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Transform pow(x, 0.5) to (x == -inf ? inf : fabs(sqrt(x))), which is

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typically faster then doing a general pow.

llvm-svn: 82819
This commit is contained in:
Dan Gohman 2009-09-25 23:10:17 +00:00
parent 01b2c857ed
commit d564cd42d9
2 changed files with 52 additions and 15 deletions
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34
lib/Transforms/Scalar/SimplifyLibCalls.cpp
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@ -95,7 +95,8 @@ public:
/// 'floor'). This function is known to take a single of type matching 'Op'
/// and returns one value with the same type. If 'Op' is a long double, 'l'
/// is added as the suffix of name, if 'Op' is a float, we add a 'f' suffix.
Value *EmitUnaryFloatFnCall(Value *Op, const char *Name, IRBuilder<> &B);
Value *EmitUnaryFloatFnCall(Value *Op, const char *Name, IRBuilder<> &B,
const AttrListPtr &Attrs);
/// EmitPutChar - Emit a call to the putchar function. This assumes that Char
/// is an integer.
@ -221,7 +222,8 @@ Value *LibCallOptimization::EmitMemSet(Value *Dst, Value *Val,
/// returns one value with the same type. If 'Op' is a long double, 'l' is
/// added as the suffix of name, if 'Op' is a float, we add a 'f' suffix.
Value *LibCallOptimization::EmitUnaryFloatFnCall(Value *Op, const char *Name,
IRBuilder<> &B) {
IRBuilder<> &B,
const AttrListPtr &Attrs) {
char NameBuffer[20];
if (Op->getType() != Type::getDoubleTy(*Context)) {
// If we need to add a suffix, copy into NameBuffer.
@ -240,7 +242,7 @@ Value *LibCallOptimization::EmitUnaryFloatFnCall(Value *Op, const char *Name,
Value *Callee = M->getOrInsertFunction(Name, Op->getType(),
Op->getType(), NULL);
CallInst *CI = B.CreateCall(Callee, Op, Name);
CI->setAttributes(Attrs);
if (const Function *F = dyn_cast<Function>(Callee->stripPointerCasts()))
CI->setCallingConv(F->getCallingConv());
@ -1017,7 +1019,7 @@ struct PowOpt : public LibCallOptimization {
if (Op1C->isExactlyValue(1.0)) // pow(1.0, x) -> 1.0
return Op1C;
if (Op1C->isExactlyValue(2.0)) // pow(2.0, x) -> exp2(x)
return EmitUnaryFloatFnCall(Op2, "exp2", B);
return EmitUnaryFloatFnCall(Op2, "exp2", B, CI->getAttributes());
}
ConstantFP *Op2C = dyn_cast<ConstantFP>(Op2);
@ -1027,16 +1029,18 @@ struct PowOpt : public LibCallOptimization {
return ConstantFP::get(CI->getType(), 1.0);
if (Op2C->isExactlyValue(0.5)) {
// FIXME: This is not safe for -0.0 and -inf. This can only be done when
// 'unsafe' math optimizations are allowed.
// x pow(x, 0.5) sqrt(x)
// ---------------------------------------------
// -0.0 +0.0 -0.0
// -inf +inf NaN
#if 0
// pow(x, 0.5) -> sqrt(x)
return B.CreateCall(get_sqrt(), Op1, "sqrt");
#endif
// Expand pow(x, 0.5) to (x == -infinity ? +infinity : fabs(sqrt(x))).
// This is faster than calling pow, and still handles negative zero
// and negative infinite correctly.
// TODO: In fast-math mode, this could be just sqrt(x).
// TODO: In finite-only mode, this could be just fabs(sqrt(x)).
Value *Inf = ConstantFP::getInf(CI->getType());
Value *NegInf = ConstantFP::getInf(CI->getType(), true);
Value *Sqrt = EmitUnaryFloatFnCall(Op1, "sqrt", B, CI->getAttributes());
Value *FAbs = EmitUnaryFloatFnCall(Sqrt, "fabs", B, CI->getAttributes());
Value *FCmp = B.CreateFCmpOEQ(Op1, NegInf, "tmp");
Value *Sel = B.CreateSelect(FCmp, Inf, FAbs, "tmp");
return Sel;
}
if (Op2C->isExactlyValue(1.0)) // pow(x, 1.0) -> x
@ -1117,7 +1121,7 @@ struct UnaryDoubleFPOpt : public LibCallOptimization {
// floor((double)floatval) -> (double)floorf(floatval)
Value *V = Cast->getOperand(0);
V = EmitUnaryFloatFnCall(V, Callee->getName().data(), B);
V = EmitUnaryFloatFnCall(V, Callee->getName().data(), B, CI->getAttributes());
return B.CreateFPExt(V, Type::getDoubleTy(*Context));
}
};

33
test/Transforms/SimplifyLibCalls/pow-to-sqrt.ll Normal file
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@ -0,0 +1,33 @@
; RUN: opt < %s -simplify-libcalls -S | FileCheck %s
; rdar://7235530
; SimplifyLibcalls should optimize pow(x, 0.5) to sqrt plus code to handle
; special cases. The readonly attribute on the call should be preserved.
; CHECK: define float @foo(float %x) nounwind {
; CHECK: %sqrtf = call float @sqrtf(float %x) readonly
; CHECK: %fabsf = call float @fabsf(float %sqrtf) readonly
; CHECK: %tmp = fcmp oeq float %x, 0xFFF0000000000000
; CHECK: %tmp1 = select i1 %tmp, float 0x7FF0000000000000, float %fabsf
; CHECK: ret float %tmp1
define float @foo(float %x) nounwind {
%retval = call float @powf(float %x, float 0.5) readonly
ret float %retval
}
; CHECK: define double @doo(double %x) nounwind {
; CHECK: %sqrt = call double @sqrt(double %x) readonly
; CHECK: %fabs = call double @fabs(double %sqrt) readonly
; CHECK: %tmp = fcmp oeq double %x, 0xFFF0000000000000
; CHECK: %tmp1 = select i1 %tmp, double 0x7FF0000000000000, double %fabs
; CHECK: ret double %tmp1
; CHECK: }
define double @doo(double %x) nounwind {
%retval = call double @pow(double %x, double 0.5) readonly
ret double %retval
}
declare float @powf(float, float) nounwind readonly
declare double @pow(double, double) nounwind readonly