[Bug debug/82010] New: Inspecting a function parameter of "vec *&path" from gdb yields nonsense.

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82010

            Bug ID: 82010
           Summary: Inspecting a function parameter of "vec<basic_block,
                    va_gc> *&path" from gdb yields nonsense.
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: aldyh at gcc dot gnu.org
  Target Milestone: ---

While debugging cc1, a function parameter of "vec<...> *&path" yields
garbabge when printing it from gdb:

(gdb) print path
$1 = Python Exception <class 'gdb.error'> Cannot convert value to long.:

whereas if you print the vector from the caller, gdb can see inside
the vector of basic blocks just fine:

(gdb) up
(gdb) print bb_path
$2 = 0x7fb8fca77000 = {<basic_block 0x7fb8fc93d270 (2)>}

Detailed steps follow:

$ cat a.c
void foo(int i)
{
  extern void bar ();
  if (i > 5)
    bar();
}

$ gdb cc1
GNU gdb (GDB) Fedora 8.0-22.fc26
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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and "show warranty" for details.
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Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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For help, type "help".
Type "apropos word" to search for commands related to "word"...
Demangling of encoded C++/ObjC names when displaying symbols is on.
Really redefine built-in command "dump"? (y or n) [answered Y; input not from
terminal]
Reading symbols from cc1...done.
Breakpoint 1 at 0x1a657e2: file /source/gcc-pristine/gcc/diagnostic.c, line
1488.
Breakpoint 2 at 0x1a65559: file /source/gcc-pristine/gcc/diagnostic.c, line
1420.
Breakpoint 3 at 0x76cfd0
Breakpoint 4 at 0x76d0f0
[snip snip]
[snip snip]
Successfully loaded GDB hooks for GCC
(gdb) break fsm_find_control_statement_thread_paths
Breakpoint 5 at 0x118c4e3: file
/source/gcc-pristine/gcc/tree-ssa-threadbackward.c, line 678.
(gdb) run a.c -O2 -quiet
Starting program: /home/build/pristine/gcc/cc1 a.c -O2 -quiet

Breakpoint 5, fsm_find_control_statement_thread_paths (name=
    <ssa_name 0x7fb8fc93c990>, visited_bbs=0x283b0c0, Python Exception <class
'gdb.error'> Cannot convert value to long.: 
path=, 
    seen_loop_phi=false, speed_p=false)
    at /source/gcc-pristine/gcc/tree-ssa-threadbackward.c:678
678       if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (name))
(gdb) print path
$1 = Python Exception <class 'gdb.error'> Cannot convert value to long.: 
(gdb) up
#1  0x000000000118ca93 in find_jump_threads_backwards (
    bb=<basic_block 0x7fb8fc93d270 (2)>, speed_p=false)
    at /source/gcc-pristine/gcc/tree-ssa-threadbackward.c:785
785       fsm_find_control_statement_thread_paths (name, visited_bbs, bb_path,
false,
(gdb) print bb_path
$2 = 0x7fb8fca77000 = {<basic_block 0x7fb8fc93d270 (2)>}