[llvm] [VPlan] Use VPInstructionWithType for uniform casts. (PR #140623)

[via llvm-commits]

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@@ -919,6 +919,9 @@ class VPInstruction : public VPRecipeWithIRFlags,
                       public VPUnrollPartAccessor<1> {
   friend class VPlanSlp;
 
+  /// True if the VPInstruction produces a single scalar value.
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ayalz wrote:

And false if it doesn't, i.e., if the VPInstruction produces more than one scalar value, or none - produces a vector instead or produces no value at all as in branches (for stores we consider the stored value as being "produced"?)
Holds for all VPValues of VPlan0?

https://github.com/llvm/llvm-project/pull/140623