[Bug c++/107504] New: Debugger jumps back to structured binding declaration

[Bug c++/107504] New: Debugger jumps back to structured binding declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

            Bug ID: 107504
           Summary: Debugger jumps back to structured binding declaration
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

struct S
{
  void* i;
  int j;
};

S f(char* p)
{
  return {p, 1};
}

int main()
{
  char buf[1];
  auto [x, y] = f(buf);
  if (x != buf)
    throw 1;
  if (y != 1)
    throw 2;
  return 0;
}

Compiled with -g the debugger shows control jumping backwards to the structured
binding declaration:

$ gdb --quiet -ex start -ex n -ex n -ex n -ex n a.out
Reading symbols from a.out...
Temporary breakpoint 1 at 0x40115f: file sb.C, line 15.
Starting program: /tmp/a.out 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Temporary breakpoint 1, main () at sb.C:15
15        auto [x, y] = f(buf);
16        if (x != buf)
15        auto [x, y] = f(buf);
18        if (y != 1)
20        return 0;


For a slightly larger piece of code I see it jump back to it three times:

$ gdb --quiet -ex start -ex step  -ex n -ex n -ex n -ex n -ex n -ex n -ex n
a.out
Reading symbols from a.out...
Temporary breakpoint 1 at 0x405aa3: file fton.C, line 43.
Starting program: /tmp/a.out 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Temporary breakpoint 1, main () at fton.C:43
43        test();
test () at fton.C:14
14        char buf[4] = { };
15        auto [out, len] = std::format_to_n(buf, 3, "123 + 456 = {}", 579);
16        VERIFY( out == buf+3 );
15        auto [out, len] = std::format_to_n(buf, 3, "123 + 456 = {}", 579);
16        VERIFY( out == buf+3 );
15        auto [out, len] = std::format_to_n(buf, 3, "123 + 456 = {}", 579);
17        VERIFY( len == 15 );
19        std::locale loc({}, new punct);

Notice line 15 occurs three times. I haven't been able to reproduce that in the
minimized test case.

[Bug c++/107504] Debugger jumps back to structured binding declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
          Component|debug                       |c++
           Keywords|                            |wrong-debug
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-11-01

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---

        [/app/example.cpp:15:22] _2 = [/app/example.cpp:15:22] D.2776.j;
        [/app/example.cpp:18:3] if (_2 != 1) goto <D.2822>; else goto <D.2823>;

Most likely because the COMPONENT_REF has a line # on it:

    void * x [value-expr: [/app/example.cpp:15:22] D.2776.i];
    int y [value-expr: [/app/example.cpp:15:22] D.2776.j];

Seems like if we remove that, this would work.

[Bug c++/107504] Debugger jumps back to structured binding declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The code that creates the COMPONENT_REF is the call to
finish_non_static_data_member around decl.cc:9186 .

[Bug c++/107504] Debugger jumps back to structured binding declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I'm also seeing similar jumps back and forth in the debugger for the bodies of
lambda expressions, where the debugger keeps jumping back to the capture list
of the lambda:


$ cat lambda.cc 
int main(int argc, char**)
{
  int x = 1;
  auto f = [&x, &argc](const char* i) {
    i += x;
    i -= argc;
    i += argc - x;
    return i;
  };
  f("          ");
}
$ g++ -g lambda.cc -o lambda
$ gdb -q -ex start -ex 'py [gdb.execute("step") for n in range(14)]' ./lambda
Reading symbols from ./lambda...
Temporary breakpoint 1 at 0x40117a: file lambda.cc, line 3.
Starting program: /tmp/lambda 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Temporary breakpoint 1, main (argc=1) at lambda.cc:3
3         int x = 1;
9         };
10        f("          ");
operator() (__closure=0x7fffffffda60, i=0x402004 "          ") at lambda.cc:5
5           i += x;
4         auto f = [&x, &argc](const char* i) {
5           i += x;
6           i -= argc;
4         auto f = [&x, &argc](const char* i) {
6           i -= argc;
7           i += argc - x;
4         auto f = [&x, &argc](const char* i) {
7           i += argc - x;
4         auto f = [&x, &argc](const char* i) {
7           i += argc - x;
8           return i;

We keep returning to line 4 (the capture) every time the captured variiable is
odr-used.

[Bug c++/107504] Debugger jumps back to structured binding declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #3)
> I'm also seeing similar jumps back and forth in the debugger for the bodies
> of lambda expressions, where the debugger keeps jumping back to the capture
> list of the lambda:

Yes see PR 84471 for the lambda issue.

[Bug c++/107504] Debugger jumps back to structured binding declaration

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/107504] Debugger jumps back to structured binding declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:302485a70a33f3a86e85ad9051de2b51c5dc0bc0

commit r13-4812-g302485a70a33f3a86e85ad9051de2b51c5dc0bc0
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Dec 1 22:58:28 2022 -0500

    c++: source position of lambda captures [PR84471]

    If the DECL_VALUE_EXPR of a VAR_DECL has EXPR_LOCATION set, then any use of
    that variable looks like it has that location, which leads to the debugger
    jumping back and forth for both lambdas and structured bindings.

    Rather than fix all the uses, it seems simplest to remove any EXPR_LOCATION
    when setting DECL_VALUE_EXPR.  So the cp/ hunks aren't necessary, but they
    avoid the need to unshare to remove the location.

            PR c++/84471
            PR c++/107504

    gcc/cp/ChangeLog:

            * coroutines.cc (transform_local_var_uses): Don't
            specify a location for DECL_VALUE_EXPR.
            * decl.cc (cp_finish_decomp): Likewise.

    gcc/ChangeLog:

            * fold-const.cc (protected_set_expr_location_unshare): Not static.
            * tree.h: Declare it.
            * tree.cc (decl_value_expr_insert): Use it.

    include/ChangeLog:

            * ansidecl.h (ATTRIBUTE_WARN_UNUSED_RESULT): Add __.

    gcc/testsuite/ChangeLog:

            * g++.dg/tree-ssa/value-expr1.C: New test.
            * g++.dg/tree-ssa/value-expr2.C: New test.
            * g++.dg/analyzer/pr93212.C: Move warning.

[Bug c++/107504] Debugger jumps back to structured binding declaration

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107504

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|---                         |13.0
         Resolution|---                         |FIXED

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed.