[PATCH PR43513, 1/3] Replace vla with array - Implementation.

[Tom de Vries]

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  <tom@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
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