I tested on the current master:

git clean -fdx
./configure --with-lto --enable-optimizations
sed -i -e 's/^PROFILE_TASK=.*/PROFILE_TASK=-c pass/' Makefile
make 2>&1|tee log

Python is compiled twice:

* (1) gcc -DNDEBUG -g -O3 -flto -fprofile-generate (...)
* (2) gcc -DNDEBUG -g -O3 -flto -fprofile-use (...)

I see -g in both compilation steps.

It seems like debug symbols are still here:

vstinner@apu$ file ./python
./python: ELF 64-bit LSB executable, x86-64, (...), with debug_info, not stripped

But I confirm that test_gdb fails when using LTO+PGO.

gdb seems to be to read any C function argument:

$ gdb -args  ./python Lib/test/gdb_sample.py
(gdb) b builtin_id
(gdb) run
Breakpoint 1, 0x0000000000518da0 in builtin_id ()
(gdb) py-bt
Traceback (most recent call first):
  (unable to read python frame information)
  (unable to read python frame information)
  (unable to read python frame information)
  (unable to read python frame information)