[llvm] [NFC][VPlan] Rename VPEVLBasedIVPHIRecipe to VPCurrentIterationPHIRecipe (PR #177114)

[Florian Hahn via llvm-commits]

================
@@ -3756,30 +3756,30 @@ class VPActiveLaneMaskPHIRecipe : public VPHeaderPHIRecipe {
 #endif
 };
 
-/// A recipe for generating the phi node for the current index of elements,
-/// adjusted in accordance with EVL value. It starts at the start value of the
-/// canonical induction and gets incremented by EVL in each iteration of the
-/// vector loop.
-class VPEVLBasedIVPHIRecipe : public VPHeaderPHIRecipe {
+/// A recipe for generating the phi node tracking the current scalar iteration
+/// index. It starts at the start value of the canonical induction and gets
+/// incremented by the number of scalar iterations processed per vector loop
+/// iteration.
----------------
fhahn wrote:

```suggestion
/// incremented by the number of scalar iterations processed by the current vector loop
/// iteration. The increment does not have to be loop invariant.
```

to clarify that this can change between loop iterations

https://github.com/llvm/llvm-project/pull/177114