[llvm] [PowerPC] Fix vector_shuffle combines when inputs are scalar_to_vector of differing types. (PR #80784)

[Amy Kwan via llvm-commits]

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@@ -15519,33 +15556,33 @@ SDValue PPCTargetLowering::combineVectorShuffle(ShuffleVectorSDNode *SVN,
     // the value into element zero. Since scalar size of LHS and RHS may differ
     // after isScalarToVec, this should be checked using their own sizes.
     if (SToVLHS) {
-      if (!IsLittleEndian && SToVLHS.getValueType().getScalarSizeInBits() >= 64)
+      int LHSScalarSize = SToVLHS.getValueType().getScalarSizeInBits();
+      if (!IsLittleEndian && LHSScalarSize >= 64)
         return Res;
-      // Set up the values for the shuffle vector fixup.
-      LHSMaxIdx = NumEltsOut / NumEltsIn;
-      SToVLHS = getSToVPermuted(SToVLHS, DAG, Subtarget);
-      if (SToVLHS.getValueType() != LHS.getValueType())
-        SToVLHS = DAG.getBitcast(LHS.getValueType(), SToVLHS);
-      LHS = SToVLHS;
+      LHS = generateSToVPermutedForVecShuffle(
+          LHSScalarSize, ShuffleEltWidth, LHSNumValidElts, LHSFirstElt,
+          LHSLastElt, LHS, SToVLHS, DAG, Subtarget);
     }
     if (SToVRHS) {
-      if (!IsLittleEndian && SToVRHS.getValueType().getScalarSizeInBits() >= 64)
+      int RHSScalarSize = SToVRHS.getValueType().getScalarSizeInBits();
+      if (!IsLittleEndian && RHSScalarSize >= 64)
         return Res;
-      RHSMinIdx = NumEltsOut;
-      RHSMaxIdx = NumEltsOut / NumEltsIn + RHSMinIdx;
-      SToVRHS = getSToVPermuted(SToVRHS, DAG, Subtarget);
-      if (SToVRHS.getValueType() != RHS.getValueType())
-        SToVRHS = DAG.getBitcast(RHS.getValueType(), SToVRHS);
-      RHS = SToVRHS;
+      RHS = generateSToVPermutedForVecShuffle(
+          RHSScalarSize, ShuffleEltWidth, RHSNumValidElts, RHSFirstElt,
+          RHSLastElt, RHS, SToVRHS, DAG, Subtarget);
     }
 
+    if (!isShuffleMaskInRange(ShuffV, HalfVec, LHSLastElt, RHSLastElt))
+      return Res;
+
     // Fix up the shuffle mask to reflect where the desired element actually is.
     // The minimum and maximum indices that correspond to element zero for both
     // the LHS and RHS are computed and will control which shuffle mask entries
     // are to be changed. For example, if the RHS is permuted, any shuffle mask
-    // entries in the range [RHSMinIdx,RHSMaxIdx) will be adjusted.
-    fixupShuffleMaskForPermutedSToV(ShuffV, LHSMaxIdx, RHSMinIdx, RHSMaxIdx,
-                                    HalfVec, ValidLaneWidth, Subtarget);
+    // entries in the range [RHSFirstElt,RHSLastElt] will be adjusted.
+    fixupShuffleMaskForPermutedSToV(
+        ShuffV, LHSFirstElt, LHSLastElt, RHSFirstElt, RHSLastElt, HalfVec,
----------------
amy-kwan wrote:

Although the LHSFirstElt and RHSFirstElt values do not change, I think it would be good to be explicit to mention them here so it's obvious to the reader of the code what values are needed when we need to fix up the shuffle mask (after generating the `SCALAR_TO_VECTOR_PERMUTED` node).

https://github.com/llvm/llvm-project/pull/80784