[PATCH] D99682: [SelectionDAG] Teach SelectionDAG::FoldConstantArithmetic to handle SPLAT_VECTOR

[David Sherwood via Phabricator via llvm-commits]

david-arm added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:5125
+  // SPLAT_VECTOR or UNDEF are present?
+  unsigned NumOps = VT.isScalableVector() ? 1 : VT.getVectorNumElements();
   for (unsigned I = 0; I != NumOps; ++I) {
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I wonder if it makes more sense to only set NumOps to VT.getVectorNumElements() if at least one opcode is BUILD_VECTOR. Then you can have an assert that for scalable vectors neither of the opcodes is BUILD_VECTOR.


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Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:5167
 
+  if (VT.isScalableVector()) {
+    assert(Outputs.size() == 1 && "Vector size mismatch!");
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This is just a suggestion, but instead of checking for scalable vectors, if you change NumOps above to be always be 1 if no BUILD_VECTORs are involved, then maybe you could write:

  if (Outputs.size() == 1) {
    // Must be a combination of either SPLAT_VECTOR or UNDEF.
    return getSplatVector(VT, SDLoc(), Outputs[0]);
  }

However, I'm not sure about the case when both inputs are UNDEF and maybe still want to return UNDEF?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D99682/new/

https://reviews.llvm.org/D99682