[llvm] [VPlan] Optimize FindLast of (binop %IV, live-in) by sinking. (PR #183911)

[Florian Hahn via llvm-commits]

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@@ -5786,16 +5853,37 @@ void VPlanTransforms::optimizeFindIVReductions(VPlan &Plan,
         BackedgeVal,
         match_fn(m_VPInstruction<VPInstruction::ComputeReductionResult>())));
 
+    // If IV is an expression to sink, create a new select that tracks the
+    // underlying IV directly and update the backedge value.
+    auto *OrigSelectR = FindLastSelect->getDefiningRecipe();
+    if (SinkExpressionIV) {
+      VPBuilder LoopBuilder(OrigSelectR);
+      auto DL = OrigSelectR->getDebugLoc();
+      VPValue *Cond = OrigSelectR->getOperand(0);
+      if (OrigSelectR->getOperand(1) == PhiR)
+        FindLastSelect =
+            LoopBuilder.createSelect(Cond, PhiR, SinkExpressionIV, DL);
+      else
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fhahn wrote:

added thanks

https://github.com/llvm/llvm-project/pull/183911