Re: [RFC PATCH, i386]: Allow zero_extended addresses (+ problems with reload and offsetable address, "o" constraint)

[Uros Bizjak <ubizjak at gmail dot com>]

On Mon, Aug 8, 2011 at 5:30 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
> Uros Bizjak wrote:
>
>> Although, it would be nice for reload to subsequently fix CSE'd
>> non-offsetable memory by copying address to temporary reg (*as said in
>> the documentation*), we could simply require an XMM temporary for
>> TImode reloads to/from integer registers, and this fixes ICE for x32.
>
> Moves are special as far as reload is concerned. ?If there is already
> a move instruction present *before* reload, it will get fixed up
> according to its constraints as any other instruction.
>
> However, reload will *introduce* new moves as part of its operation,
> and those will *not* themselves get reloaded. ?Instead, reload simply
> assumes that every plain move will just succeed without requiring
> any reload; if this is not true, the target *must* provide a
> secondary reload for this move.
>
> (Note that the secondary reload could also work by reloading the
> target address into a temporary; that's up to the target to
> implement.)

Whoa, indeed.

Using attached patch that reloads memory address instead of going
through XMM register, the code for the testcase improves from:

test:
.LFB0:
	.cfi_startproc
	pushq	%rbx
	.cfi_def_cfa_offset 16
	.cfi_offset 3, -16
	sall	$4, %esi
	addl	%edi, %esi
	movdqa	(%esi), %xmm0
	movdqa	%xmm0, -16(%rsp)
	movq	-16(%rsp), %rcx
	movq	-8(%rsp), %rbx
	addq	$1, %rcx
	adcq	$0, %rbx
	movq	%rcx, -16(%rsp)
	sall	$4, %edx
	movq	%rbx, -8(%rsp)
	movdqa	-16(%rsp), %xmm0
	movdqa	%xmm0, (%esi)
	pxor	%xmm0, %xmm0
	movdqa	%xmm0, (%edx,%esi)
	popq	%rbx
	.cfi_def_cfa_offset 8
	ret

to:

test:
.LFB0:
	.cfi_startproc
	sall	$4, %esi
	pushq	%rbx
	.cfi_def_cfa_offset 16
	.cfi_offset 3, -16
	addl	%edi, %esi
	pxor	%xmm0, %xmm0
	mov	%esi, %eax
	movq	(%rax), %rcx
	movq	8(%rax), %rbx
	addq	$1, %rcx
	adcq	$0, %rbx
	sall	$4, %edx
	movq	%rcx, (%rax)
	movq	%rbx, 8(%rax)
	movdqa	%xmm0, (%edx,%esi)
	popq	%rbx
	.cfi_def_cfa_offset 8
	ret

H.J., can you please test attached patch? This optimization won't
trigger on x86_64 anymore.

Thanks,
Uros.

Attachment: z.diff.txt
Description: Text document