[all-commits] [llvm/llvm-project] 10cc3a: [MS-ABI] skip generate comdat for vftable defined ...

[jyu2-git via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 10cc3a8556a8ff9557890c96de162cb2c09669e2
      https://github.com/llvm/llvm-project/commit/10cc3a8556a8ff9557890c96de162cb2c09669e2
  Author: jyu2-git <jennifer.yu at intel.com>
  Date:   2023-11-15 (Wed, 15 Nov 2023)

  Changed paths:
    M clang/lib/CodeGen/MicrosoftCXXABI.cpp
    A clang/test/CodeGenCXX/ms-local-vft-alias-comdat.cpp
    M clang/test/CodeGenCXX/type-metadata.cpp

  Log Message:
  -----------
  [MS-ABI] skip generate comdat for vftable defined with internal alias. (#71748)

We got a error:
`LLVM ERROR: Associative COMDAT symbol '??_7?$T at V<lambda_0>@@@@6B@' is
not a key for its COMDAT`

Current we create internal alias for vftable when lambd is used.
For the test, IR generate:
```
 $"??_7?$T at V<lambda_0>@@$0A@@@6b@" = comdat any

@0 = private unnamed_addr constant { [2 x ptr] } { [2 x ptr] [ptr @"??_R4?$T at V<lambda_0>@@$0A@@@6b@", ptr @"?c at b@@UEAAXXZ"] }, comdat($"??_7?$T at V<lambda_0>@@$0A@@@6b@")

@"??_7?$T at V<lambda_0>@@$0A@@@6b@" = internal unnamed_addr alias ptr, getelementptr inbounds ({ [2 x ptr] }, ptr @0, i32 0, i32 0, i32 1)
```

According LLVM language reference manual section on COMDATs:
There are some restrictions on the properties of the global object. It,
or an alias to it, must have the same name as the COMDAT group when
targeting COFF. The contents and size of this object may be used during
link-time to determine which COMDAT groups get selected depending on the
selection kind. Because the name of the object must match the name of
the
COMDAT group, the linkage of the global object must not be local; local
symbols can get renamed if a collision occurs in the symbol table.

So one way to fix this is to not create comdat for the alias.

@0 = private unnamed_addr constant { [2 x ptr] } { [2 x ptr] [ptr
@"??_R4?$T at V<lambda_0>@@@@6B@", ptr @"?c@?$T at V<lambda_0>@@@@UEAAXXZ"] }