[llvm-branch-commits] [llvm] [LoopVectorize] Support vectorization of compressing patterns in VPlan (PR #140723)

[Luke Lau via llvm-branch-commits]

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@@ -8430,6 +8479,46 @@ VPlanPtr LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(
   // bring the VPlan to its final state.
   // ---------------------------------------------------------------------------
 
+  // Adjust the recipes for any monotonic phis.
+  for (VPRecipeBase &R : HeaderVPBB->phis()) {
+    auto *MonotonicPhi = dyn_cast<VPMonotonicPHIRecipe>(&R);
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lukel97 wrote:

If you use a regular VPInstruction::PHI instead of VPMonotonicPHIRecipe and set the underlying value to the monotonic phi, could you avoid the need for an extra recipe?

Would you be able to detect the monotonic phis by just calling `Legal->getMonotonicPHIs().find(Phi->getUnderlyingValue())`?

https://github.com/llvm/llvm-project/pull/140723