[llvm] [LLVM][VPlan] Pick more optimal initial value for VPBlend. (PR #104019)

[via llvm-commits]

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@@ -918,6 +918,16 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
     // value with the others blended into it.
 
     unsigned StartIndex = 0;
+    for (unsigned I = 0; I != Blend->getNumIncomingValues(); ++I) {
+      // If a value's mask is only used by the blend then is can be deadcoded.
+      // TODO: Find the most expensive mask that can be deadcoded.
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ayalz wrote:

All phi's of a block are converted to blends with the same edge masks, so looking for a mask with a single blend using it restricts this patch to single phi'd blocks only.

https://github.com/llvm/llvm-project/pull/104019