[llvm-bugs] [Bug 35994] New: Duplicate vtables generated

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35994

            Bug ID: 35994
           Summary: Duplicate vtables generated
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: COFF
          Assignee: unassignedbugs at nondot.org
          Reporter: brucedawson at chromium.org
                CC: llvm-bugs at lists.llvm.org

Created attachment 19699
  --> https://bugs.llvm.org/attachment.cgi?id=19699&action=edit
A report of all vftable symbols that waste more than 31 bytes

When running my ShowGlobals tool on the latest Chromium canary I noticed that
many v-tables were showing up multiple times. The attached file is a report for
chrome_child.dll.pdb. The first column is the number of excess copies of the
`vftable' symbols - a value of 1 means there is 1 extra copy, or 2 total.

The second column is the space wasted, in bytes. It is simply the size of the
v-table times the first column. The third column is the symbol name.

Possibly related to https://bugs.llvm.org/show_bug.cgi?id=31220?

This duplication was not seen when building with VC++. The total waste is not
huge but it seemed worth mentioning. It's not clear whether this is a problem
with the compiler or linker.

Objects that waste less than 32 bytes are not reported on (IIRC).

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