Bug 240819

Created attachment 155143 [details]
Tarball of GCC miscompiling problem, just type make check

That's not a GCC bug, but documented behavior.
USTR_CONF_e_PROTO
int ustrp__rw_realloc(void *, struct Ustr **, int, size_t, size_t)
    USTR__COMPILE_ATTR_WARN_UNUSED_RET() USTR__COMPILE_ATTR_NONNULL_A();
where USTR__COMPILE_ATTR_NONNULL_A() expands to __attribute__((nonnull)).
This means you say that the first and second arguments to the function
must be non-null.
`nonnull (ARG-INDEX, ...)'
     The `nonnull' attribute specifies that some function parameters
     should be non-null pointers.  For instance, the declaration:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                __attribute__((nonnull (1, 2)));

     causes the compiler to check that, in calls to `my_memcpy',
     arguments DEST and SRC are non-null.  If the compiler determines
     that a null pointer is passed in an argument slot marked as
     non-null, and the `-Wnonnull' option is enabled, a warning is
     issued.  The compiler may also choose to make optimizations based
     on the knowledge that certain function arguments will not be null.

     If no argument index list is given to the `nonnull' attribute, all
     pointer arguments are marked as non-null.  To illustrate, the
     following declaration is equivalent to the previous example:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                __attribute__((nonnull));

Especially note the 'The compiler may also choose'... sentence.
With -O2 the compiler chose to take advantage of that guarantee (in VRP pass
particularly), but at runtime you violated that promise.

int ustrp__rw_realloc(void *, struct Ustr **, int, size_t, size_t)
    USTR__COMPILE_ATTR_WARN_UNUSED_RET() USTR__COMPILE_ATTR_NONNULL_A();


...argghhh ... damn, I was looking for a screwup like that on the external
functions, for some reason I didn't think about the internal ones. Sorry, and
thanks Jackub.