[llvm] [VPlan] Replace VPRecipeOrVPValue with VP2VP recipe simplification. (PR #76090)

[via llvm-commits]

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@@ -806,6 +806,38 @@ static unsigned getOpcodeForRecipe(VPRecipeBase &R) {
 
 /// Try to simplify recipe \p R.
 static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
+  // Try to remove redundant blend recipes.
+  if (auto *Blend = dyn_cast<VPBlendRecipe>(&R)) {
+    if (Blend->getNumIncomingValues() == 1) {
+      Blend->replaceAllUsesWith(Blend->getIncomingValue(0));
+      Blend->eraseFromParent();
+      return;
+    }
+
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ayalz wrote:

```suggestion
```

Single incoming is a corner case of all incomings being equal, can be left to be handled below.
Wonder if/where it actually occurs - lcssa/header phi's should remain intact.

All incomings being equal should be optimized at the scalar phi level - when such an initial VPlan will be made available.


https://github.com/llvm/llvm-project/pull/76090