[Mesa-dev] [PATCH] glsl: Remove CSE pass.

[Matt Turner]

On Sat, Oct 3, 2015 at 11:31 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Sat, Oct 3, 2015 at 1:57 PM, Matt Turner <mattst88 at gmail.com> wrote:
>> With NIR, it actually hurts things.
>
> Buuutt.... not everything uses NIR.

Well...

> Of course I'm sure it has a
> similarly negative effect with nouveau/codegen, but I'm not so sure
> about things like nv30 which don't have an optimizing compiler
> backend. IMHO there should be a bit somewhere in the compiler options
> that indicates whether the driver implements an optimizing compiler,
> and if so, then all these idiotic optimizations should be removed. [I
> realize some are needed for correctness, obviously keep those.]

They're not idiotic. They all serve(d) some useful purpose. To say
they're idiotic is insulting to the authors.

Anyway, the GLSL IR CSE pass was added (commit fd05ede0d0) for a
single purpose: to fix a performance regression in a broken benchmark
on i965 after some changes to i965's instruction scheduler. It no
longer serves that purpose.

If anything else accidentally benefited from it, they'll simply go
back to the [acceptable] way they were.