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Re: Proposed doc update for Explicit Reg Vars 3/3
- From: Andrew Haley <aph at redhat dot com>
- To: Jeff Law <law at redhat dot com>, Segher Boessenkool <segher at kernel dot crashing dot org>
- Cc: David Wohlferd <dw at LimeGreenSocks dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Sandra Loosemore <sandra at codesourcery dot com>
- Date: Tue, 20 Oct 2015 17:39:41 +0100
- Subject: Re: Proposed doc update for Explicit Reg Vars 3/3
- Authentication-results: sourceware.org; auth=none
- References: <561C3DAE dot 8050505 at LimeGreenSocks dot com> <5625CF7E dot 5010003 at redhat dot com> <20151020151312 dot GB25514 at gate dot crashing dot org> <56266519 dot 8070104 at redhat dot com> <56266630 dot 2050800 at redhat dot com> <562667FF dot 5000003 at redhat dot com> <562668B5 dot 6040404 at redhat dot com> <56266A5D dot 80809 at redhat dot com>
On 10/20/2015 05:22 PM, Jeff Law wrote:
> On 10/20/2015 10:15 AM, Andrew Haley wrote:
>>> But in that case, what do we guarantee.
>>>
>>> We certainly don't guarantee that those objects will be in their
>>> requested register at any point other than at the asm statements.
>>
>> OK, but this usage did work in the past: that it now doesn't is a
>> regression. GCC was quite useful (unique, really) in that it provided
>> a way to write a decent bytecode interpreter in a HLL. The world has
>> lost something significant if this no longer works.
>
> It still works, but again, it's not a guarantee, never has been.
I hear you, but what always mattered most was what happened in
practice, and in practice it worked rather nicely. The question,
then, isn't what we can guarantee but what usually works.
And as we know, the behaviour of GCC isn't driven by the whim of the
maintainers but by the needs of our users, especially kernel
programmers! Authors of interpreters don't have quite so much
influence.
Andrew.