[cfe-dev] Compiling with both -flto and -g -- is it supposed to work ?

[Philippe Blain via cfe-dev]

Hello, 

I'm wondering if compiling with both `-flto` and `-g` is supported. I could not find any open bug on the bugzilla and the documentation does not mention it should or should not work.

When I do that (I also use `-flto` at the link step), and open the generated executable in GDB (tried both 8.3.1 and 9.2), I get the following:
```
$ gdb --args python testing/process_to_debug.py 
GNU gdb (GDB) 8.3.1
Reading symbols from <executable>...

warning: `/tmp/lto.o': can't open to read symbols: No such file or directory.
(No debugging symbols found in <executable>)
(gdb) r
Starting program: /Users/Philippe/Logiciels/miniconda3/envs/gdb/bin/python testing/process_to_debug.py
[New Thread 0x1103 of process 75303]
warning: `/tmp/lto.o': can't open to read symbols: No such file or directory.
```

I get set breakpoints at symbol names, but can't `list` or see function arguments...

This is on macOS 10.11.6, using the pre-compiled clang from https://releases.llvm.org/download.html:
$ clang --version
clang version 9.0.0 (git://github.com/llvm/llvm-project.git 0399d5a9682b3cef71c653373e38890c63c4c365)

and the system linker (I do use the above clang as the driver for the link step) :
$ ld -v
@(#)PROGRAM:ld  PROJECT:ld64-274.2
configured to support archs: armv6 armv7 armv7s arm64 i386 x86_64 x86_64h armv6m armv7k armv7m armv7em (tvOS)
LTO support using: LLVM version 8.0.0, (clang-800.0.42.1)
TAPI support using: Apple TAPI version 1.30

For reference I tried with <executable> being Git and Python..
I also tried debugging with the system LLDB (lldb-360.1.70) and the latter does not complain when loading the executable, but I get pretty much the same behaviour, nothing more than function names are available...

Also, dwarfdump outputs:
$ dwarfdump git
----------------------------------------------------------------------
 File: git (x86_64)
----------------------------------------------------------------------
.debug_info contents:
< EMPTY >

Is this normal behaviour ?

Thanks,
Philippe.
P.S.: this is my first time posting here so don't hesitate if more information is needed.