[Mesa-dev] [PATCH 2/4] i965/fs: Disable CSE on instructions writing to HW_REG.

[Eric Anholt]

Matt Turner <mattst88 at gmail.com> writes:

> CSE would otherwise combine the two mul(8) emitted by [iu]mulExtended:
>
> 	mul(8)  acc0 x y
> 	mach(8) null x y
> 	mov(8)  lsb  acc0
> 	...
> 	mul(8)  acc0 x y
> 	mach(8) msb  x y
> Into:
> 	mul(8)  temp x y
> 	mov(8)  acc0 temp
> 	mach(8) null x y
> 	mov(8)  lsb  acc0
> 	...
> 	mov(8)  acc0 temp
> 	mach(8) msb  x y
>
> But mul(8) into the accumulator produces more than 32-bits of precision,
> which is required and lost if multiplying into a general register and
> moving to the accumulator.

I tried to come up with a case that we wanted CSE on a general register
description instead of our abstract files, and couldn't come up with
any.

These two (2/4, 3/4) are:

Reviewed-by: Eric Anholt <eric at anholt.net>
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