[llvm] [LLVM][SelectionDAG] Ensure Constant[FP]SDnode only store references to scalar Constant{Int,FP}. (PR #111005)

[Paul Walker via llvm-commits]

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@@ -1656,6 +1656,11 @@ SDValue SelectionDAG::getConstant(const ConstantInt &Val, const SDLoc &DL,
   EVT EltVT = VT.getScalarType();
   const ConstantInt *Elt = &Val;
 
+  // Vector splats are explicit within the DAG, with ConstantSDNode holding the
+  // to be splatted scalar ConstantInt.
+  if (isa<VectorType>(Elt->getType()))
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paulwalker-arm wrote:

They don't have to match. In most cases `Val` will be the scalar you want to splat.  The new use case is when SelectionDAGBuilder passes in the new style ConstantInt which can have a vector result type when `use-constant-int-for-scalable-vector-splat` is enabled.

https://github.com/llvm/llvm-project/pull/111005