[AliasSetTracker] More precise AAInfo intersection check

[nikic]

Summary

The code currently checks whether the intersection has one of TBAA, Scope or NoAlias unset -- however, those might have already been unset in the first place, in which case we will unnecessarily report a change. Instead, compare the intersection result to the original AAInfo.

This makes for a 0.5% geomean compile-time saving: https://llvm-compile-time-tracker.com/compare.php?from=0b39d2d75275b80994dac06b7ad05031cbd09393&to=7e6dc7d267393489b12e4884641f411d375d000e&stat=instructions

The current form of the check was introduced in https://github.com/llvm/llvm-project/commit/35548e80d67dd0d6e61c489432cfb1dafe0ddb65, which is how I ran into this.

[asbirlea]

LGTM, thank you!

llvm/include/llvm/Analysis/AliasSetTracker.h

bool updateSizeAndAAInfo(LocationSize NewSize, const AAMDNodes &NewAAInfo) {
         SizeChanged = OldSize != Size;
       }
 
       if (AAInfo == DenseMapInfo<AAMDNodes>::getEmptyKey())
         // We don't have a AAInfo yet. Set it to NewAAInfo.
         AAInfo = NewAAInfo;
       else {
         AAMDNodes Intersection(AAInfo.intersect(NewAAInfo));
-        if (!Intersection.TBAA || !Intersection.Scope ||
-            !Intersection.NoAlias) {
-          // NewAAInfo conflicts with AAInfo.
-          AAInfo = DenseMapInfo<AAMDNodes>::getTombstoneKey();
-          SizeChanged = true;
-        }
+        SizeChanged |= Intersection != AAInfo;
         AAInfo = Intersection;
       }
       return SizeChanged;
     }
 
     LocationSize getSize() const {
       assert(isSizeSet() && "Getting an unset size!");
       return Size;