Re: [PATCH v5 2/4] tree-object-size: Handle function parameters

[Jakub Jelinek <jakub@redhat.com>]

On Sat, Dec 18, 2021 at 06:05:09PM +0530, Siddhesh Poyarekar wrote:
> @@ -1440,6 +1441,53 @@ cond_expr_object_size (struct object_size_info *osi, tree var, gimple *stmt)
>    return reexamine;
>  }
>  
> +/* Find size of an object passed as a parameter to the function.  */
> +
> +static void
> +parm_object_size (struct object_size_info *osi, tree var)
> +{
> +  int object_size_type = osi->object_size_type;
> +  tree parm = SSA_NAME_VAR (var);
> +
> +  if (!(object_size_type & OST_DYNAMIC) || !POINTER_TYPE_P (TREE_TYPE (parm)))
> +    expr_object_size (osi, var, parm);

This looks very suspicious.  Didn't you mean { expr_object_size (...); return; } here?
Because the code below e.g. certainly assumes OST_DYNAMIC and that TREE_TYPE (parm)
is a pointer type (otherwise TREE_TYPE (TREE_TYPE (...) wouldn't work.

> +
> +  /* Look for access attribute.  */
> +  rdwr_map rdwr_idx;
> +
> +  tree fndecl = cfun->decl;
> +  const attr_access *access = get_parm_access (rdwr_idx, parm, fndecl);
> +  tree typesize = TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (parm)));
> +  tree sz = NULL_TREE;
> +
> +  if (access && access->sizarg != UINT_MAX)

Perhaps && typesize here?  It makes no sense to e.g. create ssa default def
when you aren't going to use it in any way.

> +    {
> +      tree fnargs = DECL_ARGUMENTS (fndecl);
> +      tree arg = NULL_TREE;
> +      unsigned argpos = 0;
> +
> +      /* Walk through the parameters to pick the size parameter and safely
> +	 scale it by the type size.  */
> +      for (arg = fnargs; argpos != access->sizarg && arg;
> +	   arg = TREE_CHAIN (arg), ++argpos);

Instead of a loop with empty body wouldn't it be better to
do the work in that for loop?
I.e. take argpos != access->sizarg && from the condition,
replace arg != NULL_TREE with that argpos == access->sizarg
and add a break;?

> +
> +      if (arg != NULL_TREE && INTEGRAL_TYPE_P (TREE_TYPE (arg)))
> +	{
> +	  sz = get_or_create_ssa_default_def (cfun, arg);

Also, I must say I'm little bit worried about this
get_or_create_ssa_default_def call.  If the SSA_NAME doesn't exist,
so you create it and then attempt to use it but in the end don't
because e.g. some PHI's another argument was unknown etc., will
that SSA_NAME be released through release_ssa_name?
I think GIMPLE is fairly unhappy if there are SSA_NAMEs created and not
released that don't appear in the IL anywhere.

> +	  if (sz != NULL_TREE)
> +	    {
> +	      sz = fold_convert (sizetype, sz);
> +	      if (typesize)
> +		sz = size_binop (MULT_EXPR, sz, typesize);
> +	    }
> +	}
> +    }

	Jakub