[llvm] [VPlan] Remove ExtractLastLane for plans with scalar VFs. (PR #171145)

[via llvm-commits]

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@@ -1385,12 +1385,16 @@ static void simplifyRecipe(VPSingleDefRecipe *Def, VPTypeAnalysis &TypeInfo) {
     return;
   }
 
-  // Look through ExtractLastLane (BuildVector ....).
-  if (match(Def, m_ExtractLastLane(m_BuildVector()))) {
-    auto *BuildVector = cast<VPInstruction>(Def->getOperand(0));
-    Def->replaceAllUsesWith(
-        BuildVector->getOperand(BuildVector->getNumOperands() - 1));
-    return;
+  // Look through ExtractLastLane.
+  if (match(Def, m_ExtractLastLane(m_VPValue(A)))) {
+    if (match(A, m_BuildVector())) {
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ayalz wrote:

Such BuildVector operands were visited and processed earlier by the code below folding them into Broadcast if all their operands are equal. Does that folding hold for VF=1 too; if so should such redundant Broadcasts be eliminated too? Worth looking for extracts from broadcast too/instead?

https://github.com/llvm/llvm-project/pull/171145