[PATCH][GCC][mid-end] Allow larger copies when target supports unaligned access [Patch (1/2)]

[Richard Biener]

On Tue, 14 Nov 2017, Tamar Christina wrote:

> Hi All,
> 
> This patch allows larger bitsizes to be used as copy size
> when the target does not have SLOW_UNALIGNED_ACCESS.
> 
> fun3:
> 	adrp	x2, .LANCHOR0
> 	add	x2, x2, :lo12:.LANCHOR0
> 	mov	x0, 0
> 	sub	sp, sp, #16
> 	ldrh	w1, [x2, 16]
> 	ldrb	w2, [x2, 18]
> 	add	sp, sp, 16
> 	bfi	x0, x1, 0, 8
> 	ubfx	x1, x1, 8, 8
> 	bfi	x0, x1, 8, 8
> 	bfi	x0, x2, 16, 8
> 	ret
> 
> is turned into
> 
> fun3:
> 	adrp	x0, .LANCHOR0
> 	add	x0, x0, :lo12:.LANCHOR0
> 	sub	sp, sp, #16
> 	ldrh	w1, [x0, 16]
> 	ldrb	w0, [x0, 18]
> 	strh	w1, [sp, 8]
> 	strb	w0, [sp, 10]
> 	ldr	w0, [sp, 8]
> 	add	sp, sp, 16
> 	ret
> 
> which avoids the bfi's for a simple 3 byte struct copy.
> 
> Regression tested on aarch64-none-linux-gnu and x86_64-pc-linux-gnu and no regressions.
> 
> This patch is just splitting off from the previous combined patch with AArch64 and adding
> a testcase.
> 
> I assume Jeff's ACK from https://gcc.gnu.org/ml/gcc-patches/2017-08/msg01523.html is still
> valid as the code did not change.

Given your no_slow_unalign isn't mode specific can't you use the existing
non_strict_align?

Otherwise the expr.c change looks ok.

Thanks,
Richard.

> Thanks,
> Tamar
> 
> 
> gcc/
> 2017-11-14  Tamar Christina  <tamar.christina@arm.com>
> 
> 	* expr.c (copy_blkmode_to_reg): Fix bitsize for targets
> 	with fast unaligned access.
> 	* doc/sourcebuild.texi (no_slow_unalign): New.
> 	
> gcc/testsuite/
> 2017-11-14  Tamar Christina  <tamar.christina@arm.com>
> 
> 	* gcc.dg/struct-simple.c: New.
> 	* lib/target-supports.exp
> 	(check_effective_target_no_slow_unalign): New.
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)