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Implement a correct ui64->f32 conversion. The old 

one was subject to double rounding in extreme cases.

llvm-svn: 103744
This commit is contained in:
Dale Johannesen 2010-05-13 23:50:42 +00:00
parent 0adc50cd1a
commit 1ae94b9394
1 changed files with 36 additions and 0 deletions
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36
llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
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@ -2026,6 +2026,7 @@ SDValue SelectionDAGLegalize::ExpandLegalINT_TO_FP(bool isSigned,
return Result;
}
assert(!isSigned && "Legalize cannot Expand SINT_TO_FP for i64 yet");
// Code below here assumes !isSigned without checking again.
// Implementation of unsigned i64 to f64 following the algorithm in
// __floatundidf in compiler_rt. This implementation has the advantage
@ -2051,6 +2052,41 @@ SDValue SelectionDAGLegalize::ExpandLegalINT_TO_FP(bool isSigned,
return DAG.getNode(ISD::FADD, dl, MVT::f64, LoFlt, HiSub);
}
// Implementation of unsigned i64 to f32. This implementation has the
// advantage of performing rounding correctly.
// TODO: Generalize this for use with other types.
if (Op0.getValueType() == MVT::i64 && DestVT == MVT::f32) {
EVT SHVT = TLI.getShiftAmountTy();
SDValue And = DAG.getNode(ISD::AND, dl, MVT::i64, Op0,
DAG.getConstant(UINT64_C(0xfffffffffffff800), MVT::i64));
SDValue Or = DAG.getNode(ISD::OR, dl, MVT::i64, And,
DAG.getConstant(UINT64_C(0x800), MVT::i64));
SDValue And2 = DAG.getNode(ISD::AND, dl, MVT::i64, Op0,
DAG.getConstant(UINT64_C(0x7ff), MVT::i64));
SDValue Ne = DAG.getSetCC(dl, TLI.getSetCCResultType(MVT::i64),
And2, DAG.getConstant(UINT64_C(0), MVT::i64), ISD::SETNE);
SDValue Sel = DAG.getNode(ISD::SELECT, dl, MVT::i64, Ne, Or, Op0);
SDValue Ge = DAG.getSetCC(dl, TLI.getSetCCResultType(MVT::i64),
Op0, DAG.getConstant(UINT64_C(0x0020000000000000), MVT::i64),
ISD::SETUGE);
SDValue Sel2 = DAG.getNode(ISD::SELECT, dl, MVT::i64, Ge, Sel, Op0);
SDValue Sh = DAG.getNode(ISD::SRL, dl, MVT::i64, Sel2,
DAG.getConstant(32, SHVT));
SDValue Trunc = DAG.getNode(ISD::TRUNCATE, dl, MVT::i32, Sh);
SDValue Fcvt = DAG.getNode(ISD::UINT_TO_FP, dl, MVT::f64, Trunc);
SDValue TwoP32 =
DAG.getConstantFP(BitsToDouble(UINT64_C(0x41f0000000000000)), MVT::f64);
SDValue Fmul = DAG.getNode(ISD::FMUL, dl, MVT::f64, TwoP32, Fcvt);
SDValue Lo = DAG.getNode(ISD::TRUNCATE, dl, MVT::i32, Sel2);
SDValue Fcvt2 = DAG.getNode(ISD::UINT_TO_FP, dl, MVT::f64, Lo);
SDValue Fadd = DAG.getNode(ISD::FADD, dl, MVT::f64, Fmul, Fcvt2);
return DAG.getNode(ISD::FP_ROUND, dl, MVT::f32, Fadd,
DAG.getIntPtrConstant(0));
}
SDValue Tmp1 = DAG.getNode(ISD::SINT_TO_FP, dl, DestVT, Op0);
SDValue SignSet = DAG.getSetCC(dl, TLI.getSetCCResultType(Op0.getValueType()),