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Re: Fix up -fexcess-precision handling in LTO (was Re: [GCC][middle-end] Add rules to strip away unneeded type casts in expressions (2nd patch))
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Richard Biener <rguenther at suse dot de>, Tamar Christina <Tamar dot Christina at arm dot com>, <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 19 Aug 2019 22:03:53 +0000
- Subject: Re: Fix up -fexcess-precision handling in LTO (was Re: [GCC][middle-end] Add rules to strip away unneeded type casts in expressions (2nd patch))
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On Tue, 30 Jul 2019, Jakub Jelinek wrote:
> Furthermore, some comments claimed that the proper EXCESS_PRECISION_STANDARD
> handling requires FE support, but that also doesn't seem to be the case
> these days, some FEs even just use EXCESS_PRECISION_STANDARD by default
> (go, D).
> So, the following patch gets rid of flag_excess_precision and renames
> flag_excess_precision_cmdline to flag_excess_precision, plus adds
> Optimization flag to that command line option, so that we remember it during
> compilation and e.g. during LTO can then have some functions with standard
> excess precision and others with fast excess precision.
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK minus the removal of the comment in lhd_post_options. Proper handling
requires front-end support (to generate GIMPLE with the operations in the
intended type). Back-end support (to avoid having insn patterns claiming
to operate on the types the processor in fact does not have direct support
for arithmetic on), although not strictly required, is a very good idea,
to make it more obvious if something is wrongly generating arithmetic on
inappropriate types. And then you need the middle-end support (to avoid
transformations introducing operations in the types that aren't meant to
have direct operations, even if in fact the semantics are equivalent) as
Joseph S. Myers