Re: [c++-delayed-folding] fold_simple

[Kai Tietz <ktietz70 at googlemail dot com>]

2015-08-27 12:34 GMT+02:00 Richard Biener <richard.guenther@gmail.com>:
> On Thu, Aug 27, 2015 at 11:21 AM, Kai Tietz <ktietz70@googlemail.com> wrote:
>> 2015-08-27 4:57 GMT+02:00 Jason Merrill <jason@redhat.com>:
>>> Why does fold_simple fold so many patterns?  I thought we wanted something
>>> that would just fold conversions and negations of constant values.
>>
>> Yes, initial variant was handling much less patterns.  But actually we
>> need for functions (eg. like build_vec_init in init.c) a simple
>> routine to perform basic constant-value arithmetics (sizeof * / + -
>> trunc, etc) to avoid call of maybe_constant_value.  Also for
>> overflow-diagnostics we want at least to resolve such simple patterns
>> for constant-values only.  We could change those calls to use
>> maybe_constant_value instead, but the overhead (and some of its
>> folding) leads much further then working on constant-values only (as
>> fold_simple does).
>>
>> It might be that we can remove the ternary vector-cond expression from
>> this routine, The cond-expr itself seems to be necessary to resolve
>> patterns like (1 == 1 ? 32 : 64), which can appear pretty often via
>> macro-code.  I will check if I what patterns I can remove here.
>
> Note that fold-const.c has constant-only folding routines (handling only
> constant operands).  const_unop, const_binop (no const_ternop split
> out yet).
>
> Richard.

Thanks for the point.  I will take a look into cons_unop/binop.  I
just expect that this routines would fail if they get c++-expressions,
aren't they?

>>> Jason

Kai