Commits on Aug 15, 2024

1. [FIRRTL] Update LowerClasses to alter what PathInfo stores. …

   PathInfo stores a pointer to an Operation, which was problematic
   because that Operation may be deleted in updateInstanceInModule. The
   test case added in this patch would lead to a use-after-free.
   
   This pointer was only really used for a few things, which can be
   handled differently to avoid needing to consider Operation lifetimes.
   
   One use was the operator bool implementation, to check if a PathInfo is
   empty. In the one place this was used, an equivalent check is to query
   the PathInfoTable, and check if the key was not in the table.
   
   Another use was adding the Operation's location in error messages and
   notes. We can safely store a Location directly for these messages.
   
   The final use was to do an isa check while determining the target
   kind. This is where the use in the use-after-free would manifest. For
   this, we do the isa check early, and store the result in a bool.
   
   In summary, we are able to simplify the data in PathInfo in order to
   avoid hanging on to an Operation pointer and needing to worry about
   its lifetime.

   

   mikeurbach committed Aug 15, 2024
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