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Re: [PATCH] Fix PR81782


On Fri, Dec 08, 2017 at 03:44:03PM +0100, Richard Biener wrote:
> 
> The following fixes spurious uninit warnings for zero-sized arrays.
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.
> 
> Richard.
> 
> 2017-12-08  Richard Biener  <rguenther@suse.de>
> 
> 	PR middle-end/81782
> 	* tree-ssa-uninit.c (warn_uninitialized_vars): Properly
> 	handle accesses outside of zero-sized vars.

Is ref.max_size == -1 always guaranteeing no access before offset, only
after it?
What I fear is e.g. ARRAY_REF with non-constant index with base of
MEM_REF with & of a middle of array or something similar?
struct S { int x[64]; } foo;
MEM_REF[&foo, 40][i] with negative i.

Anyway, in this case it is about not printing a warning, so we can give up
even if it is theoretically possible.

> --- gcc/tree-ssa-uninit.c	(revision 255499)
> +++ gcc/tree-ssa-uninit.c	(working copy)
> @@ -296,8 +296,8 @@ warn_uninitialized_vars (bool warn_possi
>  	         variable.  */
>  	      if (DECL_P (base)
>  		  && ref.size != -1
> -		  && ref.max_size == ref.size
> -		  && (ref.offset + ref.size <= 0
> +		  && ((ref.max_size == ref.size
> +		       && ref.offset + ref.size <= 0)
>  		      || (ref.offset >= 0
>  			  && DECL_SIZE (base)
>  			  && TREE_CODE (DECL_SIZE (base)) == INTEGER_CST

	Jakub


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