[Bug tree-optimization/58480] New: Use attribute((nonnull)) to optimize callers

[Bug tree-optimization/58480] New: Use attribute((nonnull)) to optimize callers

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58480

            Bug ID: 58480
           Summary: Use attribute((nonnull)) to optimize callers
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org

Hello,

in this first function, gcc knows that p is not zero and removes the test (I
have to make sure q doesn't disappear too early, or the compiler forgets that p
is dereferenced, maybe when vrp information becomes persistent...):

int f(int*p){
  int q=*p;
  if(!p) __builtin_abort();
  return q;
}

However, in the following:

void g(int*p,int*q){
  __builtin_memcpy(q,p,4);
  if(!p) __builtin_abort();
}

the test isn't removed, although calling memcpy with a zero argument is just as
bad a dereferencing 0.

Replacing __builtin_memcpy with this doesn't help either:

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

However, this is optimized:

__attribute__((nonnull))void g(int*p){
  if(!p) __builtin_abort();
}

So I think gcc should make use of the nonnull attribute for optimization
purposes not just inside the function, but in the callers as well (and make
sure whatever we do for the nonnull attribute applies to __builtin_memcpy as
well).

[Bug tree-optimization/58480] Use attribute((nonnull)) to optimize callers

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58480

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
Author: glisse
Date: Tue Oct  8 10:39:49 2013
New Revision: 203271

URL: http://gcc.gnu.org/viewcvs?rev=203271&root=gcc&view=rev
Log:
2013-10-08  Marc Glisse  <marc.glisse@inria.fr>

    PR tree-optimization/58480
gcc/
    * tree-vrp.c (infer_nonnull_range): New function.
    (infer_value_range): Call infer_nonnull_range.

gcc/testsuite/
    * gcc.dg/tree-ssa/pr58480.c: New file.

Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr58480.c   (with props)
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vrp.c

Propchange: trunk/gcc/testsuite/gcc.dg/tree-ssa/pr58480.c
            ('svn:eol-style' added)

Propchange: trunk/gcc/testsuite/gcc.dg/tree-ssa/pr58480.c
            ('svn:keywords' added)

[Bug tree-optimization/58480] Use attribute((nonnull)) to optimize callers

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58480

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED
           Assignee|unassigned at gcc dot gnu.org      |glisse at gcc dot gnu.org

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> ---
Done for 4.9.