.*]], -1.350000e+02
; 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 0x3780000000000000, float %e)
ret float %call