Re: [PATCH 2/2] asm inline

[Marc Glisse <marc.glisse@inria.fr>]

On Sun, 2 Dec 2018, Segher Boessenkool wrote:

> diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
> index 5aa782b..7e9ed99 100644
> --- a/gcc/tree-inline.c
> +++ b/gcc/tree-inline.c
> @@ -4109,6 +4109,9 @@ estimate_num_insns (gimple *stmt, eni_weights *weights)
> 	   with very long asm statements.  */
> 	if (count > 1000)
> 	  count = 1000;
> +	/* If this asm is asm inline, count anything as minimum size.  */
> +	if (gimple_asm_inline_p (as_a <gasm *> (stmt)))
> +	  count = !!count;
> 	return MAX (1, count);
>       }

Hello,

what is the point of !!count when we take the max with 1 on the very
next line? Is it in prevision of a time when we may remove the MAX? (sorry 
if this was covered in previous iterations)

By the way, not related to the patch, but I wonder why we cannot have a
cost of 0. My main use of inline asm is as an optimization barrier:
asm("":"+gx"(local_var))
possibly marked volatile to prevent more optimizations. I certainly
expect it to generate exactly 0 instruction in most cases. Although if I 
am not careful it could easily generate moves from x87 to sse/memory for 
instance. I guess a minimal cost is safer and doesn't affect decisions too 
badly.

-- 
Marc Glisse