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Implement "visitPow". This is mainly used to see if we have a pow() call of this

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form:

          powf(10.0f, x);

If this is the case, and also we want limited precision floating-point
calculations, then lower to do the limited-precision stuff.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56035 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2008-09-10 00:20:20 +00:00
parent 9d24ac56e1
commit aeb5c7b353
2 changed files with 146 additions and 4 deletions
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149
lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
View File

@ -3400,6 +3400,150 @@ SelectionDAGLowering::visitExp2(CallInst &I) {
setValue(&I, result);
}
/// visitPow - Lower a pow intrinsic. Handles the special sequences for
/// limited-precision mode with x == 10.0f.
void
SelectionDAGLowering::visitPow(CallInst &I) {
SDValue result;
Value *Val = I.getOperand(1);
bool IsExp10 = false;
if (getValue(Val).getValueType() == MVT::f32 &&
LimitFloatPrecision > 0 && LimitFloatPrecision <= 18) {
if (Constant *C = const_cast<Constant*>(dyn_cast<Constant>(Val))) {
if (ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
APFloat Ten(10.0f);
IsExp10 = CFP->getValueAPF().bitwiseIsEqual(Ten);
}
}
}
if (IsExp10 && LimitFloatPrecision > 0 && LimitFloatPrecision <= 18) {
SDValue Op = getValue(I.getOperand(2));
// Put the exponent in the right bit position for later addition to the
// final result:
//
// #define LOG2OF10 3.3219281f
// IntegerPartOfX = (int32_t)(x * LOG2OF10);
SDValue t0 = DAG.getNode(ISD::FMUL, MVT::f32, Op,
DAG.getConstantFP(APFloat(
APInt(32, 0x40549a78)), MVT::f32));
SDValue IntegerPartOfX = DAG.getNode(ISD::FP_TO_SINT, MVT::i32, t0);
// FractionalPartOfX = x - (float)IntegerPartOfX;
SDValue t1 = DAG.getNode(ISD::SINT_TO_FP, MVT::f32, IntegerPartOfX);
SDValue X = DAG.getNode(ISD::FSUB, MVT::f32, t0, t1);
// IntegerPartOfX <<= 23;
IntegerPartOfX = DAG.getNode(ISD::SHL, MVT::i32, IntegerPartOfX,
DAG.getConstant(23, MVT::i32));
if (LimitFloatPrecision <= 6) {
// For floating-point precision of 6:
//
// twoToFractionalPartOfX =
// 0.997535578f +
// (0.735607626f + 0.252464424f * x) * x;
//
// error 0.0144103317, which is 6 bits
SDValue t2 = DAG.getNode(ISD::FMUL, MVT::f32, X,
DAG.getConstantFP(APFloat(
APInt(32, 0x3e814304)), MVT::f32));
SDValue t3 = DAG.getNode(ISD::FADD, MVT::f32, t2,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f3c50c8)), MVT::f32));
SDValue t4 = DAG.getNode(ISD::FMUL, MVT::f32, t3, X);
SDValue t5 = DAG.getNode(ISD::FADD, MVT::f32, t4,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f7f5e7e)), MVT::f32));
SDValue t6 = DAG.getNode(ISD::BIT_CONVERT, MVT::i32, t5);
SDValue TwoToFractionalPartOfX =
DAG.getNode(ISD::ADD, MVT::i32, t6, IntegerPartOfX);
result = DAG.getNode(ISD::BIT_CONVERT, MVT::f32, TwoToFractionalPartOfX);
} else if (LimitFloatPrecision > 6 && LimitFloatPrecision <= 12) {
// For floating-point precision of 12:
//
// TwoToFractionalPartOfX =
// 0.999892986f +
// (0.696457318f +
// (0.224338339f + 0.792043434e-1f * x) * x) * x;
//
// error 0.000107046256, which is 13 to 14 bits
SDValue t2 = DAG.getNode(ISD::FMUL, MVT::f32, X,
DAG.getConstantFP(APFloat(
APInt(32, 0x3da235e3)), MVT::f32));
SDValue t3 = DAG.getNode(ISD::FADD, MVT::f32, t2,
