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Re: [Patchv2 3/4] Control SRA and IPA-SRA by a param rather than MOVE_RATIO
- From: James Greenhalgh <james dot greenhalgh at arm dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Richard Earnshaw <Richard dot Earnshaw at arm dot com>, Marcus Shawcroft <Marcus dot Shawcroft at arm dot com>, Andrew Pinski <pinskia at gmail dot com>
- Date: Wed, 1 Oct 2014 17:38:12 +0100
- Subject: Re: [Patchv2 3/4] Control SRA and IPA-SRA by a param rather than MOVE_RATIO
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On Fri, Sep 26, 2014 at 10:11:13AM +0100, Richard Biener wrote:
> On Thu, Sep 25, 2014 at 4:57 PM, James Greenhalgh
> <firstname.lastname@example.org> wrote:
> Given the special value to note the default for the new --params is
> zero a user cannot disable scalarization that way.
> I still somehow dislike that you need a target hook to compute the
> default. Why doesn't it work to do, in opts.c:default_options_optimization
> get_move_ratio (speed_p) * MOVE_MAX_PIECES,
> opts->x_param_values, opts_set->x_param_values);
> and override that default in targets option_override hook the same way?
The problem I am having is getting "get_move_ratio" right, without breaking
the modular design.
default_options_optimization, and the rest of opts.c is going to end up in
libcommon-target.a, so we are not going to have access to any
An early draft of this patch used the MOVE_RATIO macro to set the default
value. This worked fine for AArch64 and ARM targets (which both use a
simple C expression for MOVE_RATIO), but failed for x86_64 which defines
MOVE_RATIO as so:
#define MOVE_RATIO(speed) ((speed) ? ix86_cost->move_ratio : 3)
Dealing with that ix86_cost symbol is what causes us the pain.
It seems reasonable that a target might want to define MOVE_RATIO
as some function of their tuning parameters, so I don't want to
disallow that usage.
This inspired me to try turning this in to a target hook, but this
doesn't help as opts.c only gets access to common-target.def target
hooks. These suffer the same problem, they don't have access to any
I suppose I could port any target with a definition of MOVE_RATIO to
override the default parameter value in their option overriding code,
but that makes this a very large patch set (many targets define
Is this an avenue worth exploring? I agree the very special target
hook is not ideal.