Re: Improve ECF_NOTHROW flags for direct internal functions

[Richard Biener <richard dot guenther at gmail dot com>]

On Thu, Aug 17, 2017 at 11:49 AM, Richard Sandiford
<richard.sandiford@linaro.org> wrote:
> Internal functions that map directly to an optab can only throw an
> exception for -fnon-call-exceptions.  This patch handles that in
> internal_fn_flags, in a similar way to ATTR_*NOTHROW in builtins.def.
>
> (Functions that don't throw even for flag_non_call_exceptions should be
> explicitly marked ECF_NOTHROW in internal-fn.def.)
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Hmm.  Note the outcome of flag_non_call_exceptions depends on the
current function and thus IPA passes querying flags would need to
push an appropriate function context.  This means the function should
get a struct function * argument and opt_for_fn (fn, flag_non_call_exceptions)
should be used.  It doesn't help very much that all callers don't have
any such context either which means this "optimization" looks like
in the wrong place :/  (the global value of flag_non_call_exceptions in
the IPA case isn't necessarily conservative).

So if you insist then add a comment and add a && cfun check so
we're sure we are in non-IPA context (or in properly setup context).

Richard.

> Richard
>
>
> 2017-08-17  Richard Sandiford  <richard.sandiford@linaro.org>
>
> gcc/
>         * internal-fn.h (internal_fn_flags): Just declare and move
>         the actual implementation out-of-line to...
>         * internal-fn.c (internal_fn_flags): ...here.  Set ECF_NOTHROW for
>         directly-mapped internal functions if !flag_non_call_exceptions.
>
> Index: gcc/internal-fn.h
> ===================================================================
> --- gcc/internal-fn.h   2017-02-23 19:54:03.000000000 +0000
> +++ gcc/internal-fn.h   2017-08-17 09:05:37.459968561 +0100
> @@ -107,15 +107,7 @@ internal_fn_name (enum internal_fn fn)
>    return internal_fn_name_array[(int) fn];
>  }
>
> -/* Return the ECF_* flags for function FN.  */
> -
> -extern const int internal_fn_flags_array[];
> -
> -static inline int
> -internal_fn_flags (enum internal_fn fn)
> -{
> -  return internal_fn_flags_array[(int) fn];
> -}
> +extern int internal_fn_flags (enum internal_fn fn);
>
>  /* Return fnspec for function FN.  */
>
> Index: gcc/internal-fn.c
> ===================================================================
> --- gcc/internal-fn.c   2017-08-10 14:36:07.453493083 +0100
> +++ gcc/internal-fn.c   2017-08-17 09:05:37.459968561 +0100
> @@ -2814,3 +2814,18 @@ expand_PHI (internal_fn, gcall *)
>  {
>      gcc_unreachable ();
>  }
> +
> +/* Return the ECF_* flags for function FN.  */
> +
> +int
> +internal_fn_flags (enum internal_fn fn)
> +{
> +  int flags = internal_fn_flags_array[(int) fn];
> +  /* Functions that map to optabs can only throw a catchable exception
> +     when non-call exceptions are enabled.  The non-call exceptions in
> +     these cases will typically come from things like IEEE exceptions,
> +     divide by zero errors and SEGVs.  */
> +  if (direct_internal_fn_p (fn) && !flag_non_call_exceptions)
> +    flags |= ECF_NOTHROW;
> +  return flags;
> +}