[PATCH] D138412: [IndVarSimplify] Lift limitations on IV being a Phi for turn-to-invariant

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/SimplifyIndVar.cpp:224-229
+  if (Rewriter.isHighCostExpansion(InvariantLHS, L, SCEVCheapExpansionBudget,
+                                   TTI, PHTerm))
     return false;
-
+  if (Rewriter.isHighCostExpansion(InvariantRHS, L, SCEVCheapExpansionBudget,
+                                   TTI, PHTerm))
+    return false;
----------------
lebedev.ri wrote:
> I guess this is slightly broken, if rhs is constant but lhs needs 2x the `SCEVCheapExpansionBudget`,
> we'd still want to expand. (Well, or they both in total should fit into `SCEVCheapExpansionBudget`).
> But that is a separate issue.
We can improve `isHighCostExpansion` to take several SCEVs and compute at once, I'll see how hard it is to do it.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D138412/new/

https://reviews.llvm.org/D138412