[PATCH] D12064: [GMR] isNonEscapingGlobalNoAlias() should look through Bitcasts/GEPs when looking at loads.

[Chandler Carruth via llvm-commits]

chandlerc added inline comments.

================
Comment at: lib/Analysis/IPA/GlobalsModRef.cpp:654
@@ -653,3 +653,3 @@
       // that the global is non-escaping, so no alias.
-      if (isa<GlobalValue>(LI->getPointerOperand()))
+      if (isa<GlobalValue>(GetUnderlyingObject(LI->getPointerOperand(), *DL)))
         continue;
----------------
hfinkel wrote:
> It seems like we could make this more general is two ways:
> 
>  1. Call GetUnderlyingObjects, and checking that all of the results are GlobalValues
> 
>  2. Also checking that the underlying objects are not arguments or call/invoke return values.
> 
> If I'm reading this code correctly, one possible way of handling this, is just to do this:
> 
>   push.Inputs(LI->getPointerOperand());
>   continue;
> 
> which seems to accomplish both things, and keeps an integrated Depth constraint.
> 
You're saying a pointer loaded from an escaping pointer is itself escaping?

I think I agree, but it makes this surprisingly more powerful. This will chase a chain of loads until it hits control flow or a known underlying object. Nifty, but maybe surprising.

However, unless I'm mistaken, we still need to call GetUnderlyingObject? The worklist doesn't do that.

I'm a bit scared about using GetUnderlyingObjects making this significantly more slow...


http://reviews.llvm.org/D12064