Reapply "[CodeGen][X86] Expand USUBSAT to UMAX+SUB, also for vectors"

Related to https://bugs.llvm.org/show_bug.cgi?id=40123.

Rather than scalarizing, expand a vector USUBSAT into UMAX+SUB,
which produces much better code for X86.

Reapplying with updated SLPVectorizer tests.

Differential Revision: https://reviews.llvm.org/D56636

llvm-svn: 351219

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
index 6e0bc97..4923a52 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
@@ -141,6 +141,7 @@ class VectorLegalizer {
   SDValue ExpandFunnelShift(SDValue Op);
   SDValue ExpandROT(SDValue Op);
   SDValue ExpandFMINNUM_FMAXNUM(SDValue Op);
+  SDValue ExpandAddSubSat(SDValue Op);
   SDValue ExpandStrictFPOp(SDValue Op);
 
   /// Implements vector promotion.
@@ -777,6 +778,11 @@ SDValue VectorLegalizer::Expand(SDValue Op) {
   case ISD::FMINNUM:
   case ISD::FMAXNUM:
     return ExpandFMINNUM_FMAXNUM(Op);
+  case ISD::USUBSAT:
+  case ISD::SSUBSAT:
+  case ISD::UADDSAT:
+  case ISD::SADDSAT:
+    return ExpandAddSubSat(Op);
   case ISD::STRICT_FADD:
   case ISD::STRICT_FSUB:
   case ISD::STRICT_FMUL:
@@ -1206,6 +1212,12 @@ SDValue VectorLegalizer::ExpandFMINNUM_FMAXNUM(SDValue Op) {
   return DAG.UnrollVectorOp(Op.getNode());
 }
 
+SDValue VectorLegalizer::ExpandAddSubSat(SDValue Op) {
+  if (SDValue Expanded = TLI.expandAddSubSat(Op.getNode(), DAG))
+    return Expanded;
+  return DAG.UnrollVectorOp(Op.getNode());
+}
+
 SDValue VectorLegalizer::ExpandStrictFPOp(SDValue Op) {
   EVT VT = Op.getValueType();
   EVT EltVT = VT.getVectorElementType();