[llvm-bugs] [Bug 45950] New: LLD generates duplicate .pdata chunks

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45950

            Bug ID: 45950
           Summary: LLD generates duplicate .pdata chunks
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: COFF
          Assignee: unassignedbugs at nondot.org
          Reporter: alexandre.ganea at ubisoft.com
                CC: llvm-bugs at lists.llvm.org, peter at pcc.me.uk,
                    rnk at google.com

We stumped on a case where LLD generates two identical RUNTIME_FUNCTION for the
same function, but with different UNWIND_INFO. This looks like an error, for
the same .OBJs, link.exe does not generate duplicates.

Function Table

           Begin    End      Info      Function Name

0049D0DC 0554E9D0 0554E9F7 06ACBCE8
   Unwind version: 1
   Unwind flags: EHANDLER UHANDLER
   Size of prologue: 0x0A
   Count of codes: 2
   Unwind codes:
     0A: ALLOC_SMALL, size=0x30
     06: PUSH_NONVOL, register=rbp
   Handler: 05503340 
0049D0E8 0554E9D0 0554E9F7 06ACB0E8
   Unwind version: 1
   Unwind flags: EHANDLER UHANDLER
   Size of prologue: 0x0A
   Count of codes: 2
   Unwind codes:
     0A: ALLOC_SMALL, size=0x30
     06: PUSH_NONVOL, register=rbp
   Handler: 05503340

Here, we get two RUNTIME_FUNCTION for function 0554E9D0, but two different
Info/UNWIND_INFO.

Interestingly, for the same inputs, we get a different number of entries
between different linkers:
   VS2019 16.5.4 link.exe : Function Table (316955)
   LLD 8.0:                 Function Table (316888)
   LLD 10.0:                Function Table (316959)

Any idea of what could be going on here? I was under the impression that we
need more than xxHash64 folding for .pdata chunks? Maybe a specific step after
ICF? I will dig next week.

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