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-rw-r--r--llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp170
1 files changed, 142 insertions, 28 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 33e70593d15..34a0e04bc05 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -276,6 +276,7 @@ namespace {
SDValue visitFMA(SDNode *N);
SDValue visitFDIV(SDNode *N);
SDValue visitFREM(SDNode *N);
+ SDValue visitFSQRT(SDNode *N);
SDValue visitFCOPYSIGN(SDNode *N);
SDValue visitSINT_TO_FP(SDNode *N);
SDValue visitUINT_TO_FP(SDNode *N);
@@ -326,7 +327,8 @@ namespace {
SDValue BuildSDIV(SDNode *N);
SDValue BuildSDIVPow2(SDNode *N);
SDValue BuildUDIV(SDNode *N);
- SDValue BuildRSQRTE(SDNode *N);
+ SDValue BuildReciprocalEstimate(SDValue Op);
+ SDValue BuildRsqrtEstimate(SDValue Op);
SDValue MatchBSwapHWordLow(SDNode *N, SDValue N0, SDValue N1,
bool DemandHighBits = true);
SDValue MatchBSwapHWord(SDNode *N, SDValue N0, SDValue N1);
@@ -1307,6 +1309,7 @@ SDValue DAGCombiner::visit(SDNode *N) {
case ISD::FMA: return visitFMA(N);
case ISD::FDIV: return visitFDIV(N);
case ISD::FREM: return visitFREM(N);
+ case ISD::FSQRT: return visitFSQRT(N);
case ISD::FCOPYSIGN: return visitFCOPYSIGN(N);
case ISD::SINT_TO_FP: return visitSINT_TO_FP(N);
case ISD::UINT_TO_FP: return visitUINT_TO_FP(N);
@@ -6976,6 +6979,7 @@ SDValue DAGCombiner::visitFDIV(SDNode *N) {
ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);
ConstantFPSDNode *N1CFP = dyn_cast<ConstantFPSDNode>(N1);
EVT VT = N->getValueType(0);
+ SDLoc DL(N);
const TargetOptions &Options = DAG.getTarget().Options;
// fold vector ops
@@ -7007,10 +7011,37 @@ SDValue DAGCombiner::visitFDIV(SDNode *N) {
return DAG.getNode(ISD::FMUL, SDLoc(N), VT, N0,
DAG.getConstantFP(Recip, VT));
}
+
// If this FDIV is part of a reciprocal square root, it may be folded
// into a target-specific square root estimate instruction.
- if (SDValue SqrtOp = BuildRSQRTE(N))
- return SqrtOp;
+ if (N1.getOpcode() == ISD::FSQRT) {
+ if (SDValue RV = BuildRsqrtEstimate(N1.getOperand(0))) {
+ AddToWorklist(RV.getNode());
+ return DAG.getNode(ISD::FMUL, DL, VT, N0, RV);
+ }
+ } else if (N1.getOpcode() == ISD::FP_EXTEND &&
+ N1.getOperand(0).getOpcode() == ISD::FSQRT) {
+ if (SDValue RV = BuildRsqrtEstimate(N1.getOperand(0).getOperand(0))) {
+ AddToWorklist(RV.getNode());
+ RV = DAG.getNode(ISD::FP_EXTEND, SDLoc(N1), VT, RV);
+ AddToWorklist(RV.getNode());
+ return DAG.getNode(ISD::FMUL, DL, VT, N0, RV);
+ }
+ } else if (N1.getOpcode() == ISD::FP_ROUND &&
+ N1.getOperand(0).getOpcode() == ISD::FSQRT) {
+ if (SDValue RV = BuildRsqrtEstimate(N1.getOperand(0).getOperand(0))) {
+ AddToWorklist(RV.getNode());
+ RV = DAG.getNode(ISD::FP_ROUND, SDLoc(N1), VT, RV, N1.getOperand(1));
+ AddToWorklist(RV.getNode());
+ return DAG.getNode(ISD::FMUL, DL, VT, N0, RV);
+ }
+ }
+
+ // Fold into a reciprocal estimate and multiply instead of a real divide.
