Use rsqrt (X86) to speed up reciprocal square root calcs
This is a first step for generating SSE rsqrt instructions for
reciprocal square root calcs when fast-math is allowed.
For now, be conservative and only enable this for AMD btver2
where performance improves significantly - for example, 29%
on llvm/projects/test-suite/SingleSource/Benchmarks/BenchmarkGame/n-body.c
(if we convert the data type to single-precision float).
This patch adds a two constant version of the Newton-Raphson
refinement algorithm to DAGCombiner that can be selected by any target
via a parameter returned by getRsqrtEstimate()..
See PR20900 for more details:
http://llvm.org/bugs/show_bug.cgi?id=20900
Differential Revision: http://reviews.llvm.org/D5658
llvm-svn: 220570
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index ef357f4..72d3a59 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -7466,7 +7466,8 @@
SDValue PPCTargetLowering::getRsqrtEstimate(SDValue Operand,
DAGCombinerInfo &DCI,
- unsigned &RefinementSteps) const {
+ unsigned &RefinementSteps,
+ bool &UseOneConstNR) const {
EVT VT = Operand.getValueType();
if ((VT == MVT::f32 && Subtarget.hasFRSQRTES()) ||
(VT == MVT::f64 && Subtarget.hasFRSQRTE()) ||
@@ -7479,6 +7480,7 @@
RefinementSteps = Subtarget.hasRecipPrec() ? 1 : 3;
if (VT.getScalarType() == MVT::f64)
++RefinementSteps;
+ UseOneConstNR = true;
return DCI.DAG.getNode(PPCISD::FRSQRTE, SDLoc(Operand), VT, Operand);
}
return SDValue();