[PATCH] D12080: [PM/AA] Rebuild LLVM's alias analysis infrastructure in a way compatible with the new pass manager, and no longer relying on analysis groups.

[Chandler Carruth via llvm-commits]

chandlerc added inline comments.

================
Comment at: lib/Analysis/BasicAliasAnalysis.cpp:603
@@ +602,3 @@
+      AliasResult AR =
+          AAR ? AAR->alias(MemoryLocation(*CI), MemoryLocation(Object))
+              : alias(MemoryLocation(*CI), MemoryLocation(Object));
----------------
hfinkel wrote:
> That comment is good, but let me clarify something: Is this the general pattern necessary for recursion in AA? Specifically, if there is an aggregation object, then recurse through the aggregation object so the entire chain participates, otherwise, just recurse directly? If this is the general pattern, then we should add it as a utility function and not repeat it everywhere it might be necessary. In short, what to do when one AA can reduce an aliasing query to another one on some underlying pointers should be something that is clear within the interface.
> 
Any suggestions about *how* to factor this out? I tried to come up with a way, and it involved horrible templates and pointers-to-members or std::bind craziness. I'll try again myself...

================
Comment at: lib/Analysis/BasicAliasAnalysis.cpp:1237-1238
@@ -1279,4 +1236,4 @@
   AliasResult Result =
-      AliasAnalysis::alias(MemoryLocation(V1, V1Size, V1AAInfo),
-                           MemoryLocation(V2, V2Size, V2AAInfo));
+      AAResultBase::alias(MemoryLocation(V1, V1Size, V1AAInfo),
+                          MemoryLocation(V2, V2Size, V2AAInfo));
   return AliasCache[Locs] = Result;
----------------
I really don't know... The old code had different fallback strategies and it wasn't always clear to me whether they would fully recurse or partially recurse, etc.

In particular, does this inf-loop? Anyways, I'll try to make this more rigorous. I need to find out if it would infloop and the old code was trying to delegate to the *other* AAs by doing this, and if so, have it return MayAlias.


http://reviews.llvm.org/D12080