+ if (SDValue RV = BuildReciprocalEstimate(N1)) {
+ AddToWorklist(RV.getNode());
+ return DAG.getNode(ISD::FMUL, DL, VT, N0, RV);
+ }
}
// (fdiv (fneg X), (fneg Y)) -> (fdiv X, Y)
@@ -7042,6 +7073,33 @@ SDValue DAGCombiner::visitFREM(SDNode *N) {
return SDValue();
}
+SDValue DAGCombiner::visitFSQRT(SDNode *N) {
+ if (DAG.getTarget().Options.UnsafeFPMath) {
+ // Compute this as 1/(1/sqrt(X)): the reciprocal of the reciprocal sqrt.
+ if (SDValue RV = BuildRsqrtEstimate(N->getOperand(0))) {
+ AddToWorklist(RV.getNode());
+ RV = BuildReciprocalEstimate(RV);
+ if (RV.getNode()) {
+ // Unfortunately, RV is now NaN if the input was exactly 0.
+ // Select out this case and force the answer to 0.
+ EVT VT = RV.getValueType();
+
+ SDValue Zero = DAG.getConstantFP(0.0, VT);
+ SDValue ZeroCmp =
+ DAG.getSetCC(SDLoc(N), TLI.getSetCCResultType(*DAG.getContext(), VT),
+ N->getOperand(0), Zero, ISD::SETEQ);
+ AddToWorklist(ZeroCmp.getNode());
+ AddToWorklist(RV.getNode());
+
+ RV = DAG.getNode(VT.isVector() ? ISD::VSELECT : ISD::SELECT,
+ SDLoc(N), VT, ZeroCmp, Zero, RV);
+ return RV;
+ }
+ }
+ }
+ return SDValue();
+}
+
SDValue DAGCombiner::visitFCOPYSIGN(SDNode *N) {
SDValue N0 = N->getOperand(0);
SDValue N1 = N->getOperand(1);
@@ -11702,36 +11760,92 @@ SDValue DAGCombiner::BuildUDIV(SDNode *N) {
return S;
}
-/// Given an ISD::FDIV node with either a direct or indirect ISD::FSQRT operand,
-/// generate a DAG expression using a reciprocal square root estimate op.
-SDValue DAGCombiner::BuildRSQRTE(SDNode *N) {
+SDValue DAGCombiner::BuildReciprocalEstimate(SDValue Op) {
+ if (Level >= AfterLegalizeDAG)
+ return SDValue();
+
// Expose the DAG combiner to the target combiner implementations.
TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
- SDLoc DL(N);
- EVT VT = N->getValueType(0);
- SDValue N1 = N->getOperand(1);
- if (N1.getOpcode() == ISD::FSQRT) {
- if (SDValue RV = TLI.BuildRSQRTE(N1.getOperand(0), DCI)) {
- AddToWorklist(RV.getNode());
- return DAG.getNode(ISD::FMUL, DL, VT, N->getOperand(0), RV);
- }
- } else if (N1.getOpcode() == ISD::FP_EXTEND &&
- N1.getOperand(0).getOpcode() == ISD::FSQRT) {
- if (SDValue RV = TLI.BuildRSQRTE(N1.getOperand(0).getOperand(0), DCI)) {
- DCI.AddToWorklist(RV.getNode());
- RV = DAG.getNode(ISD::FP_EXTEND, SDLoc(N1), VT, RV);
- AddToWorklist(RV.getNode());
- return DAG.getNode(ISD::FMUL, DL, VT, N->getOperand(0), RV);
+ unsigned Iterations;
+ if (SDValue Est = TLI.getEstimate(ISD::FDIV, Op, DCI, Iterations)) {
+ // Newton iteration for a function: F(X) is X_{i+1} = X_i - F(X_i)/F'(X_i)
+ // For the reciprocal, we need to find the zero of the function:
+ // F(X) = A X - 1 [which has a zero at X = 1/A]
+ // =>
+ // X_{i+1} = X_i (2 - A X_i) = X_i + X_i (1 - A X_i) [this second form
