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[SLC] Refactor the simplication of pow() (NFC)

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Use more meaningful variable names.  Mostly NFC.

llvm-svn: 338266
This commit is contained in:
Evandro Menezes 2018-07-30 16:20:04 +00:00
parent 9e86d5852c
commit 04fe04cb47
2 changed files with 117 additions and 114 deletions
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225
lib/Transforms/Utils/SimplifyLibCalls.cpp
View File

@ -1126,72 +1126,75 @@ Value *LibCallSimplifier::replacePowWithSqrt(CallInst *Pow, IRBuilder<> &B) {
if (!Pow->isFast()) if (!Pow->isFast())
return nullptr; return nullptr;
const APFloat *Arg1C; Value *Sqrt, *Base = Pow->getArgOperand(0), *Expo = Pow->getArgOperand(1);
if (!match(Pow->getArgOperand(1), m_APFloat(Arg1C)))
return nullptr;
if (!Arg1C->isExactlyValue(0.5) && !Arg1C->isExactlyValue(-0.5))
return nullptr;
// Fast-math flags from the pow() are propagated to all replacement ops.
IRBuilder<>::FastMathFlagGuard Guard(B);
B.setFastMathFlags(Pow->getFastMathFlags());
Type *Ty = Pow->getType(); Type *Ty = Pow->getType();
Value *Sqrt;
if (Pow->hasFnAttr(Attribute::ReadNone)) {
// We know that errno is never set, so replace with an intrinsic:
// pow(x, 0.5) --> llvm.sqrt(x)
// llvm.pow(x, 0.5) --> llvm.sqrt(x)
auto *F = Intrinsic::getDeclaration(Pow->getModule(), Intrinsic::sqrt, Ty);
Sqrt = B.CreateCall(F, Pow->getArgOperand(0));
} else if (hasUnaryFloatFn(TLI, Ty, LibFunc_sqrt, LibFunc_sqrtf,
LibFunc_sqrtl)) {
// Errno could be set, so we must use a sqrt libcall.
// TODO: We also should check that the target can in fact lower the sqrt
// libcall. We currently have no way to ask this question, so we ask
// whether the target has a sqrt libcall which is not exactly the same.
Sqrt = emitUnaryFloatFnCall(Pow->getArgOperand(0),
TLI->getName(LibFunc_sqrt), B,
Pow->getCalledFunction()->getAttributes());
} else {
// We can't replace with an intrinsic or a libcall.
return nullptr;
}
// If this is pow(x, -0.5), get the reciprocal. const APFloat *ExpoF;
if (Arg1C->isExactlyValue(-0.5)) if (!match(Expo, m_APFloat(ExpoF)) ||
Sqrt = B.CreateFDiv(ConstantFP::get(Ty, 1.0), Sqrt); (!ExpoF->isExactlyValue(0.5) && !ExpoF->isExactlyValue(-0.5)))
return nullptr;
// If errno is never set, then use the intrinsic for sqrt().
if (Pow->hasFnAttr(Attribute::ReadNone)) {
Function *SqrtFn = Intrinsic::getDeclaration(Pow->getModule(),
Intrinsic::sqrt, Ty);
Sqrt = B.CreateCall(SqrtFn, Base);
}
// Otherwise, use the libcall for sqrt().
else if (hasUnaryFloatFn(TLI, Ty,
LibFunc_sqrt, LibFunc_sqrtf, LibFunc_sqrtl)) {
// TODO: We also should check that the target can in fact lower the sqrt()
// libcall. We currently have no way to ask this question, so we ask if
// the target has a sqrt() libcall, which is not exactly the same.
Sqrt = emitUnaryFloatFnCall(Base, TLI->getName(LibFunc_sqrt), B,
Pow->getCalledFunction()->getAttributes());
} else
return nullptr;
// If this is pow(x, -0.5), then get the reciprocal.
