Re: C++: Letting compiler know asm block can call function that can throw?

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

On Thu, Mar 29, 2012 at 3:59 PM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Thu, 29 Mar 2012, Stephan Bergmann wrote:
>
>> > > Anyway, would it be worthwhile filing an RFE for an asm annotation
>> > > telling the compiler that it contains code that can throw?
>> >
>> > I suppose yes.
>>
>> <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52770> "RFE: Letting
>> compiler know asm block can call function that can throw."
>
> Actually, with -fnon-call-exceptions volatile asms are already supposed to
> be throwing. ?It's just that this got lost with tree-ssa. ?With the patch
> and -fnon-call-exceptions a simple "__asm__ volatile (...)" is regarded as
> possibly throwing.
>
> Without -fnon-call-exceptions some parser changes would be required. ?How
> about "asm throw (...)" ?
>
>
> Ciao,
> Michael.
> Index: tree-eh.c
> ===================================================================
> --- tree-eh.c ? (revision 183716)
> +++ tree-eh.c ? (working copy)
> @@ -1959,6 +1959,7 @@ lower_eh_constructs_2 (struct leh_state
> ? ? ? }
> ? ? ? /* FALLTHRU */
>
> + ? ?case GIMPLE_ASM:
> ? ? case GIMPLE_ASSIGN:
> ? ? ? /* If the stmt can throw use a new temporary for the assignment
> ? ? ? ? ?to a LHS. ?This makes sure the old value of the LHS is

This does not handle using a temporary for all (register) outputs ...
I suppose the code should walk all SSA defs instead of looking at
the LHS only.

> Index: tree-cfg.c
> ===================================================================
> --- tree-cfg.c ?(revision 183716)
> +++ tree-cfg.c ?(working copy)
> @@ -580,6 +580,8 @@ make_edges (void)
>
> ? ? ? ? ? ?case GIMPLE_ASM:
> ? ? ? ? ? ? ?make_gimple_asm_edges (bb);
> + ? ? ? ? ? ? if (is_ctrl_altering_stmt (last))
> + ? ? ? ? ? ? ? make_eh_edges (last);
> ? ? ? ? ? ? ?fallthru = true;
> ? ? ? ? ? ? ?break;

Otherwise this looks reasonable.  With a testcase, I suppose ;)

Richard.