[llvm] [PowerPC] Use rldimi/rlwimi to optimize build_vector (PR #67640)

[Matt Arsenault via llvm-commits]

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@@ -9276,6 +9276,49 @@ bool llvm::checkConvertToNonDenormSingle(APFloat &ArgAPFloat) {
   return (!LosesInfo && !APFloatToConvert.isDenormal());
 }
 
+// Use rldimi/rlwimi to construct vectors:
+//   i32 = (i8 << 24) | (i8 << 16) | (i8 << 8) | i
+//   i32 = (i16 << 16) | i16
+//   i64 = (i32 << 32) | i32
+// And put two i64 together to get a vector.
+static SDValue tryMaskInsertVector(SDValue Op, SelectionDAG &DAG,
+                                   bool LittleEndian) {
+  EVT VT = Op.getValueType();
+  SDLoc dl(Op);
+
+  // There are already patterns for v4i32 and v2i64 construction.
+  if (VT == MVT::v16i8 || VT == MVT::v8i16) {
+    int NumElt = VT.getVectorNumElements();
+    int ScalarSize = VT.getScalarSizeInBits();
+    int EltsFor32 = NumElt / 4;
+    SDValue NewVecElts[4];
+    SDValue Parts[4];
+    for (int i = 0; i < 4; ++i) {
+      for (int j = 0; j < EltsFor32; ++j) {
+        SDValue Elt = LittleEndian
+                          ? Op.getOperand(i * EltsFor32 + EltsFor32 - j - 1)
+                          : Op.getOperand(i * EltsFor32 + j);
+        Parts[j] = DAG.getZExtOrTrunc(Elt, dl, MVT::i32);
+
+        // Left-shift elements to insert, except the last, because offset is 0.
+        if (j != EltsFor32 - 1)
+          Parts[j] =
+              DAG.getNode(ISD::SHL, dl, MVT::i32, Parts[j],
+                          DAG.getTargetConstant(
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arsenm wrote:

You should not use target constants with arbitrary nodes 

https://github.com/llvm/llvm-project/pull/67640