if (ExpoF->isNegative())
Sqrt = B.CreateFDiv(ConstantFP::get(Ty, 1.0), Sqrt, "reciprocal");
return Sqrt; return Sqrt;
} }
Value *LibCallSimplifier::optimizePow(CallInst *CI, IRBuilder<> &B) { Value *LibCallSimplifier::optimizePow(CallInst *Pow, IRBuilder<> &B) {
Function *Callee = CI->getCalledFunction(); Value *Base = Pow->getArgOperand(0), *Expo = Pow->getArgOperand(1);
Value *Ret = nullptr; Function *Callee = Pow->getCalledFunction();
AttributeList Attrs = Callee->getAttributes();
StringRef Name = Callee->getName(); StringRef Name = Callee->getName();
if (UnsafeFPShrink && Name == "pow" && hasFloatVersion(Name)) Module *Module = Pow->getModule();
Ret = optimizeUnaryDoubleFP(CI, B, true); Type *Ty = Pow->getType();
Value *Shrunk = nullptr;
bool Ignored;
Value *Op1 = CI->getArgOperand(0), *Op2 = CI->getArgOperand(1); if (UnsafeFPShrink &&
Name == TLI->getName(LibFunc_pow) && hasFloatVersion(Name))
Shrunk = optimizeUnaryDoubleFP(Pow, B, true);
// Propagate math semantics flags from the call to any created instructions.
IRBuilder<>::FastMathFlagGuard Guard(B);
B.setFastMathFlags(Pow->getFastMathFlags());
// Evaluate special cases related to the base.
// pow(1.0, x) -> 1.0 // pow(1.0, x) -> 1.0
if (match(Op1, m_SpecificFP(1.0))) if (match(Base, m_SpecificFP(1.0)))
return Op1; return Base;
// pow(2.0, x) -> llvm.exp2(x)
if (match(Op1, m_SpecificFP(2.0))) { // pow(2.0, x) -> exp2(x)
Value *Exp2 = Intrinsic::getDeclaration(CI->getModule(), Intrinsic::exp2, if (match(Base, m_SpecificFP(2.0))) {
CI->getType()); Value *Exp2 = Intrinsic::getDeclaration(Module, Intrinsic::exp2, Ty);
return B.CreateCall(Exp2, Op2, "exp2"); return B.CreateCall(Exp2, Expo, "exp2");
} }
// There's no llvm.exp10 intrinsic yet, but, maybe, some day there will // There's no exp10 intrinsic yet, but, maybe, some day there shall be one.
// be one. if (ConstantFP *BaseC = dyn_cast<ConstantFP>(Base)) {
if (ConstantFP *Op1C = dyn_cast<ConstantFP>(Op1)) {
// pow(10.0, x) -> exp10(x) // pow(10.0, x) -> exp10(x)
if (Op1C->isExactlyValue(10.0) && if (BaseC->isExactlyValue(10.0) &&
hasUnaryFloatFn(TLI, Op1->getType(), LibFunc_exp10, LibFunc_exp10f, hasUnaryFloatFn(TLI, Ty, LibFunc_exp10, LibFunc_exp10f, LibFunc_exp10l))
LibFunc_exp10l)) return emitUnaryFloatFnCall(Expo, TLI->getName(LibFunc_exp10), B, Attrs);
return emitUnaryFloatFnCall(Op2, TLI->getName(LibFunc_exp10), B,
Callee->getAttributes());
} }
// pow(exp(x), y) -> exp(x * y) // pow(exp(x), y) -> exp(x * y)
@ -1200,91 +1203,91 @@ Value *LibCallSimplifier::optimizePow(CallInst *CI, IRBuilder<> &B) {
// transformation changes overflow and underflow behavior quite dramatically. // transformation changes overflow and underflow behavior quite dramatically.
// Example: x = 1000, y = 0.001. // Example: x = 1000, y = 0.001.
// pow(exp(x), y) = pow(inf, 0.001) = inf, whereas exp(x*y) = exp(1). // pow(exp(x), y) = pow(inf, 0.001) = inf, whereas exp(x*y) = exp(1).
auto *OpC = dyn_cast<CallInst>(Op1); auto *BaseFn = dyn_cast<CallInst>(Base);
if (OpC && OpC->isFast() && CI->isFast()) { if (BaseFn && BaseFn->isFast() && Pow->isFast()) {
LibFunc Func; LibFunc LibFn;
Function *OpCCallee = OpC->getCalledFunction(); Function *CalleeFn = BaseFn->getCalledFunction();
if (OpCCallee && TLI->getLibFunc(OpCCallee->getName(), Func) && if (CalleeFn && TLI->getLibFunc(CalleeFn->getName(), LibFn) &&
TLI->has(Func) && (Func == LibFunc_exp || Func == LibFunc_exp2)) { (LibFn == LibFunc_exp || LibFn == LibFunc_exp2) && TLI->has(LibFn)) {
IRBuilder<>::FastMathFlagGuard Guard(B); IRBuilder<>::FastMathFlagGuard Guard(B);
B.setFastMathFlags(CI->getFastMathFlags()); B.setFastMathFlags(Pow->getFastMathFlags());
Value *FMul = B.CreateFMul(OpC->getArgOperand(0), Op2, "mul");
return emitUnaryFloatFnCall(FMul, OpCCallee->getName(), B, Value *FMul = B.CreateFMul(BaseFn->getArgOperand(0), Expo, "mul");
OpCCallee->getAttributes()); return emitUnaryFloatFnCall(FMul, CalleeFn->getName(), B,
CalleeFn->getAttributes());
} }
} }
if (Value *Sqrt = replacePowWithSqrt(CI, B)) // Evaluate special cases related to the exponent.
