On 09/24/2011 05:29 PM, Eric Botcazou wrote:
>> This is an updated version of the patch. I have 2 new patches and an
>> updated testcase which I will sent out individually.
>>
>> Patch set was bootstrapped and reg-tested on x86_64.
>>
>> Ok for trunk?
>>
>> Thanks,
>> - Tom
>>
>> 2011-07-30 Tom de Vries <t...@codesourcery.com>
>>
>> PR middle-end/43513
>> * Makefile.in (tree-ssa-ccp.o): Add $(PARAMS_H) to rule.
>> * tree-ssa-ccp.c (params.h): Include.
>> (fold_builtin_alloca_for_var): New function.
>> (ccp_fold_stmt): Use fold_builtin_alloca_for_var.
>
> We have detected another fallout on some Ada code: the transformation
> replaces
> a call to __builtin_alloca with &var, i.e. it introduces an aliased variable,
> which invalidates the points-to information of some subsequent call, fooling
> DSE into thinking that it can eliminate a live store.
>
> The brute force approach
>
> Index: tree-ssa-ccp.c
> ===================================================================
> --- tree-ssa-ccp.c (revision 179038)
> +++ tree-ssa-ccp.c (working copy)
> @@ -2014,7 +2014,10 @@ do_ssa_ccp (void)
> ccp_initialize ();
> ssa_propagate (ccp_visit_stmt, ccp_visit_phi_node);
> if (ccp_finalize ())
> - return (TODO_cleanup_cfg | TODO_update_ssa | TODO_remove_unused_locals);
> + return (TODO_cleanup_cfg
> + | TODO_update_ssa
> + | TODO_rebuild_alias
> + | TODO_remove_unused_locals);
> else
> return 0;
> }
>
> works, but we might want to be move clever. Thoughts?
>
How about attached (untested) patch implementing a conservative, but
runtime-efficient approach?
Thanks,
- Tom
Index: gcc/tree-ssa-ccp.c
===================================================================
--- gcc/tree-ssa-ccp.c (revision 179043)
+++ gcc/tree-ssa-ccp.c (working copy)
@@ -1729,6 +1729,7 @@ fold_builtin_alloca_for_var (gimple stmt
array_type = build_array_type_nelts (elem_type, n_elem);
var = create_tmp_var (array_type, NULL);
DECL_ALIGN (var) = align;
+ pt_solution_add_var (&get_ptr_info (lhs)->pt, var);
/* Fold alloca to the address of the array. */
return fold_convert (TREE_TYPE (lhs), build_fold_addr_expr (var));
Index: gcc/tree-ssa-alias.h
===================================================================
--- gcc/tree-ssa-alias.h (revision 179043)
+++ gcc/tree-ssa-alias.h (working copy)
@@ -125,6 +125,7 @@ extern void dump_alias_stats (FILE *);
/* In tree-ssa-structalias.c */
extern unsigned int compute_may_aliases (void);
+extern void pt_solution_add_var (struct pt_solution *, tree);
extern bool pt_solution_empty_p (struct pt_solution *);
extern bool pt_solution_includes_global (struct pt_solution *);
extern bool pt_solution_includes (struct pt_solution *, const_tree);
Index: gcc/tree-ssa-structalias.c
===================================================================
--- gcc/tree-ssa-structalias.c (revision 179043)
+++ gcc/tree-ssa-structalias.c (working copy)
@@ -5952,6 +5952,14 @@ pt_solution_ior_into (struct pt_solution
bitmap_ior_into (dest->vars, src->vars);
}
+void
+pt_solution_add_var (struct pt_solution *dest, tree var)
+{
+ struct pt_solution var_pt;
+ pt_solution_set_var (&var_pt, var);
+ pt_solution_ior_into (dest, &var_pt);
+}
+
/* Return true if the points-to solution *PT is empty. */
bool
