[llvm] [VPlan] - Generalize dead cycle removal in removeDeadRecipes. (PR #213632)

[Pawan Nirpal via llvm-commits]

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@@ -687,6 +687,32 @@ static void removeRedundantInductionCasts(VPlan &Plan) {
   }
 }
 
+/// If R is a phi-like recipe starting a dead cycle of recipes, erase all
+/// reachable recipes of the dead cycle.
+static void tryToRemoveDeadCycle(VPRecipeBase *R) {
+  auto *PhiR = dyn_cast<VPSingleDefRecipe>(R);
+  if (!PhiR || !isa<VPPhi, VPReductionPHIRecipe>(R))
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pawan-nirpal-031 wrote:

> we could support un-truncated inductions here as well, truncated ones should also be fine, but would need materializing the truncate in the preheader. But does not need to be in the patch.

Sure @fhahn I'll restrict this patch for now, and plan a following patch to extend support to truncated/un-truncated inductions. 

https://github.com/llvm/llvm-project/pull/213632