[Target] remove TargetRecip class; 2nd try

This is a retry of r284495 which was reverted at r284513 due to use-after-scope bugs
caused by faulty usage of StringRef.

This version also renames a pair of functions:
getRecipEstimateDivEnabled()
getRecipEstimateSqrtEnabled()
as suggested by Eric Christopher.

original commit msg:

[Target] remove TargetRecip class; move reciprocal estimate isel functionality to TargetLowering

This is a follow-up to https://reviews.llvm.org/D24816 - where we changed reciprocal estimates to be function attributes
rather than TargetOptions.

This patch is intended to be a structural, but not functional change. By moving all of the
TargetRecip functionality into TargetLowering, we can remove all of the reciprocal estimate
state, shield the callers from the string format implementation, and simplify/localize the
logic needed for a target to enable this.

If a function has a "reciprocal-estimates" attribute, those settings may override the target's
default reciprocal preferences for whatever operation and data type we're trying to optimize.
If there's no attribute string or specific setting for the op/type pair, just use the target
default settings.

As noted earlier, a better solution would be to move the reciprocal estimate settings to IR
instructions and SDNodes rather than function attributes, but that's a multi-step job that
requires infrastructure improvements. I intend to work on that, but it's not clear how long
it will take to get all the pieces in place.

Differential Revision: https://reviews.llvm.org/D25440

llvm-svn: 284746

1 files changed, 34 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index e50fbac0d2a..81886941009 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -14862,11 +14862,21 @@ SDValue DAGCombiner::BuildReciprocalEstimate(SDValue Op, SDNodeFlags *Flags) {
   if (Level >= AfterLegalizeDAG)
     return SDValue();
 
-  // Expose the DAG combiner to the target combiner implementations.
-  TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
+  // TODO: Handle half and/or extended types?
+  EVT VT = Op.getValueType();
+  if (VT.getScalarType() != MVT::f32 && VT.getScalarType() != MVT::f64)
+    return SDValue();
 
-  unsigned Iterations = 0;
-  if (SDValue Est = TLI.getRecipEstimate(Op, DCI, Iterations)) {
+  // If estimates are explicitly disabled for this function, we're done.
+  MachineFunction &MF = DAG.getMachineFunction();
+  int Enabled = TLI.getRecipEstimateDivEnabled(VT, MF);
+  if (Enabled == TLI.ReciprocalEstimate::Disabled)
+    return SDValue();
+
+  // Estimates may be explicitly enabled for this type with a custom number of
+  // refinement steps.
+  int Iterations = TLI.getDivRefinementSteps(VT, MF);
+  if (SDValue Est = TLI.getRecipEstimate(Op, DAG, Enabled, Iterations)) {
     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:
@@ -14881,7 +14891,7 @@ SDValue DAGCombiner::BuildReciprocalEstimate(SDValue Op, SDNodeFlags *Flags) {
       AddToWorklist(Est.getNode());
 
       // Newton iterations: Est = Est + Est (1 - Arg * Est)
-      for (unsigned i = 0; i < Iterations; ++i) {
+      for (int i = 0; i < Iterations; ++i) {
         SDValue NewEst = DAG.getNode(ISD::FMUL, DL, VT, Op, Est, Flags);
         AddToWorklist(NewEst.getNode());
 
@@ -15003,16 +15013,29 @@ SDValue DAGCombiner::buildSqrtEstimateImpl(SDValue Op, SDNodeFlags *Flags,
   if (Level >= AfterLegalizeDAG)
     return SDValue();
 
-  // Expose the DAG combiner to the target combiner implementations.
-  TargetLowering::DAGCombinerInfo DCI(DAG, Level, false, this);
-  unsigned Iterations = 0;
+  // TODO: Handle half and/or extended types?
+  EVT VT = Op.getValueType();
+  if (VT.getScalarType() != MVT::f32 && VT.getScalarType() != MVT::f64)
+    return SDValue();
+
+  // If estimates are explicitly disabled for this function, we're done.
+  MachineFunction &MF = DAG.getMachineFunction();
+  int Enabled = TLI.getRecipEstimateSqrtEnabled(VT, MF);
+  if (Enabled == TLI.ReciprocalEstimate::Disabled)
+    return SDValue();
+
+  // Estimates may be explicitly enabled for this type with a custom number of
+  // refinement steps.
+  int Iterations = TLI.getSqrtRefinementSteps(VT, MF);
+
   bool UseOneConstNR = false;
-  if (SDValue Est = TLI.getRsqrtEstimate(Op, DCI, Iterations, UseOneConstNR)) {
+  if (SDValue Est =
+      TLI.getRsqrtEstimate(Op, DAG, Enabled, Iterations, UseOneConstNR)) {
     AddToWorklist(Est.getNode());
     if (Iterations) {
       Est = UseOneConstNR
-                ? buildSqrtNROneConst(Op, Est, Iterations, Flags, Reciprocal)
-                : buildSqrtNRTwoConst(Op, Est, Iterations, Flags, Reciprocal);
+      ? buildSqrtNROneConst(Op, Est, Iterations, Flags, Reciprocal)
+      : buildSqrtNRTwoConst(Op, Est, Iterations, Flags, Reciprocal);
     }
     return Est;
   }