+ // does not require additional intermediate precision]
+ EVT VT = Op.getValueType();
+ SDLoc DL(Op);
+ SDValue FPOne = DAG.getConstantFP(1.0, VT);
+
+ AddToWorklist(Est.getNode());
+
+ // Newton iterations: Est = Est + Est (1 - Arg * Est)
+ for (unsigned i = 0; i < Iterations; ++i) {
+ SDValue NewEst = DAG.getNode(ISD::FMUL, DL, VT, Op, Est);
+ AddToWorklist(NewEst.getNode());
+
+ NewEst = DAG.getNode(ISD::FSUB, DL, VT, FPOne, NewEst);
+ AddToWorklist(NewEst.getNode());
+
+ NewEst = DAG.getNode(ISD::FMUL, DL, VT, Est, NewEst);
+ AddToWorklist(NewEst.getNode());
+
+ Est = DAG.getNode(ISD::FADD, DL, VT, Est, NewEst);
+ AddToWorklist(Est.getNode());
}
- } else if (N1.getOpcode() == ISD::FP_ROUND &&
- N1.getOperand(0).getOpcode() == ISD::FSQRT) {
- if (SDValue RV = TLI.BuildRSQRTE(N1.getOperand(0).getOperand(0), DCI)) {
- DCI.AddToWorklist(RV.getNode());
- RV = DAG.getNode(ISD::FP_ROUND, SDLoc(N1), VT, RV, N1.getOperand(1));
- AddToWorklist(RV.getNode());
- return DAG.getNode(ISD::FMUL, DL, VT, N->getOperand(0), RV);
+
+ return Est;
+ }
+
+ return SDValue();
+}
+
+SDValue DAGCombiner::BuildRsqrtEstimate(SDValue Op) {
+ if (Level >= AfterLegalizeDAG)
+ return SDValue();
+
+ // Expose the DAG combiner to the target combiner implementations.
+ TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
+ unsigned Iterations;
+ if (SDValue Est = TLI.getEstimate(ISD::FSQRT, Op, DCI, Iterations)) {
+ // Newton iteration for a function: F(X) is X_{i+1} = X_i - F(X_i)/F'(X_i)
+ // For the reciprocal sqrt, we need to find the zero of the function:
+ // F(X) = 1/X^2 - A [which has a zero at X = 1/sqrt(A)]
+ // =>
+ // X_{i+1} = X_i (1.5 - A X_i^2 / 2)
+ // As a result, we precompute A/2 prior to the iteration loop.
+ EVT VT = Op.getValueType();
+ SDLoc DL(Op);
+ SDValue FPThreeHalves = DAG.getConstantFP(1.5, VT);
+
+ AddToWorklist(Est.getNode());
+
+ // We now need 0.5 * Arg which we can write as (1.5 * Arg - Arg) so that
+ // this entire sequence requires only one FP constant.
+ SDValue HalfArg = DAG.getNode(ISD::FMUL, DL, VT, FPThreeHalves, Op);
+ AddToWorklist(HalfArg.getNode());
+
+ HalfArg = DAG.getNode(ISD::FSUB, DL, VT, HalfArg, Op);
+ AddToWorklist(HalfArg.getNode());
+
+ // Newton iterations: Est = Est * (1.5 - HalfArg * Est * Est)
+ for (unsigned i = 0; i < Iterations; ++i) {
+ SDValue NewEst = DAG.getNode(ISD::FMUL, DL, VT, Est, Est);
+ AddToWorklist(NewEst.getNode());
+
+ NewEst = DAG.getNode(ISD::FMUL, DL, VT, HalfArg, NewEst);
+ AddToWorklist(NewEst.getNode());
+
+ NewEst = DAG.getNode(ISD::FSUB, DL, VT, FPThreeHalves, NewEst);
+ AddToWorklist(NewEst.getNode());
+
+ Est = DAG.getNode(ISD::FMUL, DL, VT, Est, NewEst);
+ AddToWorklist(Est.getNode());
}
+
+ return Est;
}
return SDValue();
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