[llvm] [VPlan] Simplify vp.merge true, (or x, y), x -> vp.merge y, true, x (PR #135017)

[Florian Hahn via llvm-commits]

================
@@ -439,6 +457,104 @@ m_DerivedIV(const Op0_t &Op0, const Op1_t &Op1, const Op2_t &Op2) {
   return VPDerivedIV_match<Op0_t, Op1_t, Op2_t>({Op0, Op1, Op2});
 }
 
+template <typename Opnd_t> struct Argument_match {
+  unsigned OpI;
+  Opnd_t Val;
+
+  Argument_match(unsigned OpIdx, const Opnd_t &V) : OpI(OpIdx), Val(V) {}
+
+  template <typename OpTy> bool match(OpTy *V) const {
+    if (const auto *R = dyn_cast<VPWidenIntrinsicRecipe>(V))
+      return Val.match(R->getOperand(OpI));
+    if (const auto *R = dyn_cast<VPWidenCallRecipe>(V))
+      return Val.match(R->getOperand(OpI));
+    if (const auto *R = dyn_cast<VPReplicateRecipe>(V))
+      if (isa<CallInst>(R->getUnderlyingInstr()))
+        return Val.match(R->getOperand(OpI + 1));
+    return false;
+  }
+};
+
+/// Match an argument.
----------------
fhahn wrote:

```suggestion
/// Match call argument.
```
to clarify as there's no `Argument` class used in VPlan.

https://github.com/llvm/llvm-project/pull/135017