[Bug debug/68836] New: GCC can't properly emit debug info for function arguments in a back-trace when using -Og

["marxin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68836

            Bug ID: 68836
           Summary: GCC can't properly emit debug info for function
                    arguments in a back-trace when using -Og
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
  Target Milestone: ---

The original problem was reported by perf guys who have been using -Og as their
default
debugging option. However, it's quite common that back-traces of function
arguments are optimized out:

#0  0x00000000004b490f in parse_events__scan_string (yystr=yystr@entry=0x0,
yyscanner=0x1916be0) at util/parse-events-flex.c:3353
#1  0x000000000048fe6f in parse_events__scanner (str=0x0,
data=data@entry=0x7fffffffdac0, start_token=start_token@entry=258)
    at util/parse-events.c:1356
#2  0x0000000000491775 in parse_events (evlist=evlist@entry=0x1917c90,
str=<optimized out>, err=err@entry=0x0) at util/parse-events.c:1401
#3  0x0000000000468bf6 in __perf_evsel__name_array_test (names=0x872c00
<perf_evsel.sw_names>, nr_names=nr_names@entry=11)
    at tests/evsel-roundtrip-name.c:74
#4  0x0000000000468f13 in test__perf_evsel__roundtrip_name_test
(subtest=<optimized out>) at tests/evsel-roundtrip-name.c:106
#5  0x000000000045a2c8 in run_test (test=test@entry=0x86fe50
<generic_tests+400>, subtest=subtest@entry=-1) at tests/builtin-test.c:241
#6  0x000000000045a3a1 in test_and_print (t=t@entry=0x86fe50
<generic_tests+400>, force_skip=force_skip@entry=false,
    subtest=subtest@entry=-1) at tests/builtin-test.c:268
#7  0x000000000045a5cd in __cmd_test (argc=argc@entry=1,
argv=argv@entry=0x7fffffffe200, skiplist=0x0) at tests/builtin-test.c:324
#8  0x000000000045a8a9 in cmd_test (argc=1, argv=0x7fffffffe200,
prefix=<optimized out>) at tests/builtin-test.c:416
#9  0x00000000004784a9 in run_builtin (p=p@entry=0x871e18 <commands+504>,
argc=argc@entry=2, argv=argv@entry=0x7fffffffe200) at perf.c:387
#10 0x00000000004786a4 in handle_internal_command (argc=2, argv=0x7fffffffe200)
at perf.c:448
#11 0x0000000000478710 in run_argv (argcp=argcp@entry=0x7fffffffe06c,
argv=argv@entry=0x7fffffffe060) at perf.c:492
#12 0x0000000000478981 in main (argc=2, argv=0x7fffffffe200) at perf.c:609