[Mesa-dev] [PATCH] glsl: remove logical xor FINISHME

[Kenneth Graunke]

On 01/09/2012 08:36 AM, Eric Anholt wrote:
> On Sun,  8 Jan 2012 22:44:17 -0500, Matt Turner<mattst88 at gmail.com>  wrote:
>> GLSL spec boneheadedly says (a ^^ a) must actually be evaluated.
>
> What it's trying to say there is that any side-effects of both LHS and
> RHS will occur (as opposed to how&&  or || work), not that you actually
> compute the expression that you could just avoid.  Any side effects will
> already be taken care of before opt_algebraic gets a look at the
> ir_expression.

In fact, with my patches that change ir_call to be a statement rather 
than an ir_rvalue, all expression trees are pure and there can be no 
side-effects.  I'm hoping to land those for Mesa 8.1.

Even now, though, there shouldn't be side-effects in expression trees. 
My patches just make it more explicit.

So I think it's actually safe to optimize a ^^ a == false.