[Mesa-dev] [PATCH 08/10] glsl: fix new gcc6 warnings

[Ian Romanick]

On 02/16/2016 10:58 AM, Rob Clark wrote:
> src/compiler/glsl/lower_discard_flow.cpp:79:1: warning: ‘ir_visitor_status {anonymous}::lower_discard_flow_visitor::visit_enter(ir_loop_jump*)’ defined but not used [-Wunused-function]
>  lower_discard_flow_visitor::visit_enter(ir_loop_jump *ir)
>  ^~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Note, not sure if this was a latent bug?  Could be that was intended to
> override visit(ir_loop_jump *)?

I'll wager that is correct, and the bug has existed since day 1. :(

To hit the bug, you'd need a loop with both a discard and a continue.  I
suspect that is a rare combination.  To observe that the bug had been
hit, you'd have to use a derivative (either via dFdx() and friends or
texture()) in a particular way.  I'll have to try to think of a test case.

It might be easier to just add a unit test.  We know that

   for (int i = 0; i < x; i++) {
      if (z)
         continue;

      if (y)
         discard;
   }

should get transformed to

   for (int i = 0; i < x; i++) {
      if (z) {
         if (discarded)
            break;

         continue;
      }

      if (y) {
         discarded = true;
         discard;
      }

      if (discarded)
         break;
   }

> Signed-off-by: Rob Clark <robdclark at gmail.com>
> ---
>  src/compiler/glsl/lower_discard_flow.cpp | 12 ------------
>  1 file changed, 12 deletions(-)
> 
> diff --git a/src/compiler/glsl/lower_discard_flow.cpp b/src/compiler/glsl/lower_discard_flow.cpp
> index 9d0a56b..bdb96b4 100644
> --- a/src/compiler/glsl/lower_discard_flow.cpp
> +++ b/src/compiler/glsl/lower_discard_flow.cpp
> @@ -63,7 +63,6 @@ public:
>     }
>  
>     ir_visitor_status visit_enter(ir_discard *ir);
> -   ir_visitor_status visit_enter(ir_loop_jump *ir);
>     ir_visitor_status visit_enter(ir_loop *ir);
>     ir_visitor_status visit_enter(ir_function_signature *ir);
>  
> @@ -76,17 +75,6 @@ public:
>  } /* anonymous namespace */
>  
>  ir_visitor_status
> -lower_discard_flow_visitor::visit_enter(ir_loop_jump *ir)
> -{
> -   if (ir->mode != ir_loop_jump::jump_continue)
> -      return visit_continue;
> -
> -   ir->insert_before(generate_discard_break());
> -
> -   return visit_continue;
> -}
> -
> -ir_visitor_status
>  lower_discard_flow_visitor::visit_enter(ir_discard *ir)
>  {
>     ir_dereference *lhs = new(mem_ctx) ir_dereference_variable(discarded);
>