if (Value *Sqrt = replacePowWithSqrt(Pow, B))
return Sqrt; return Sqrt;
ConstantFP *Op2C = dyn_cast<ConstantFP>(Op2); ConstantFP *ExpoC = dyn_cast<ConstantFP>(Expo);
if (!Op2C) if (!ExpoC)
return Ret; return Shrunk;
if (Op2C->getValueAPF().isZero()) // pow(x, 0.0) -> 1.0 // pow(x, -1.0) -> 1.0 / x
return ConstantFP::get(CI->getType(), 1.0); if (ExpoC->isExactlyValue(-1.0))
return B.CreateFDiv(ConstantFP::get(Ty, 1.0), Base, "reciprocal");
// pow(x, 0.0) -> 1.0
if (ExpoC->getValueAPF().isZero())
return ConstantFP::get(Ty, 1.0);
// pow(x, 1.0) -> x
if (ExpoC->isExactlyValue(1.0))
return Base;
// pow(x, 2.0) -> x * x
if (ExpoC->isExactlyValue(2.0))
return B.CreateFMul(Base, Base, "square");
// FIXME: Correct the transforms and pull this into replacePowWithSqrt(). // FIXME: Correct the transforms and pull this into replacePowWithSqrt().
if (Op2C->isExactlyValue(0.5) && if (ExpoC->isExactlyValue(0.5) &&
hasUnaryFloatFn(TLI, Op2->getType(), LibFunc_sqrt, LibFunc_sqrtf, hasUnaryFloatFn(TLI, Ty, LibFunc_sqrt, LibFunc_sqrtf, LibFunc_sqrtl)) {
LibFunc_sqrtl)) {
// Expand pow(x, 0.5) to (x == -infinity ? +infinity : fabs(sqrt(x))). // Expand pow(x, 0.5) to (x == -infinity ? +infinity : fabs(sqrt(x))).
// This is faster than calling pow, and still handles negative zero // This is faster than calling pow, and still handles negative zero
// and negative infinity correctly. // and negative infinity correctly.
// TODO: In finite-only mode, this could be just fabs(sqrt(x)). // TODO: In finite-only mode, this could be just fabs(sqrt(x)).
Value *Inf = ConstantFP::getInfinity(CI->getType()); Value *PosInf = ConstantFP::getInfinity(Ty);
Value *NegInf = ConstantFP::getInfinity(CI->getType(), true); Value *NegInf = ConstantFP::getInfinity(Ty, true);
// TODO: As above, we should lower to the sqrt intrinsic if the pow is an // TODO: As above, we should lower to the sqrt() intrinsic if the pow() is
// intrinsic, to match errno semantics. // an intrinsic, to match errno semantics.
Value *Sqrt = emitUnaryFloatFnCall(Op1, "sqrt", B, Callee->getAttributes()); Value *Sqrt = emitUnaryFloatFnCall(Base, TLI->getName(LibFunc_sqrt),
B, Attrs);
Function *FabsFn = Intrinsic::getDeclaration(Module, Intrinsic::fabs, Ty);
Value *FAbs = B.CreateCall(FabsFn, Sqrt, "abs");
Module *M = Callee->getParent(); Value *FCmp = B.CreateFCmpOEQ(Base, NegInf, "isinf");
Function *FabsF = Intrinsic::getDeclaration(M, Intrinsic::fabs, Value *Sel = B.CreateSelect(FCmp, PosInf, FAbs);
CI->getType());
Value *FAbs = B.CreateCall(FabsF, Sqrt);
Value *FCmp = B.CreateFCmpOEQ(Op1, NegInf);
Value *Sel = B.CreateSelect(FCmp, Inf, FAbs);
return Sel; return Sel;
} }
// Propagate fast-math-flags from the call to any created instructions. // pow(x, n) -> x * x * x * ....
