[Bug c/40305] New: strict aliasing and inlining

[Bug c/40305] New: strict aliasing and inlining

[arnaud dot lb at gmail dot com]

The following code (attaching preprocessed one) crashes with gcc 4.3.3 and gcc
4.4.1 (20090529).

Adding noinline attribute to pop() avoids the crash.

Declaring pop(strict foo *f, void** a) as pop(strict foo *f, int **a) avoids
the crash.

Adding -fno-strict-aliasing avoids the crash.

I'm not sure it does breaks strict aliasing (not the same as casting a "void*"
to a "int*" and dereferencing it). gcc does not prints any warning about strict
aliasing.

Compiled with "gcc-4.4.1 -o out test.c -O3", ran with "./out".

#include <string.h>
#include <assert.h>

struct foo {
        int *a;
        void **top;
        void *storage[1];
};

void crash(struct foo *f);

int main() {
        struct foo f;
        int i = 0;

        memset(&f, 0, sizeof(f));

        f.top = &f.storage[1];
        f.a = &i;

        crash(&f);

        assert(f.top == &f.storage[0]);
        assert(f.a == f.storage[0]);
        assert(f.a == NULL);
}

void pop(struct foo *f, void **a) {
        *a = *(--f->top);
}       

__attribute__((noinline))
void crash(struct foo *f) {

        while (f->a) {
                pop(f, (void**)&f->a);
        }       
}


-- 
           Summary: strict aliasing and inlining
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: arnaud dot lb at gmail dot com
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40305

[Bug c/40305] strict aliasing and inlining

[arnaud dot lb at gmail dot com]

------- Comment #1 from arnaud dot lb at gmail dot com  2009-05-30 13:22 -------
Created an attachment (id=17936)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17936&action=view)
preprocessed code


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40305

[Bug c/40305] strict aliasing and inlining

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2009-05-30 13:50 -------
It is invalid.  f->a is accessed through an incompatible type (void * rather
than int *).  And gcc even warns about it, with -Wstrict-aliasing=2 or
-Wstrict-aliasing=1.


-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40305