[llvm] [AArch64][SVE] Rework VECTOR_COMPRESS lowering (PR #171162)

[Paul Walker via llvm-commits]

================
@@ -7411,133 +7414,58 @@ SDValue AArch64TargetLowering::LowerLOAD(SDValue Op,
   return SDValue();
 }
 
-// Convert to ContainerVT with no-op casts where possible.
-static SDValue convertToSVEContainerType(SDLoc DL, SDValue Vec, EVT ContainerVT,
-                                         SelectionDAG &DAG) {
-  EVT VecVT = Vec.getValueType();
-  if (VecVT.isFloatingPoint()) {
-    // Use no-op casts for floating-point types.
-    EVT PackedVT = getPackedSVEVectorVT(VecVT.getScalarType());
-    Vec = DAG.getNode(AArch64ISD::REINTERPRET_CAST, DL, PackedVT, Vec);
-    Vec = DAG.getNode(AArch64ISD::NVCAST, DL, ContainerVT, Vec);
-  } else {
-    // Extend integers (may not be a no-op).
-    Vec = DAG.getNode(ISD::ANY_EXTEND, DL, ContainerVT, Vec);
-  }
-  return Vec;
-}
+SDValue AArch64TargetLowering::LowerFixedLengthVectorCompressToSVE(
+    SDValue Op, SelectionDAG &DAG) const {
+  SDLoc DL(Op);
+  EVT VT = Op.getValueType();
 
-// Convert to VecVT with no-op casts where possible.
-static SDValue convertFromSVEContainerType(SDLoc DL, SDValue Vec, EVT VecVT,
-                                           SelectionDAG &DAG) {
-  if (VecVT.isFloatingPoint()) {
-    // Use no-op casts for floating-point types.
-    EVT PackedVT = getPackedSVEVectorVT(VecVT.getScalarType());
-    Vec = DAG.getNode(AArch64ISD::NVCAST, DL, PackedVT, Vec);
-    Vec = DAG.getNode(AArch64ISD::REINTERPRET_CAST, DL, VecVT, Vec);
-  } else {
-    // Truncate integers (may not be a no-op).
-    Vec = DAG.getNode(ISD::TRUNCATE, DL, VecVT, Vec);
-  }
-  return Vec;
+  EVT ContainerVT = getContainerForFixedLengthVector(DAG, VT);
+  SDValue Vec = convertToScalableVector(DAG, ContainerVT, Op.getOperand(0));
+  SDValue Mask = convertFixedMaskToScalableVector(Op.getOperand(1), DAG);
+  SDValue Passthru =
+      convertToScalableVector(DAG, ContainerVT, Op.getOperand(2));
+
+  SDValue Result =
+      DAG.getNode(ISD::VECTOR_COMPRESS, DL, ContainerVT, Vec, Mask, Passthru);
+  return convertFromScalableVector(DAG, VT, Result);
 }
 
 SDValue AArch64TargetLowering::LowerVECTOR_COMPRESS(SDValue Op,
                                                     SelectionDAG &DAG) const {
   SDLoc DL(Op);
-  SDValue Vec = Op.getOperand(0);
-  SDValue Mask = Op.getOperand(1);
-  SDValue Passthru = Op.getOperand(2);
-  EVT VecVT = Vec.getValueType();
-  EVT MaskVT = Mask.getValueType();
-  EVT ElmtVT = VecVT.getVectorElementType();
-  const bool IsFixedLength = VecVT.isFixedLengthVector();
-  const bool HasPassthru = !Passthru.isUndef();
-  unsigned MinElmts = VecVT.getVectorElementCount().getKnownMinValue();
-  EVT FixedVecVT = MVT::getVectorVT(ElmtVT.getSimpleVT(), MinElmts);
-
-  assert(VecVT.isVector() && "Input to VECTOR_COMPRESS must be vector.");
+  EVT VT = Op.getValueType();
+  if (VT.isFixedLengthVector())
+    return LowerFixedLengthVectorCompressToSVE(Op, DAG);
----------------
paulwalker-arm wrote:

While we should not get here when SVE is not available, I'd still move the fixed length handling after the `isSVEAvailable` check because if it does happen at least common code can expand the fixed length variant.

https://github.com/llvm/llvm-project/pull/171162