On July 27, 2015 5:18:55 PM GMT+02:00, Michael Matz <m...@suse.de> wrote:
>Hi,
>
>On Mon, 27 Jul 2015, Richard Biener wrote:
>
>> > > static inline tree
>> > > gimple_assign_rhs1 (const_gimple gs)
>> > > {
>> > > GIMPLE_CHECK (gs, GIMPLE_ASSIGN);
>> > > return gimple_op (gs, 1);
>> > > }
>> > >
>> > > and the hidden checking is due to gimple_op being
>> > >
>> > > static inline tree *
>> > > gimple_ops (gimple gs)
>> > > {
>> > > size_t off;
>> > >
>> > > /* All the tuples have their operand vector at the very bottom
>> > > of the structure. Note that those structures that do not
>> > > have an operand vector have a zero offset. */
>> > > off = gimple_ops_offset_[gimple_statement_structure (gs)];
>> > > gcc_gimple_checking_assert (off != 0);
>
>I once experimented with making the multiple checking and removing the
>actual memory accesses by exposing the real content of gss_for_code_[]
>(for gss_for_code(), used by gimple_statement_structure()) and
>gimple_ops_offset_[] to the inlined functions, i.e. by defining them in
>
>gimple.h, not just declaring them.
>
>Still wouldn't help the -O0 case, but with -O2 only the first check for
>
>being GIMPLE_ASSING remains, everything else is constant folded.
>
>> > > The simplest thing would be to use
>> > >
>> > > GIMPLE_CHECK (gs, GIMPLE_ASSIGN);
>> > > return as_a <const gassign *> (gs)->op[1];
>> > >
>> > > but that's not optimal either because we check we have a gassign
>> > > again (not optimized in stage1). So I decided to invent a fancy
>> > > as_a which reports errors similar to GIMPLE_CHECK and makes the
>> > > code look like
>
>I'm confused. as_a<> already does checking:
>as_a (U *p)
>{
> gcc_checking_assert (is_a <T> (p));
> return is_a_helper <T>::cast (p);
>}
>
>(were the is_a<> variant here has the same test as GIMPLE_CHECK).
>So, if you have the as_a call, you can as well simply remove the
>GIMPLE_CHECK, and be done with it, without ...
>
>> > > const gassign *ass = GIMPLE_CHECK2<const gassign *> (gs);
>
>... introducing this. What am I missing?
It would remove the fancy checking fail message in favor of a simple ICE.
Otherwise nothing, of course. Oh, and
the ability to separately turn on/off GIMPLE checking.
Richard.
>
>Ciao,
>Michael.
