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Re: Deprecating basic asm in a function - What now?
- From: Florian Weimer <fweimer at redhat dot com>
- To: Andrew Haley <aph at redhat dot com>, Michael Matz <matz at suse dot de>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Wed, 22 Jun 2016 10:59:40 +0200
- Subject: Re: Deprecating basic asm in a function - What now?
- Authentication-results: sourceware.org; auth=none
- References: <dc3ca16c-3521-757f-fcf0-50061f510f75 at LimeGreenSocks dot com> <alpine dot LSU dot 2 dot 20 dot 1606201931460 dot 13156 at wotan dot suse dot de> <57682A85 dot 4060803 at redhat dot com>
On 06/20/2016 07:40 PM, Andrew Haley wrote:
> On 20/06/16 18:36, Michael Matz wrote:
>> I see zero gain by deprecating them and only churn. What would be the
>> advantage again?
>
> Correctness. It is very likely that many of these basic asms are not
> robust in the face of compiler changes because they don't declare
> their dependencies and therefore work only by accident.
But the correctness problem is much more severe with extended asm. With
basic asm, the compiler can be conservative. With extended asm, there
is an expectation that it is not, and yet many of the constraints out
there are slightly wrong and can lead to breakage any time.
Florian