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Use the target-specified iteration count to opt out of any further refinement of an estimate. NFC.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218700 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel 2014-09-30 20:44:23 +00:00
parent cafc85bf1e
commit 73a335f7f6
1 changed files with 60 additions and 58 deletions
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118
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -11778,35 +11778,36 @@ SDValue DAGCombiner::BuildReciprocalEstimate(SDValue Op) {
// Expose the DAG combiner to the target combiner implementations.
TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
unsigned Iterations;
unsigned Iterations = 0;
if (SDValue Est = TLI.getRecipEstimate(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);
if (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());
}
// 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());
}
}
return Est;
}
@ -11819,43 +11820,44 @@ SDValue DAGCombiner::BuildRsqrtEstimate(SDValue Op) {
// Expose the DAG combiner to the target combiner implementations.
TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
unsigned Iterations;
unsigned Iterations = 0;
if (SDValue Est = TLI.getRsqrtEstimate(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);
if (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());
}
// 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;
}