[Bug c/109450] New: Wrong code for VLA in struct sithe size expression

[Bug c/109450] New: Wrong code for VLA in struct sithe size expression

[muecker at gwdg dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109450

            Bug ID: 109450
           Summary: Wrong code for VLA in struct sithe size expression
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: muecker at gwdg dot de
  Target Milestone: ---

The following code should return 1 but returns two. 

int bar(int n, struct foo* x)
{
        int a = n;
        struct foo { char buf[n++]; }* p = x;
        return a;
}

int main()
{
    return bar(1, 0);
}



https://godbolt.org/z/e94dsfhc9


I noticed this when working on a fix for PR107557 and PR108423.

Already affects 4.7.3 and maybe earlier.

[Bug c/109450] Wrong code for VLA in struct sithe size expression

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109450

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code,
                   |                            |wrong-code

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The issue is related to struct foo in the function declaration.

With a slightly modified code you can get an ICE instead:
int bar(int n, struct foo *x)
{
        int a = n;
        struct foo { char buf[a++]; }* p = x;
        return n == a;
}

int main()
{
    return bar(1, 0);
}

[Bug c/109450] VLA struct definition vs use in the function declaration

[muecker at gwdg dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109450

--- Comment #2 from Martin Uecker <muecker at gwdg dot de> ---
This is unrelated to PR29970. The cause of this is that gimplify_parm_type
recurses into incomplete types which is wrong for the same reason as in
gimplify_type_sizes.

[Bug c/109450] VLA struct definition vs use in the function declaration

[muecker at gwdg dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109450

--- Comment #3 from Martin Uecker <muecker at gwdg dot de> ---
PATCH: https://gcc.gnu.org/pipermail/gcc-patches/2023-May/618911.html

[Bug c/109450] VLA struct definition vs use in the function declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109450

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Uecker <uecker@gcc.gnu.org>:

https://gcc.gnu.org/g:42d1612eb5c3b2ee327bc3336bfcbc43a0d0fc5b

commit r14-1143-g42d1612eb5c3b2ee327bc3336bfcbc43a0d0fc5b
Author: Martin Uecker <uecker@tugraz.at>
Date:   Sun May 21 19:32:01 2023 +0200

    Fix ICEs related to VM types in C 2/2 [PR109450]

    Size expressions were sometimes lost and not gimplified correctly,
    leading to ICEs and incorrect evaluation order.  Fix this by 1) not
    recursing pointers when gimplifying parameters, which was incorrect
    because it might access variables declared later for incomplete
    structs, and 2) adding a decl expr for variably-modified arrays
    that are pointed to by parameters declared as arrays.

            PR c/109450

            gcc/
            * function.cc (gimplify_parm_type): Remove function.
            (gimplify_parameters): Call gimplify_type_sizes.

            gcc/c/
            * c-decl.cc (add_decl_expr): New function.
            (grokdeclarator): Add decl expr for size expression in
            types pointed to by parameters declared as arrays.

            gcc/testsuite/
            * gcc.dg/pr109450-1.c: New test.
            * gcc.dg/pr109450-2.c: New test.
            * gcc.dg/vla-26.c: New test.

[Bug c/109450] VLA struct definition vs use in the function declaration

[uecker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109450

uecker at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |uecker at gcc dot gnu.org
   Target Milestone|---                         |14.0

--- Comment #5 from uecker at gcc dot gnu.org ---
fixed on trunk.

[Bug c/109450] VLA struct definition vs use in the function declaration

[uecker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109450

uecker at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from uecker at gcc dot gnu.org ---
fixed on trunk.