[PATCH] D73706: [NFC][SCEV] SCEVExpander::isHighCostExpansionHelper(): check that we processed expression first

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: reames, mkazantsev, wmi, sanjoy, atrick, igor-laevsky.
lebedev.ri added a project: LLVM.
Herald added a subscriber: hiraditya.
lebedev.ri added a parent revision: D73705: [NFC][SCEV] Piping to pass new SCEVCheapExpansionBudget option into SCEVExpander::isHighCostExpansionHelper().

As far as i can tell this is still NFC.
Initially in rL146438 <https://reviews.llvm.org/rL146438> it was added at the top of the function,
later rL238507 <https://reviews.llvm.org/rL238507> dethroned it, and rL244474 <https://reviews.llvm.org/rL244474> did it again.

I'm not sure if we have already checked the cost of this expansion, we should be doing that again.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73706

Files:
  llvm/lib/Analysis/ScalarEvolutionExpander.cpp


Index: llvm/lib/Analysis/ScalarEvolutionExpander.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -2138,6 +2138,10 @@
 bool SCEVExpander::isHighCostExpansionHelper(
     const SCEV *S, Loop *L, const Instruction *At, int BudgetRemaining,
     const TargetTransformInfo *TTI, SmallPtrSetImpl<const SCEV *> &Processed) {
+  // Was the cost of expansion of this expression already accounted for?
+  if (!Processed.insert(S).second)
+    return false; // We have already accounted for this expression.
+
   // If we can find an existing value for this scev available at the point "At"
   // then consider the expression cheap.
   if (At && getRelatedExistingExpansion(S, At, L))
@@ -2159,8 +2163,6 @@
                                      L, At, BudgetRemaining, TTI, Processed);
   }
 
-  if (!Processed.insert(S).second)
-    return false;
 
   if (auto *UDivExpr = dyn_cast<SCEVUDivExpr>(S)) {
     // If the divisor is a power of two and the SCEV type fits in a native


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D73706.241436.patch
Type: text/x-patch
Size: 1095 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200130/73c9723a/attachment.bin>