IRBuilder<>::FastMathFlagGuard Guard(B); if (Pow->isFast()) {
B.setFastMathFlags(CI->getFastMathFlags()); APFloat ExpoA = abs(ExpoC->getValueAPF());
// pow(x, 1.0) --> x // We limit to a max of 7 fmul(s). Thus the maximum exponent is 32.
if (Op2C->isExactlyValue(1.0))
return Op1;
// pow(x, 2.0) --> x * x
if (Op2C->isExactlyValue(2.0))
return B.CreateFMul(Op1, Op1, "pow2");
// pow(x, -1.0) --> 1.0 / x
if (Op2C->isExactlyValue(-1.0))
return B.CreateFDiv(ConstantFP::get(CI->getType(), 1.0), Op1, "powrecip");
// In -ffast-math, generate repeated fmul instead of generating pow(x, n).
if (CI->isFast()) {
APFloat V = abs(Op2C->getValueAPF());
// We limit to a max of 7 fmul(s). Thus max exponent is 32.
// This transformation applies to integer exponents only. // This transformation applies to integer exponents only.
if (V.compare(APFloat(V.getSemantics(), 32.0)) == APFloat::cmpGreaterThan || if (!ExpoA.isInteger() ||
!V.isInteger()) ExpoA.compare
(APFloat(ExpoA.getSemantics(), 32.0)) == APFloat::cmpGreaterThan)
return nullptr; return nullptr;
// We will memoize intermediate products of the Addition Chain. // We will memoize intermediate products of the Addition Chain.
Value *InnerChain[33] = {nullptr}; Value *InnerChain[33] = {nullptr};
InnerChain[1] = Op1; InnerChain[1] = Base;
InnerChain[2] = B.CreateFMul(Op1, Op1); InnerChain[2] = B.CreateFMul(Base, Base, "square");
// We cannot readily convert a non-double type (like float) to a double. // We cannot readily convert a non-double type (like float) to a double.
// So we first convert V to something which could be converted to double. // So we first convert ExpoA to something which could be converted to double.
bool Ignored; ExpoA.convert(APFloat::IEEEdouble(), APFloat::rmTowardZero, &Ignored);
V.convert(APFloat::IEEEdouble(), APFloat::rmTowardZero, &Ignored);
Value *FMul = getPow(InnerChain, V.convertToDouble(), B); Value *FMul = getPow(InnerChain, ExpoA.convertToDouble(), B);
// For negative exponents simply compute the reciprocal. // For negative exponents simply compute the reciprocal.
if (Op2C->isNegative()) if (ExpoC->isNegative())
FMul = B.CreateFDiv(ConstantFP::get(CI->getType(), 1.0), FMul); FMul = B.CreateFDiv(ConstantFP::get(Ty, 1.0), FMul, "reciprocal");
return FMul; return FMul;
} }

6
test/Transforms/InstCombine/pow-sqrt.ll
View File

@ -20,9 +20,9 @@ define <2 x double> @pow_intrinsic_half_approx(<2 x double> %x) {
define double @pow_libcall_half_approx(double %x) { define double @pow_libcall_half_approx(double %x) {
; CHECK-LABEL: @pow_libcall_half_approx( ; CHECK-LABEL: @pow_libcall_half_approx(
; CHECK-NEXT: [[SQRT:%.*]] = call double @sqrt(double %x) ; CHECK-NEXT: [[SQRT:%.*]] = call afn double @sqrt(double %x)
; CHECK-NEXT: [[TMP1:%.*]] = call double @llvm.fabs.f64(double [[SQRT]]) ; CHECK-NEXT: [[TMP1:%.*]] = call afn double @llvm.fabs.f64(double [[SQRT]])
; CHECK-NEXT: [[TMP2:%.*]] = fcmp oeq double %x, 0xFFF0000000000000 ; CHECK-NEXT: [[TMP2:%.*]] = fcmp afn oeq double %x, 0xFFF0000000000000
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[TMP2]], double 0x7FF0000000000000, double [[TMP1]] ; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[TMP2]], double 0x7FF0000000000000, double [[TMP1]]
; CHECK-NEXT: ret double [[TMP3]] ; CHECK-NEXT: ret double [[TMP3]]
; ;