[PATCH] D33756: [RS4GC] Drop invalid metadata after pointers are relocated

[Anna Thomas via Phabricator via llvm-commits]

anna added inline comments.


================
Comment at: lib/Transforms/Scalar/RewriteStatepointsForGC.cpp:2351
+    // metadata that's invalid after RS4GC.
+    if (isa<LoadInst>(I) && I.getMetadata(LLVMContext::MD_invariant_load))
+      I.dropUnknownNonDebugMetadata(KnownIDs);
----------------
reames wrote:
> I think that a better factoring on this would be to factor out something from RemoveNonValidAttrAtIndex which works on a load, call it on a load, then add !invariant.load to that list.  This is not specific to invariant load.  Really, we'd just completely failed to think about loads in implementing this.
I don't think we can factor out anything from `RemoveNonValidAttrAtIndex`. We are trying to remove metadata and not attributes. Also, there is no way to specify something like `I.removeMetadata(invariant_load)`, and such a function should *not* be added in Instruction class. The reason being we need to keep auditing code for correctness to keep track of all new metadata that gets added to langref.  The `dropUnknownNonDebugMetadata(knownIDs)` works *correctly* without any changes even when new metadata gets added.

Also, `I.dropUnknownNonDebugMetadata` updates private members in Instruction once no metadata is left behind in that instruction. 

I can introduce a function like `DropInvalidMetadataOnInstruction` and call it on a load instruction. Does that work?




https://reviews.llvm.org/D33756