[llvm-commits] [llvm] r118440 - /llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp

[Dan Gohman]

Author: djg
Date: Mon Nov  8 14:26:19 2010
New Revision: 118440

URL: http://llvm.org/viewvc/llvm-project?rev=118440&view=rev
Log:
Re-introduce the MaxLookup limit to BasicAliasAnalysis'
pointsToConstantMemory code to guard against possible
compile time slowdowns.

Modified:
    llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp

Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=118440&r1=118439&r2=118440&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Mon Nov  8 14:26:19 2010
@@ -524,6 +524,7 @@
 BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
   assert(Visited.empty() && "Visited must be cleared after use!");
 
+  unsigned MaxLookup = 8;
   SmallVector<const Value *, 16> Worklist;
   Worklist.push_back(Loc.Ptr);
   do {
@@ -559,6 +560,11 @@
     // If all values incoming to a phi node point to local memory, then so does
     // the phi.
     if (const PHINode *PN = dyn_cast<PHINode>(V)) {
+      // Don't bother inspecting phi nodes with many operands.
+      if (PN->getNumIncomingValues() > MaxLookup) {
+        Visited.clear();
+        return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+      }
       for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
         Worklist.push_back(PN->getIncomingValue(i));
       continue;
@@ -568,10 +574,10 @@
     Visited.clear();
     return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
 
-  } while (!Worklist.empty());
+  } while (!Worklist.empty() && --MaxLookup);
 
   Visited.clear();
-  return true;
+  return Worklist.empty();
 }
 
 /// getModRefBehavior - Return the behavior when calling the given call site.