[Bug fortran/65921] New: GFortran should use __builtin_mul_overflow when checking allocation sizes

[jb at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65921

            Bug ID: 65921
           Summary: GFortran should use __builtin_mul_overflow when
                    checking allocation sizes
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jb at gcc dot gnu.org
  Target Milestone: ---

As of the GCC-5 release there is a new __builtin_mul_overflow builtin
(https://gcc.gnu.org/gcc-5/changes.html ). GFortran could use this instead of
the current overflow checks

1) In the frontend, code generated for the ALLOCATE statement.

2) In libgfortran/runtime/memory.c (xmallocarray).