dblaikie added inline comments.
================
Comment at: lib/CodeGen/CGDebugInfo.cpp:812-814
+ // CodeView types with C++ mangling need a type identifier.
+ if (CGM.getCodeGenOpts().EmitCodeView)
+ return true;
----------------
Just came across this code today - it's /probably/ a problem for LTO. LLVM IR
linking depends on the identifier to determine if two structs are the same for
linkage purposes - so if an identifier is added for a non-linkage (local/not
externally visible) type, LLVM will consider them to be the same even though
they're unrelated:
```
namespace { struct t1 { int i; int j; }; }
t1 v1;
void *v3 = &v1;
```
```
namespace { struct t1 { int i; }; }
t1 v1;
void *v2 = &v1;
```
```
$ clang++-tot -emit-llvm -S a.cpp b.cpp -g -gcodeview &&
~/dev/llvm/build/default/bin/llvm-link -o ab.bc a.ll b.ll &&
~/dev/llvm/build/default/bin/llvm-dis ab.bc && cat ab.ll | grep "\"t1\""
!8 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t1", scope:
!9, file: !3, line: 1, size: 64, flags: DIFlagTypePassByValue, elements: !10,
identifier: "_ZTSN12_GLOBAL__N_12t1E")
$ clang++-tot -emit-llvm -S a.cpp b.cpp -g &&
~/dev/llvm/build/default/bin/llvm-link -o ab.bc a.ll b.ll &&
~/dev/llvm/build/default/bin/llvm-dis ab.bc && cat ab.ll | grep "\"t1\""
!8 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t1", scope:
!9, file: !3, line: 1, size: 64, flags: DIFlagTypePassByValue, elements: !10)
!21 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "t1", scope:
!9, file: !17, line: 1, size: 32, flags: DIFlagTypePassByValue, elements: !22)
```
So in linking, now both `a.cpp` and `b.cpp` refer to a single `t1` type (in
this case, it looks like the first one - the 64 bit wide one).
If CodeView actually can't represent these two distinct types with the same
name in the same object file, so be it? But this looks like it's likely to
cause problems for consumers/users.
Repository:
rC Clang
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D45438/new/
https://reviews.llvm.org/D45438
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