[Bug debug/78685] New: -Og generates too many "<optimized out>"s

[eggert at gnu dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78685

            Bug ID: 78685
           Summary: -Og generates too many "<optimized out>"s
           Product: gcc
           Version: 6.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eggert at gnu dot org
  Target Milestone: ---
              Host: x86-64

Created attachment 40253
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40253&action=edit
preprocessed C program illustrating -Og problem

Emacs developers are having trouble using -Og to debug Emacs, and so are still
using -O0; see, for example:

http://lists.gnu.org/archive/html/emacs-devel/2016-12/msg00199.html

I reproduced the problem and came up with a small program (attached) that
illustrates it. Here's a sample transcript on Fedora 24 x86-64, which uses gcc
(GCC) 6.2.1 20160916 (Red Hat 6.2.1-2):

$ gcc -Og -g3 Ogbug.i
$ gdb a.out
GNU gdb (GDB) Fedora 7.11.1-86.fc24
...
Reading symbols from a.out...done.
(gdb) b call_debugger
Breakpoint 1 at 0x4004d6: file Ogbug.i, line 6.
(gdb) r
Starting program: /home/eggert/junk/a.out 

Breakpoint 1, call_debugger (x=3) at Ogbug.i:6
6         v = x;
(gdb) bt
#0  call_debugger (x=3) at Ogbug.i:6
#1  0x0000000000400519 in apply_lambda (fun=1, args=2, count=<optimized out>)
    at Ogbug.i:14
#2  0x0000000000400547 in main (argc=<optimized out>, argv=<optimized out>)
    at Ogbug.i:22


It's hard to debug a program with all those "<optimized out>"s getting in the
way.