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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Forcing GNAT to use 32-bit load/store instructions on ARM?
Date: Fri, 11 Jul 2014 19:05:24 +0100
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Date: 2014-07-11T19:05:24+01:00
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Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> writes:

> On 2014-07-10, Simon Wright <simon@pushface.org> wrote:
>> Simon Wright <simon@pushface.org> writes:
>>
>>> The x86_64 code accesses all 32 bits of V. If it is more efficient on
>>> arm to access the relevant bytes for the component assignments, I
>>> expect that's what would happen (as reported).
>>
>> Just tried this on Raspberry Pi (GCC 4.6.3): yes, it only accesses the
>> relevant bytes.
>
> Just to make sure: you mean it uses ldrb/strb instead of ldr/str
> in the generated code ?

Yes. I don't understand all the asm, but that part is clear!

_ada_atom:
	@ args = 0, pretend = 0, frame = 0
	@ frame_needed = 0, uses_anonymous_args = 0
	@ link register save eliminated.
	ldr	r2, .L2
	ldr	r3, .L2+4
	ldmia	r2, {r1, r2}
	str	r1, [r3, #0]
	ldrb	r1, [r3, #0]	@ zero_extendqisi2
	bic	r1, r1, #1
	strb	r1, [r3, #0]
	ldrb	r1, [r3, #3]	@ zero_extendqisi2
	bic	r1, r1, #128
	strb	r1, [r3, #3]
	str	r2, [r3, #0]
	bx	lr