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Re: Backend specific params.def? (Was Re: New parameters to control stringop expansion libcall strategy)
- From: Xinliang David Li <davidxl at google dot com>
- To: Jan Hubicka <hubicka at ucw dot cz>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Teresa Johnson <tejohnson at google dot com>
- Date: Sat, 3 Aug 2013 08:40:32 -0700
- Subject: Re: Backend specific params.def? (Was Re: New parameters to control stringop expansion libcall strategy)
- References: <CAAkRFZ+muGUjANkKqbp8r4HvddywmRgz+xPbVAUbuU9rE7pC7Q at mail dot gmail dot com> <20130803080650 dot GC18610 at kam dot mff dot cuni dot cz>
On Sat, Aug 3, 2013 at 1:06 AM, Jan Hubicka <firstname.lastname@example.org> wrote:
>> On x86_64, when the expected size of memcpy/memset is known (e.g, with
>> FDO), libcall strategy is used with the size is > 8192. This value is
>> hard coded, which makes it hard to do performance tuning. This patch
>> adds two new parameters to do that. Potential usage includes
>> per-application libcall strategy min-size tuning based on summary data
>> with FDO (e.g, instruction workset size).
>> Bootstrap and tested on x86_64/linux. Ok for trunk?
>> 2013-08-02 Xinliang David Li <email@example.com>
>> * params.def: New parameters.
>> * config/i386/i386.c (ix86_option_override_internal):
>> Override default libcall size limit with parameters.
> problem with this is that we introduce generic --param that is used only
> by x86 backend. I am not really guru on the command line options, but I think
> this is first time we try to do such thing. I wonder if
> 1) We want to introduce target specific params.def
We do have target specific tuning code for parameters though --
backend overrides the default value -- I think this is essentially
target specific params.
> 2) We want to use usual -msomething= options
> 3) We want to go this way?
I don't have strong opinion either way. To avoid controversy, let me
work on a -mxxx= version of the patch -- and hopefully it will be more