On Wed, 21 May 2014, Richard Biener wrote:
> On Wed, 21 May 2014, Richard Biener wrote:
>
> >
> > PR56955 prompted me to handle BUILT_IN_REALLOC just the same
> > way we already handle BUILT_IN_STR[N]DUP.
> >
> > Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> >
> > Now this will disambiguate *p and *q for p = realloc (q, n)
> > for any value of n (including those that don't actually
> > trigger re-allocation and thus where p == q after the call).
> > I don't think that any such use would be valid - but I can
> > certainly play safer here and implement the points-to part
> > as a pass-through (that is, make p point to what q points).
> > That's of course less optimization.
>
> Like with incremental
>
> Index: gcc/tree-ssa-structalias.c
> ===================================================================
> --- gcc/tree-ssa-structalias.c.orig 2014-05-21 15:37:58.762890034
> +0200
> +++ gcc/tree-ssa-structalias.c 2014-05-21 15:35:52.044898758 +0200
> @@ -4313,6 +4313,17 @@ find_func_aliases_for_builtin_call (stru
> process_all_all_constraints (lhsc, rhsc);
> lhsc.release ();
> rhsc.release ();
> + /* For realloc the resulting pointer can be equal to the
> + argument as well. But only doing this wouldn't be
> + correct because with ptr == 0 realloc behaves like malloc.
> */
> + if (DECL_FUNCTION_CODE (fndecl) == BUILT_IN_REALLOC)
> + {
> + get_constraint_for (gimple_call_lhs (t), &lhsc);
> + get_constraint_for (gimple_call_arg (t, 0), &rhsc);
> + process_all_all_constraints (lhsc, rhsc);
> + lhsc.release ();
> + rhsc.release ();
> + }
> return true;
> }
> break;
>
> that of course makes it a somewhat pointless excercise if
> points-to doesn't figure out sth fancy for the argument to
> realloc (like its NULL or the result of an earlier malloc call,
> still optimizes the testcase as expected).
The following is what I have applied after bootstrapping and
testing on x86_64-unknown-linux-gnu.
Richard.
2014-05-21 Richard Biener <rguent...@suse.de>
* tree-ssa-alias.c (ref_maybe_used_by_call_p_1): Handle
BUILT_IN_REALLOC like BUILT_IN_STRDUP.
(call_may_clobber_ref_p_1): Handle BUILT_IN_REALLOC as allocation
and deallocation site.
* tree-ssa-structalias.c (find_func_aliases_for_builtin_call):
Handle BUILT_IN_REALLOC similar to BUILT_IN_STRDUP with also
passing through the incoming points-to set.
(handle_lhs_call): Use flags argument instead of recomputing it.
(find_func_aliases_for_call): Call handle_lhs_call with proper
call return flags.
* gcc.dg/tree-ssa/alias-33.c: New testcase.
Index: gcc/tree-ssa-alias.c
===================================================================
*** gcc/tree-ssa-alias.c.orig 2014-05-21 16:21:18.995711011 +0200
--- gcc/tree-ssa-alias.c 2014-05-22 09:44:40.940400943 +0200
*************** ref_maybe_used_by_call_p_1 (gimple call,
*** 1594,1599 ****
--- 1594,1600 ----
/* These read memory pointed to by the first argument. */
case BUILT_IN_STRDUP:
case BUILT_IN_STRNDUP:
+ case BUILT_IN_REALLOC:
{
ao_ref dref;
tree size = NULL_TREE;
*************** call_may_clobber_ref_p_1 (gimple call, a
*** 1991,1996 ****
--- 1992,2006 ----
tree ptr = gimple_call_arg (call, 0);
return ptr_deref_may_alias_ref_p_1 (ptr, ref);
}
+ /* Realloc serves both as allocation point and deallocation point. */
