Re: [PING][PATCH v3] Disable reg offset in quad-word store for Falkor

[Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>]

Hi Siddhesh,

I still don't like the idea of disabling a whole class of instructions in the md file.
It seems much better to adjust the costs here so that you get most of the
improvement now, and fine tune it once we can differentiate between
loads and stores.

Taking your example, adding -funroll-loops generates this for Falkor:

	ldr	q7, [x2, x18]
	add	x5, x18, 16
	add	x4, x1, x18
	add	x10, x18, 32
	add	x11, x1, x5
	add	x3, x18, 48
	add	x12, x1, x10
	add	x9, x18, 64
	add	x14, x1, x3
	add	x8, x18, 80
	add	x15, x1, x9
	add	x7, x18, 96
	add	x16, x1, x8
	str	q7, [x4]
	ldr	q16, [x2, x5]
	add	x6, x18, 112
	add	x17, x1, x7
	add	x18, x18, 128
	add	x5, x1, x6
	cmp	x18, x13
	str	q16, [x11]
	ldr	q17, [x2, x10]
	str	q17, [x12]
	ldr	q18, [x2, x3]
	str	q18, [x14]
	ldr	q19, [x2, x9]
	str	q19, [x15]
	ldr	q20, [x2, x8]
	str	q20, [x16]
	ldr	q21, [x2, x7]
	str	q21, [x17]
	ldr	q22, [x2, x6]
	str	q22, [x5]
	bne	.L25

If you adjust costs however you'd get this:

.L25:
	ldr	q7, [x14]
	add	x14, x14, 128
	add	x4, x4, 128
	str	q7, [x4, -128]
	ldr	q16, [x14, -112]
	str	q16, [x4, -112]
	ldr	q17, [x14, -96]
	str	q17, [x4, -96]
	ldr	q18, [x14, -80]
	str	q18, [x4, -80]
	ldr	q19, [x14, -64]
	str	q19, [x4, -64]
	ldr	q20, [x14, -48]
	str	q20, [x4, -48]
	ldr	q21, [x14, -32]
	str	q21, [x4, -32]
	ldr	q22, [x14, -16]
	cmp	x14, x9
	str	q22, [x4, -16]
	bne	.L25

So it seems to me using existing cost mechanisms is always preferable, even if you
currently can't differentiate between loads and stores.

Wilco