Re: [PATCHv2 11/16] arch-armv7ve: add tune include for armv7ve and use it from cortexa7 and cortexa15

[Martin Jansa <martin.jansa@gmail.com>]

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On Wed, Nov 18, 2015 at 05:05:23PM +0000, Phil Blundell wrote:
> On Wed, 2015-11-18 at 17:51 +0100, Martin Jansa wrote:
> > On Wed, Nov 18, 2015 at 04:38:34PM +0000, Phil Blundell wrote:
> > > On Tue, 2015-11-17 at 11:58 +0100, Martin Jansa wrote:
> > > > * be aware that this -march value is available only in gcc-4.9
> > > > and
> > > >   newer:
> > > >   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57907
> > > > 
> > > 
> > > Can you clarify why this is an improvement?  The previous patch
> > > already
> > > changed cortex-a15.inc to use -mcpu=cortexa15, which effectively
> > > implies -march=armv7ve already (and works on all gcc versions) so
> > > I'm
> > > not entirely sure what this second patch really buys you.
> > 
> > Because -mcpu=cortexa15 and -march=armv7a conflict each other, so we
> > either have to stop putting -march in default CCARGS or at least set
> > compatible one like this patch does.
> 
> Ah right, got it.  I think it would be better to just stop passing 
> -march= in cases where we are using -mcpu=.  It seems a bit silly to
> create another huge maze of tune variables which all boil down to
> essentially a no-op.

The problem with this is that currently all the tunes are at least a bit
hierarchical, in this case

tune-cortexa15 was including
openembedded-core/meta/conf/machine/include/arm/arch-armv7a.inc

Which adds -march for anything with armv7a in TUNE_FEATURES:
TUNE_CCARGS .= "${@bb.utils.contains("TUNE_FEATURES", "armv7a", "-march=armv7-a", "", d)}"

and as bonus adds MACHINEOVERRIDES:
MACHINEOVERRIDES =. "${@bb.utils.contains("TUNE_FEATURES", "armv7a",
"armv7a:", "" ,d)}"

Then cortexa15 just uses tune features from "upper" tune-armv7a + just cortexa15, e.g.:

TUNE_FEATURES_tune-cortexa15 = "${TUNE_FEATURES_tune-armv7a} cortexa15"

So to get rid of -march we'll have to either

1) check in arch-armv7a.inc if TUNE_FEATURES also contains some TUNE_FEATURE which will append -mcpu
2) don't include armv7a TUNE_FEATURE in TUNE_FEATURES_tune-cortexa15t,
but the MACHINEOVERRIDES is still useful in many cases
3) use TUNE_CCARGS_remove to remove -march when adding -mcpu
4) rework whole tune files even more (probably by introducing another
variable which will hold just one of -march,-mcpu,-mtune and gets
appended to TUNE_CCARGS).

-- 
Martin 'JaMa' Jansa     jabber: Martin.Jansa@gmail.com

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