+ case BUILT_IN_REALLOC:
+ {
+ tree ptr = gimple_call_arg (call, 0);
+ /* Unix98 specifies that errno is set on allocation failure. */
+ return ((flag_errno_math
+ && targetm.ref_may_alias_errno (ref))
+ || ptr_deref_may_alias_ref_p_1 (ptr, ref));
+ }
case BUILT_IN_GAMMA_R:
case BUILT_IN_GAMMAF_R:
case BUILT_IN_GAMMAL_R:
Index: gcc/tree-ssa-structalias.c
===================================================================
*** gcc/tree-ssa-structalias.c.orig 2014-05-21 16:21:18.995711011 +0200
--- gcc/tree-ssa-structalias.c 2014-05-22 09:43:05.807407492 +0200
*************** handle_lhs_call (gimple stmt, tree lhs,
*** 3974,3980 ****
/* If the call returns an argument unmodified override the rhs
constraints. */
- flags = gimple_call_return_flags (stmt);
if (flags & ERF_RETURNS_ARG
&& (flags & ERF_RETURN_ARG_MASK) < gimple_call_num_args (stmt))
{
--- 3974,3979 ----
*************** find_func_aliases_for_builtin_call (stru
*** 4299,4307 ****
return true;
case BUILT_IN_STRDUP:
case BUILT_IN_STRNDUP:
if (gimple_call_lhs (t))
{
! handle_lhs_call (t, gimple_call_lhs (t), gimple_call_flags (t),
vNULL, fndecl);
get_constraint_for_ptr_offset (gimple_call_lhs (t),
NULL_TREE, &lhsc);
--- 4298,4308 ----
return true;
case BUILT_IN_STRDUP:
case BUILT_IN_STRNDUP:
+ case BUILT_IN_REALLOC:
if (gimple_call_lhs (t))
{
! handle_lhs_call (t, gimple_call_lhs (t),
! gimple_call_return_flags (t) | ERF_NOALIAS,
vNULL, fndecl);
get_constraint_for_ptr_offset (gimple_call_lhs (t),
NULL_TREE, &lhsc);
*************** find_func_aliases_for_builtin_call (stru
*** 4312,4317 ****
--- 4313,4329 ----
process_all_all_constraints (lhsc, rhsc);
lhsc.release ();
rhsc.release ();
+ /* For realloc the resulting pointer can be equal to the
+ argument as well. But only doing this wouldn't be
+ correct because with ptr == 0 realloc behaves like malloc. */
+ if (DECL_FUNCTION_CODE (fndecl) == BUILT_IN_REALLOC)
+ {
+ get_constraint_for (gimple_call_lhs (t), &lhsc);
+ get_constraint_for (gimple_call_arg (t, 0), &rhsc);
+ process_all_all_constraints (lhsc, rhsc);
+ lhsc.release ();
+ rhsc.release ();
+ }
return true;
}
break;
*************** find_func_aliases_for_call (struct funct
*** 4535,4541 ****
else
handle_rhs_call (t, &rhsc);
if (gimple_call_lhs (t))
! handle_lhs_call (t, gimple_call_lhs (t), flags, rhsc, fndecl);
rhsc.release ();
}
else
--- 4547,4554 ----
else
handle_rhs_call (t, &rhsc);
if (gimple_call_lhs (t))
! handle_lhs_call (t, gimple_call_lhs (t),
! gimple_call_return_flags (t), rhsc, fndecl);
rhsc.release ();
}
else
Index: gcc/testsuite/gcc.dg/tree-ssa/alias-33.c
===================================================================
*** /dev/null 1970-01-01 00:00:00.000000000 +0000
--- gcc/testsuite/gcc.dg/tree-ssa/alias-33.c 2014-05-22 09:43:05.808407492
+0200
***************
*** 0 ****
--- 1,20 ----
+ /* { dg-do run } */
+ /* { dg-options "-O -fdump-tree-fre1-details" } */
+
+ int j;
+ int main ()
+ {
+ int i = 1;
+ int **p;
+ j = 0;
+ p = __builtin_malloc (sizeof (int *));
+ *p = &i;
+ p = __builtin_realloc (p, 2 * sizeof (int *));
+ **p = 0;
+ if (i != 0)
+ __builtin_abort ();
+ return j;
+ }
+
+ /* { dg-final { scan-tree-dump "Replaced j with 0" "fre1" } } */
+ /* { dg-final { cleanup-tree-dump "fre1" } } */
