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Re: [PATCH] Add explicit VIS intrinsics for addition and subtraction.
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: Vladimir Makarov <vmakarov at redhat dot com>
- Cc: David Miller <davem at davemloft dot net>, gcc-patches at gcc dot gnu dot org
- Date: Sat, 15 Oct 2011 16:41:09 +0200
- Subject: Re: [PATCH] Add explicit VIS intrinsics for addition and subtraction.
- References: <20110927.000118.1421173401433924103.davem@davemloft.net> <201109290038.49451.ebotcazou@adacore.com> <4E984BD8.50408@redhat.com>
> About the 1st question. Before gcc4.7, the only class (allocno class)
> used for coloring can be a cover class. So it was not possible to use
> GENERAL_OR_EXTRA_FP_REGS in gcc4.6 and older versions. Starting gcc4.7,
> class used for coloring can be any class which is more profitable than
> memory. Although there is inaccuracy in cost calculations for -O1
> because only one pass for cost calculations is used (it is very
> expensive pass). To get better cost evaluations, more passes should be
> used. But again we don't do more 2 passes because even one pass is not
> cheap.
>
> In brief, I don't see any criminal that the class calculation is
> different for -O1 and -O2.
Fine with me. I'm going to apply the above patchlet then.
> About the 2nd question. It seems to me wrong. I'd remove function
> process_bb_node_for_hard_reg_moves and its call from
> setup_allocno_cover_class_and_costs because function
> process_regs_for_copy is more accurate (it works with subreg).
> Although, I might be miss something here. There were a lot of problems
> and tunings of cost calculation code. Generated code *performance* (and
> even generation of *valid* code) is very sensitive to changes in
> ira-costs.c. So even if such change looks obvious, a lot of testing and
> benchmarking should be done. I could do that but it will take a week or
> two before committing such change if everything is ok.
Understood. I essentially wanted to bring this to your attention, since it
looked like a small oddity to me. This might be something to play with for
future improvements, but it's your call of course.
Thanks for the detailed answer.
--
Eric Botcazou