Lambda function names generated by Clang does not conform to ABI

[lxfind]

Bugzilla Link	50209
Version	trunk
OS	Linux
CC	@dwblaikie,@DougGregor,@Dushistov,@efriedma-quic,@urnathan,@zygoloid,@tstellar

Extended Description

When compiling lambda functions, the generated function
names use different conventions than GCC.
Example: https://godbolt.org/z/5qvqKqEe6
The lambda in Clang is named _Z3barIZ3foovE3$_0EvT_, while the one
in GCC is named _Z3barIZ3foovEUlvE_EvT_. Their demangled names are
also different (void bar<foo()::$_0>(foo()::$_0) vs void bar<foo()::{lambda()#1}>(foo()::{lambda()#1})).

Discussions in clang-dev: https://lists.llvm.org/pipermail/cfe-dev/2021-May/068080.html

[lxfind]

A potentially relevant bug: #49309

[efriedma-quic]

We have code to perform the correct mangling for externally visible symbols. For example:

inline int f(int x) {
return [=]{static int z; z += x; return z; }();
}
void g() { f(3); }

The ABI rules are only relevant for externally visible symbols, though; we can name internal symbols however we want.

There might be some argument that we should change the mangling to help debuggers/profilers/etc., if the current mangling produces bad results. But that's more of a quality of implementation thing.

[llvmbot]

changed the description

[llvmbot]

changed the description

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Xun Li (lxfind)

| | | | --- | --- | | Bugzilla Link | [50209](https://llvm.org/bz50209) | | Version | trunk | | OS | Linux | | CC | @dwblaikie,@DougGregor,@dushistov,@efriedma-quic,@urnathan,@zygoloid,@tstellar |

Extended Description

When compiling lambda functions, the generated function
names use different conventions than GCC.
Example: https://godbolt.org/z/5qvqKqEe6
The lambda in Clang is named _Z3barIZ3foovE3$_0EvT_, while the one
in GCC is named _Z3barIZ3foovEUlvE_EvT_. Their demangled names are
also different (void bar<foo()::$_0>(foo()::$_0) vs void bar&lt;foo()::{lambda()#<!-- -->1}&gt;(foo()::{lambda()#<!-- -->1})).

Discussions in clang-dev: https://lists.llvm.org/pipermail/cfe-dev/2021-May/068080.html

[Michael137]

related discussions #73521