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

[Timothy Arceri]

On Mon, 2015-11-02 at 03:27 -0500, Ilia Mirkin wrote:
> On Sun, Nov 1, 2015 at 3:33 AM, Timothy Arceri <t_arceri at yahoo.com.au>
> wrote:
> > Handles the case with function inout params where array elements
> > do an assignment to themselves e.g.
> > 
> >  void array_mod(inout int b[2])
> >  {
> >     b[0] = int(2);
> >     b[1] = b[1];
> >  }
> > 
> >  Fixes assert in nir for:
> >  ES31-CTS.arrays_of_arrays.InteractionFunctionCalls2
> > 
> > https://bugs.freedesktop.org/show_bug.cgi?id=92588
> > ---
> >  src/glsl/opt_copy_propagation_elements.cpp | 46
> > ++++++++++++++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> > 
> >  Piglit test: https://patchwork.freedesktop.org/patch/63355/
> > 
> > diff --git a/src/glsl/opt_copy_propagation_elements.cpp
> > b/src/glsl/opt_copy_propagation_elements.cpp
> > index 353a5c6..a62b625 100644
> > --- a/src/glsl/opt_copy_propagation_elements.cpp
> > +++ b/src/glsl/opt_copy_propagation_elements.cpp
> > @@ -439,6 +439,8 @@ ir_copy_propagation_elements_visitor::kill(kill_entry
> > *k)
> >  /**
> >   * Adds directly-copied channels between vector variables to the
> > available
> >   * copy propagation list.
> > + *
> > + * Also tidy up redundant function inout assignments while we are here.
> >   */
> >  void
> >  ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
> > @@ -450,6 +452,50 @@
> > ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
> >     if (ir->condition)
> >        return;
> > 
> > +   /* Handle a corner case with function inout params where array
> > elements
> > +    * do an assignment to themselves e.g.
> > +    *
> > +    * void array_mod(inout int b[2])
> > +    * {
> > +    *    b[0] = int(2);
> > +    *    b[1] = b[1];
> > +    * }
> 
> What if you have like
> 
> array_mod(inout vec2 b[2]) {
>   b[1] = b[1].xy;

This is handled by the change also. The swizzle will be removed before getting
here.

> or
>   b[1] = b[1].yx;

This will fail the first rhs_array->as_dereference_array() check (as it will
be a swizzle) so we will leave it alone as we should.

Just to be sure I wrote a couple of piglit tests and Cc'ed you in on them. 

> }
> 
> IOW, why is this case so special?
>
> > +    */
> > +   ir_rvalue *rhs_array = ir->rhs;
> > +   ir_rvalue *lhs_array = ir->lhs;
> > +   if (lhs_array->as_dereference_array() &&
> > +       rhs_array->as_dereference_array()) {
> > +      /* Check arrays are indexed by a const and match otherwise return
> > */
> > +      while (rhs_array->as_dereference_array() &&
> > +             lhs_array->as_dereference_array()) {
> > +
> > +         ir_dereference_array *rhs_deref_array =
> > +            rhs_array->as_dereference_array();
> > +         ir_dereference_array *lhs_deref_array =
> > +            lhs_array->as_dereference_array();
> > +
> > +         ir_constant *lhs_ai_const =
> > +            lhs_deref_array->array_index->as_constant();
> > +         ir_constant *rhs_ai_const =
> > +            rhs_deref_array->array_index->as_constant();
> > +         if (lhs_ai_const == NULL || rhs_ai_const == NULL ||
> > +             lhs_ai_const->value.i[0] != rhs_ai_const->value.i[0])
> > +            return;
> > +         lhs_array = lhs_deref_array->array;
> > +         rhs_array = rhs_deref_array->array;
> > +      }
> > +
> > +      ir_dereference_variable *lhs_var = lhs_array
> > ->as_dereference_variable();
> > +      ir_dereference_variable *rhs_var = rhs_array
> > ->as_dereference_variable();
> > +      if(lhs_var && rhs_var && lhs_var->var == rhs_var->var){
> 
> spaces please
> 
> > +        /* Removing the assignment now would mess up the loop iteration
> > +         * calling us.  Just flag it to not execute, and someone else
> > +         * will clean up the mess.
> > +         */
> > +        ir->condition = new(ralloc_parent(ir)) ir_constant(false);
> 
> I thought that the allocator was smart and you could just do new (ir)
> ir_constant(false). e.g.
> 
> src/glsl/lower_jumps.cpp:            new (ir) ir_constant(true)));

Yeah I think your right, this was a copy and paste from
opt_copy_propagation.cpp will chnage before pushing thanks.

> 
> > +      }
> > +   }
> > +
> >     ir_dereference_variable *lhs = ir->lhs->as_dereference_variable();
> >     if (!lhs || !(lhs->type->is_scalar() || lhs->type->is_vector()))
> >        return;
> > --
> > 2.4.3
> > 
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