DAG.getConstantFP(APFloat(
APInt(32, 0x3e65b8f3)), MVT::f32));
SDValue t4 = DAG.getNode(ISD::FMUL, MVT::f32, t3, X);
SDValue t5 = DAG.getNode(ISD::FADD, MVT::f32, t4,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f324b07)), MVT::f32));
SDValue t6 = DAG.getNode(ISD::FMUL, MVT::f32, t5, X);
SDValue t7 = DAG.getNode(ISD::FADD, MVT::f32, t6,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f7ff8fd)), MVT::f32));
SDValue t8 = DAG.getNode(ISD::BIT_CONVERT, MVT::i32, t7);
SDValue TwoToFractionalPartOfX =
DAG.getNode(ISD::ADD, MVT::i32, t8, IntegerPartOfX);
result = DAG.getNode(ISD::BIT_CONVERT, MVT::f32, TwoToFractionalPartOfX);
} else { // LimitFloatPrecision > 12 && LimitFloatPrecision <= 18
// For floating-point precision of 18:
//
// TwoToFractionalPartOfX =
// 0.999999982f +
// (0.693148872f +
// (0.240227044f +
// (0.554906021e-1f +
// (0.961591928e-2f +
// (0.136028312e-2f + 0.157059148e-3f *x)*x)*x)*x)*x)*x;
// error 2.47208000*10^(-7), which is better than 18 bits
SDValue t2 = DAG.getNode(ISD::FMUL, MVT::f32, X,
DAG.getConstantFP(APFloat(
APInt(32, 0x3924b03e)), MVT::f32));
SDValue t3 = DAG.getNode(ISD::FADD, MVT::f32, t2,
DAG.getConstantFP(APFloat(
APInt(32, 0x3ab24b87)), MVT::f32));
SDValue t4 = DAG.getNode(ISD::FMUL, MVT::f32, t3, X);
SDValue t5 = DAG.getNode(ISD::FADD, MVT::f32, t4,
DAG.getConstantFP(APFloat(
APInt(32, 0x3c1d8c17)), MVT::f32));
SDValue t6 = DAG.getNode(ISD::FMUL, MVT::f32, t5, X);
SDValue t7 = DAG.getNode(ISD::FADD, MVT::f32, t6,
DAG.getConstantFP(APFloat(
APInt(32, 0x3d634a1d)), MVT::f32));
SDValue t8 = DAG.getNode(ISD::FMUL, MVT::f32, t7, X);
SDValue t9 = DAG.getNode(ISD::FADD, MVT::f32, t8,
DAG.getConstantFP(APFloat(
APInt(32, 0x3e75fe14)), MVT::f32));
SDValue t10 = DAG.getNode(ISD::FMUL, MVT::f32, t9, X);
SDValue t11 = DAG.getNode(ISD::FADD, MVT::f32, t10,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f317234)), MVT::f32));
SDValue t12 = DAG.getNode(ISD::FMUL, MVT::f32, t11, X);
SDValue t13 = DAG.getNode(ISD::FADD, MVT::f32, t12,
DAG.getConstantFP(APFloat(
APInt(32, 0x3f800000)), MVT::f32));
SDValue t14 = DAG.getNode(ISD::BIT_CONVERT, MVT::i32, t13);
SDValue TwoToFractionalPartOfX =
DAG.getNode(ISD::ADD, MVT::i32, t14, IntegerPartOfX);
result = DAG.getNode(ISD::BIT_CONVERT, MVT::f32, TwoToFractionalPartOfX);
}
} else {
// No special expansion.
result = DAG.getNode(ISD::FPOW,
getValue(I.getOperand(1)).getValueType(),
getValue(I.getOperand(1)),
getValue(I.getOperand(2)));
}
setValue(&I, result);
}
/// visitIntrinsicCall - Lower the call to the specified intrinsic function. If
/// we want to emit this as a call to a named external function, return the name
/// otherwise lower it and return null.
@ -3686,10 +3830,7 @@ SelectionDAGLowering::visitIntrinsicCall(CallInst &I, unsigned Intrinsic) {
visitExp2(I);
return 0;
case Intrinsic::pow:
setValue(&I, DAG.getNode(ISD::FPOW,
getValue(I.getOperand(1)).getValueType(),
getValue(I.getOperand(1)),
getValue(I.getOperand(2))));
visitPow(I);
return 0;
case Intrinsic::pcmarker: {
SDValue Tmp = getValue(I.getOperand(1));

1
lib/CodeGen/SelectionDAG/SelectionDAGBuild.h
View File

@ -505,6 +505,7 @@ private:
const char *visitIntrinsicCall(CallInst &I, unsigned Intrinsic);
void visitTargetIntrinsic(CallInst &I, unsigned Intrinsic);
void visitPow(CallInst &I);
void visitExp2(CallInst &I);
void visitExp(CallInst &I);
void visitLog(CallInst &I);