[llvm] [SelectionDAG][x86] Ensure vector reduction optimization (PR #144231)

[Simon Pilgrim via llvm-commits]

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Suhajda =?utf-8?q?Tamás?= <sutajo at gmail.com>,
Suhajda =?utf-8?q?Tamás?= <sutajo at gmail.com>
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In-Reply-To: <llvm.org/llvm/llvm-project/pull/144231 at github.com>


================
@@ -46192,60 +46299,8 @@ static SDValue combineMinMaxReduction(SDNode *Extract, SelectionDAG &DAG,
   if (!Src)
     return SDValue();
 
-  EVT SrcVT = Src.getValueType();
-  EVT SrcSVT = SrcVT.getScalarType();
-  if (SrcSVT != ExtractVT || (SrcVT.getSizeInBits() % 128) != 0)
-    return SDValue();
-
-  SDLoc DL(Extract);
-  SDValue MinPos = Src;
-
-  // First, reduce the source down to 128-bit, applying BinOp to lo/hi.
-  while (SrcVT.getSizeInBits() > 128) {
-    SDValue Lo, Hi;
-    std::tie(Lo, Hi) = splitVector(MinPos, DAG, DL);
-    SrcVT = Lo.getValueType();
-    MinPos = DAG.getNode(BinOp, DL, SrcVT, Lo, Hi);
-  }
-  assert(((SrcVT == MVT::v8i16 && ExtractVT == MVT::i16) ||
-          (SrcVT == MVT::v16i8 && ExtractVT == MVT::i8)) &&
-         "Unexpected value type");
-
-  // PHMINPOSUW applies to UMIN(v8i16), for SMIN/SMAX/UMAX we must apply a mask
-  // to flip the value accordingly.
-  SDValue Mask;
-  unsigned MaskEltsBits = ExtractVT.getSizeInBits();
-  if (BinOp == ISD::SMAX)
-    Mask = DAG.getConstant(APInt::getSignedMaxValue(MaskEltsBits), DL, SrcVT);
-  else if (BinOp == ISD::SMIN)
-    Mask = DAG.getConstant(APInt::getSignedMinValue(MaskEltsBits), DL, SrcVT);
-  else if (BinOp == ISD::UMAX)
-    Mask = DAG.getAllOnesConstant(DL, SrcVT);
-
-  if (Mask)
-    MinPos = DAG.getNode(ISD::XOR, DL, SrcVT, Mask, MinPos);
-
-  // For v16i8 cases we need to perform UMIN on pairs of byte elements,
-  // shuffling each upper element down and insert zeros. This means that the
-  // v16i8 UMIN will leave the upper element as zero, performing zero-extension
-  // ready for the PHMINPOS.
-  if (ExtractVT == MVT::i8) {
-    SDValue Upper = DAG.getVectorShuffle(
-        SrcVT, DL, MinPos, DAG.getConstant(0, DL, MVT::v16i8),
-        {1, 16, 3, 16, 5, 16, 7, 16, 9, 16, 11, 16, 13, 16, 15, 16});
-    MinPos = DAG.getNode(ISD::UMIN, DL, SrcVT, MinPos, Upper);
-  }
-
-  // Perform the PHMINPOS on a v8i16 vector,
-  MinPos = DAG.getBitcast(MVT::v8i16, MinPos);
-  MinPos = DAG.getNode(X86ISD::PHMINPOS, DL, MVT::v8i16, MinPos);
-  MinPos = DAG.getBitcast(SrcVT, MinPos);
-
-  if (Mask)
-    MinPos = DAG.getNode(ISD::XOR, DL, SrcVT, Mask, MinPos);
-
-  return DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, ExtractVT, MinPos,
-                     DAG.getVectorIdxConstant(0, DL));
+  return createMinMaxReduction(Src, ExtractVT, SDLoc(Extract),
----------------
RKSimon wrote:

I've raised #144654

https://github.com/llvm/llvm-project/pull/144231