[PATCH] D28982: DAG: Do not scalarize fsub if fneg is legal

[Matt Arsenault via Phabricator via llvm-commits]

arsenm updated this revision to Diff 87844.
arsenm added a comment.

Address comments


https://reviews.llvm.org/D28982

Files:
  lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp


Index: lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
+++ lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
@@ -105,6 +105,7 @@
   SDValue ExpandLoad(SDValue Op);
   SDValue ExpandStore(SDValue Op);
   SDValue ExpandFNEG(SDValue Op);
+  SDValue ExpandFSUB(SDValue Op);
   SDValue ExpandBITREVERSE(SDValue Op);
   SDValue ExpandCTLZ(SDValue Op);
   SDValue ExpandCTTZ_ZERO_UNDEF(SDValue Op);
@@ -691,6 +692,8 @@
     return ExpandUINT_TO_FLOAT(Op);
   case ISD::FNEG:
     return ExpandFNEG(Op);
+  case ISD::FSUB:
+    return ExpandFSUB(Op);
   case ISD::SETCC:
     return UnrollVSETCC(Op);
   case ISD::BITREVERSE:
@@ -1021,6 +1024,18 @@
   return DAG.UnrollVectorOp(Op.getNode());
 }
 
+SDValue VectorLegalizer::ExpandFSUB(SDValue Op) {
+  // For floating-point values, (a-b) is the same as a+(-b). If FNEG is legal,
+  // we can defer this to operation legalization where it will be lowered as
+  // a+(-b).
+  EVT VT = Op.getValueType();
+  if (TLI.isOperationLegalOrCustom(ISD::FNEG, VT) &&
+      TLI.isOperationLegalOrCustom(ISD::FADD, VT))
+    return Op; // Defer to LegalizeDAG
+
+  return DAG.UnrollVectorOp(Op.getNode());
+}
+
 SDValue VectorLegalizer::ExpandCTLZ(SDValue Op) {
   EVT VT = Op.getValueType();
   unsigned NumBitsPerElt = VT.getScalarSizeInBits();


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