[llvm-commits] [llvm] r146438 - /llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp

[Andrew Trick]

Author: atrick
Date: Mon Dec 12 16:46:16 2011
New Revision: 146438

URL: http://llvm.org/viewvc/llvm-project?rev=146438&view=rev
Log:
Indvars: guard against exponential behavior in isHighCostExpansion.

This should always be done as a matter of principal. I don't have a
case that exposes the problem. I just noticed this recently while
scanning the code and realized I meant to fix it long ago.

Modified:
    llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=146438&r1=146437&r2=146438&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Mon Dec 12 16:46:16 2011
@@ -1238,7 +1238,11 @@
 /// BackedgeTakenInfo. If these expressions have not been reduced, then
 /// expanding them may incur additional cost (albeit in the loop preheader).
 static bool isHighCostExpansion(const SCEV *S, BranchInst *BI,
+                                SmallPtrSet<const SCEV*, 8> &Processed,
                                 ScalarEvolution *SE) {
+  if (!Processed.insert(S))
+    return false;
+
   // If the backedge-taken count is a UDiv, it's very likely a UDiv that
   // ScalarEvolution's HowFarToZero or HowManyLessThans produced to compute a
   // precise expression, rather than a UDiv from the user's code. If we can't
@@ -1266,7 +1270,7 @@
   if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
     for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
          I != E; ++I) {
-      if (isHighCostExpansion(*I, BI, SE))
+      if (isHighCostExpansion(*I, BI, Processed, SE))
         return true;
     }
     return false;
@@ -1309,7 +1313,8 @@
   if (!BI)
     return false;
 
-  if (isHighCostExpansion(BackedgeTakenCount, BI, SE))
+  SmallPtrSet<const SCEV*, 8> Processed;
+  if (isHighCostExpansion(BackedgeTakenCount, BI, Processed, SE))
     return false;
 
   return true;