[llvm] [LLVM][VPlan] Keep all VPBlend masks until VPlan transformation. (PR #104015)

[David Sherwood via llvm-commits]

================
@@ -2048,19 +2048,23 @@ class VPBlendRecipe : public VPSingleDefRecipe {
 
   VP_CLASSOF_IMPL(VPDef::VPBlendSC)
 
+  /// A normalized blend is one that has an odd number of operands, whereby the
+  /// first operand does not have an associated mask.
+  bool isNormalized() const { return getNumOperands() % 2; }
+
   /// Return the number of incoming values, taking into account that the first
   /// incoming value has no mask.
   unsigned getNumIncomingValues() const { return (getNumOperands() + 1) / 2; }
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david-arm wrote:

This looks incorrect when the recipe is not normalised. Should it be

```
  unsigned getNumIncomingValues() const { return (getNumOperands() + isNormalized()) / 2; }
```

?

https://github.com/llvm/llvm-project/pull/104015