[Mesa-dev] [PATCH] glsl: remove redundant function inout assignments

[Timothy Arceri]

On Tue, 2015-11-03 at 19:39 -0500, Ilia Mirkin wrote:
> On Tue, Nov 3, 2015 at 7:31 PM, Timothy Arceri <t_arceri at yahoo.com.au>
> wrote:
> > On Tue, 2015-11-03 at 19:21 -0500, Ilia Mirkin wrote:
> > > I'm still unclear what problem you're trying to solve here? What's
> > > wrong with having b[1] = b[1]?
> > 
> > There is nothing wrong with it, but nir seems to expect this type of
> > assignment to be optimised out and hits an assert if its not. Its removed
> > for
> > non arrays in opt_copy_propagation.cpp see add_copy()
> 
> Sounds like a bugfix for nir might be in order then? What if you have,
> say, b[1] = b[1] + 0 and then NIR optimizes away the + 0? Or +
> some_var which happens to become 0 as a result of optimizations?

Assuming the GLSL IR doesn't get to it first your right, however this is
tripping up nir_lower_vars_to_ssa() which is the first optimisation call for
nir drivers, so we still need to add this to the GLSL IR optimisations unless
there is an argument to move the lower pass until after the other optimisation
passes but I assume it was added to the beginning for a reason.

I moved the lower call to the end of the optimisation list to see what happens
and it does indeed still fail. I can have a go at adding the optimisation to
nir when I get some time but I don't think this should be a blocker to the
GLSL IR fix.

Tim


> 
>   -ilia
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