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Re: [c++-delayed-folding] fold_simple
- From: Kai Tietz <ktietz70 at googlemail dot com>
- To: Jason Merrill <jason at redhat dot com>
- Cc: gcc-patches List <gcc-patches at gcc dot gnu dot org>
- Date: Thu, 27 Aug 2015 11:21:26 +0200
- Subject: Re: [c++-delayed-folding] fold_simple
- Authentication-results: sourceware.org; auth=none
- References: <55DE7C84 dot 8080206 at redhat dot com>
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.
> Jason
Kai