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Add support for 6-, 12-, and 18-bit limited precision calculations of exp for

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floating-point numbers.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56023 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2008-09-09 22:13:54 +00:00
parent 7258737a11
commit b4ec283049
1 changed files with 134 additions and 7 deletions
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141
lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
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@ -2761,7 +2761,7 @@ GetSignificand(SelectionDAG &DAG, SDValue Op) {
static SDValue
GetExponent(SelectionDAG &DAG, SDValue Op) {
SDValue t1 = DAG.getNode(ISD::AND, MVT::i32, Op,
DAG.getConstant(0x7f800000, MVT::i32));
DAG.getConstant(0x7f800000, MVT::i32));
SDValue t2 = DAG.getNode(ISD::SRL, MVT::i32, t1,
DAG.getConstant(23, MVT::i32));
SDValue t3 = DAG.getNode(ISD::SUB, MVT::i32, t2,
@ -2784,15 +2784,142 @@ SelectionDAGLowering::implVisitBinaryAtomic(CallInst& I, ISD::NodeType Op) {
return 0;
}
/// visitExp - lower an exp intrinsic. Handles the special sequences
/// for limited-precision mode.
/// visitExp - Lower an exp intrinsic. Handles the special sequences for
/// limited-precision mode.
void
SelectionDAGLowering::visitExp(CallInst &I) {
SDValue result;
// No special expansion.
result = DAG.getNode(ISD::FEXP,
getValue(I.getOperand(1)).getValueType(),
getValue(I.getOperand(1)));
if (getValue(I.getOperand(1)).getValueType() == MVT::f32 &&
LimitFloatPrecision > 0 && LimitFloatPrecision <= 18) {
SDValue Op = getValue(I.getOperand(1));
// Put the exponent in the right bit position for later addition to the
// final result:
//
// #define LOG2OFe 1.4426950f
// IntegerPartOfX = ((int32_t)(X * LOG2OFe));
SDValue t0 = DAG.getNode(ISD::FMUL, MVT::f32, Op,
DAG.getConstantFP(APFloat(
APInt(32, 0x3fb8aa3b)), MVT::f32));
SDValue IntegerPartOfX = DAG.getNode(ISD::FP_TO_SINT, MVT::i32, t0);
// FractionalPartOfX = (X * LOG2OFe) - (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 TwoToFracPartOfX = DAG.getNode(ISD::BIT_CONVERT, MVT::i32, t5);
// Add the exponent into the result in integer domain.
SDValue t6 = DAG.getNode(ISD::ADD, MVT::i32,
TwoToFracPartOfX, IntegerPartOfX);
result = DAG.getNode(ISD::BIT_CONVERT, MVT::f32, t6);
} 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;
//
// 0.000107046256 error, 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 TwoToFracPartOfX = DAG.getNode(ISD::BIT_CONVERT, MVT::i32, t7);
// Add the exponent into the result in integer domain.
SDValue t8 = DAG.getNode(ISD::ADD, MVT::i32,
TwoToFracPartOfX, IntegerPartOfX);
result = DAG.getNode(ISD::BIT_CONVERT, MVT::f32, t8);
} 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 TwoToFracPartOfX = DAG.getNode(ISD::BIT_CONVERT, MVT::i32, t13);
// Add the exponent into the result in integer domain.
SDValue t14 = DAG.getNode(ISD::ADD, MVT::i32,
TwoToFracPartOfX, IntegerPartOfX);
result = DAG.getNode(ISD::BIT_CONVERT, MVT::f32, t14);
}
} else {
// No special expansion.
result = DAG.getNode(ISD::FEXP,
getValue(I.getOperand(1)).getValueType(),
getValue(I.getOperand(1)));
}
setValue(&I, result);
}