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Re: PING: [PATCH] PR target/67215: -fno-plt needs improvements for x86
- From: Ramana Radhakrishnan <ramana dot radhakrishnan at foss dot arm dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: Jiong Wang <jiong dot wang at foss dot arm dot com>, Bernd Schmidt <bschmidt at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Marcus Shawcroft <Marcus dot Shawcroft at arm dot com>
- Date: Tue, 27 Oct 2015 15:42:04 +0000
- Subject: Re: PING: [PATCH] PR target/67215: -fno-plt needs improvements for x86
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOrNKmQpsfXuvNOyevnpJq_muNmJCdvOYYKy6weEeFFi=Q at mail dot gmail dot com> <562F5E11 dot 1090503 at redhat dot com> <CAMe9rOqVM9Qhq1qPjo0qAVQFCWw-c+Ne2CtkpX_TcW5fcVbBuA at mail dot gmail dot com> <562F739F dot 2090000 at foss dot arm dot com> <CAMe9rOrL89kK=qxPS7n4e28+-3cpv_EdG0E0YT5uf3ppYNFamw at mail dot gmail dot com> <562F818A dot 90003 at foss dot arm dot com> <562F8B6F dot 7060605 at foss dot arm dot com> <CAMe9rOrOkzkY13Jja9VqNx536jqZZcuVYYaxOt6XcZGcP1gR+w at mail dot gmail dot com>
On 27/10/15 14:50, H.J. Lu wrote:
> On Tue, Oct 27, 2015 at 7:34 AM, Ramana Radhakrishnan
> <ramana.radhakrishnan@foss.arm.com> wrote:
>>
>>>
>>> OK, then it's fairly x86-64 specific optimization, because we can't do "call *mem" in
>>> aarch64 and some other targets.
>>
>> It is a fairly x86_64 specific optimization and doesn't apply to AArch64.
>>
>> The question really is what impact does removing the generic code handling have on aarch64 - is it a no-op or not for the existing -fno-plt implementation in the AArch64 backend ? The only case that is of interest is the bit below in calls.c and it looks like that may well be redundant with the logic in the backend already, but I have not done the full analysis to convince myself that the code in the backend is sufficient.
>>
>> - && (!flag_plt
>> - || lookup_attribute ("noplt", DECL_ATTRIBUTES (fndecl_or_type)))
>> - && !targetm.binds_local_p (fndecl_or_type))
>>
>
> -fno-plt is a backend specific optimization and should be handled
> in backend.
>
HJ, Thanks for committing the change even when we were discussing the change - As I suspected the handling in the backend isn't sufficient, the call expanders need to handle this case in the AArch64 backend. Minimally tested -
Ok if no regressions on aarch64-none-elf?
regards
Ramana
* config/aarch64/aarch64.md (call, call_value): Handle noplt.