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Re: volatile access optimization (C++ / x86_64)
- From: <Paul_Koning at Dell dot com>
- To: <dj at redhat dot com>
- Cc: <nightstrike at gmail dot com>, <matt at godbolt dot org>, <gcc at gcc dot gnu dot org>
- Date: Mon, 5 Jan 2015 18:40:53 +0000
- Subject: Re: volatile access optimization (C++ / x86_64)
- Authentication-results: sourceware.org; auth=none
- References: <CAFWXXN3quEdSnaoWuPcQn2k-F99Yaw+6=NqgFgcu9ABpv5ZD3Q at mail dot gmail dot com> <xnvbkldsgz dot fsf at greed dot delorie dot com> <CAF1jjLstqa0XxDP-5JDYmi0wNas-bHMTyR6nVt8=SYdMMqxYwg at mail dot gmail dot com> <201501051824 dot t05IOnpd008520 at greed dot delorie dot com>
> On Jan 5, 2015, at 1:24 PM, DJ Delorie <dj@redhat.com> wrote:
>
>
>> What is involved with the auditing?
>
> Each pattern that (directly or indirectly) uses general_operand,
> memory_operand, or nonimmediate_operand needs to be checked to see if
> it's volatile-safe. If so, you need to change the predicate to
> something that explicitly accepts volatiles.
>
> There's been talk about adding direct support for a "volatile-clean"
> flag that avoids this for targets where you know it's correct, which
> bypasses the volatile check in those functions, but it hasn't happened
> yet.
I looked in the documentation and didnât see this described. Is it? Where?
A general flag seems useful, because for most targets it would seen applicable.
paul