Initialize BasicAA's AliasCache to set it to use fewer buckets by

default, since it usually has very few elements. This speeds up
alias queries in many cases, because AliasCache.clear() doesn't
have to visit as many buckets.

llvm-svn: 132862

llvm/lib/Analysis/BasicAliasAnalysis.cpp

@@ -451,7 +451,13 @@ namespace {
   /// BasicAliasAnalysis - This is the primary alias analysis implementation.
   struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
     static char ID; // Class identification, replacement for typeinfo
-    BasicAliasAnalysis() : ImmutablePass(ID) {
+    BasicAliasAnalysis() : ImmutablePass(ID),
+                           // AliasCache rarely has more than 1 or 2 elements,
+                           // so start it off fairly small so that clear()
+                           // doesn't have to tromp through 64 (the default)
+                           // elements on each alias query. This really wants
+                           // something like a SmallDenseMap.
+                           AliasCache(8) {
       initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
     }