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[SimplifyLibCalls] pow(x, -0.5) -> 1.0 / sqrt(x). 

Differential Revision:  https://reviews.llvm.org/D28479

llvm-svn: 291486
This commit is contained in:
Davide Italiano 2017-01-09 21:55:23 +00:00
parent d4b24eda73
commit 472684eaf5
2 changed files with 28 additions and 1 deletions
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18
llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -1074,6 +1074,24 @@ Value *LibCallSimplifier::optimizePow(CallInst *CI, IRBuilder<> &B) {
if (Op2C->getValueAPF().isZero()) // pow(x, 0.0) -> 1.0
return ConstantFP::get(CI->getType(), 1.0);
if (Op2C->isExactlyValue(-0.5) &&
hasUnaryFloatFn(TLI, Op2->getType(), LibFunc::sqrt, LibFunc::sqrtf,
LibFunc::sqrtl)) {
// If -ffast-math:
// pow(x, -0.5) -> 1.0 / sqrt(x)
if (CI->hasUnsafeAlgebra()) {
IRBuilder<>::FastMathFlagGuard Guard(B);
B.setFastMathFlags(CI->getFastMathFlags());
// Here we cannot lower to an intrinsic because C99 sqrt() and llvm.sqrt
// are not guaranteed to have the same semantics.
Value *Sqrt = emitUnaryFloatFnCall(Op1, TLI->getName(LibFunc::sqrt), B,
Callee->getAttributes());
return B.CreateFDiv(ConstantFP::get(CI->getType(), 1.0), Sqrt, "sqrtrecip");
}
}
if (Op2C->isExactlyValue(0.5) &&
hasUnaryFloatFn(TLI, Op2->getType(), LibFunc::sqrt, LibFunc::sqrtf,
LibFunc::sqrtl) &&

11
llvm/test/Transforms/InstCombine/pow-sqrt.ll
View File

@ -9,5 +9,14 @@ define double @pow_half(double %x) {
; CHECK-NEXT: %sqrt = call fast double @sqrt(double %x)
; CHECK-NEXT: ret double %sqrt
declare double @llvm.pow.f64(double, double)
define double @pow_neghalf(double %x) {
%pow = call fast double @llvm.pow.f64(double %x, double -5.000000e-01)
ret double %pow
}
; CHECK-LABEL: define double @pow_neghalf(
; CHECK-NEXT: %sqrt = call fast double @sqrt(double %x) #0
; CHECK-NEXT: %sqrtrecip = fdiv fast double 1.000000e+00, %sqrt
; CHECK-NEXT: ret double %sqrtrecip
declare double @llvm.pow.f64(double, double)