[Mesa-dev] [PATCH 2/2] glsl: Don't copy propagate elements from SSBO or shared variables either

[Caio Marcelo de Oliveira Filho]

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com>


On Tue, Jun 12, 2018 at 03:48:14PM -0700, Ian Romanick wrote:
> From: Ian Romanick <ian.d.romanick at intel.com>
> 
> Since SSBOs can be written, copy propagating a read can cause the
> value to magically change.  SSBO reads are also very expensive, so
> doing it twice will be slower.
> 
> The same shader was helped by this patch and the previous.
> 
> Haswell, Broadwell, and Skylake had similar results. (Skylake shown)
> total instructions in shared programs: 14399119 -> 14399113 (<.01%)
> instructions in affected programs: 683 -> 677 (-0.88%)
> helped: 1
> HURT: 0
> 
> total cycles in shared programs: 532973113 -> 532971865 (<.01%)
> cycles in affected programs: 524666 -> 523418 (-0.24%)
> helped: 1
> HURT: 0
> 
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> Cc: mesa-stable at lists.freedesktop.org
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106774
> ---
>  src/compiler/glsl/opt_copy_propagation_elements.cpp | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/src/compiler/glsl/opt_copy_propagation_elements.cpp b/src/compiler/glsl/opt_copy_propagation_elements.cpp
> index 8bae424a1d0..8975e727522 100644
> --- a/src/compiler/glsl/opt_copy_propagation_elements.cpp
> +++ b/src/compiler/glsl/opt_copy_propagation_elements.cpp
> @@ -544,6 +544,10 @@ ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
>     if (!lhs || !(lhs->type->is_scalar() || lhs->type->is_vector()))
>        return;
>  
> +   if (lhs->var->data.mode == ir_var_shader_storage ||
> +       lhs->var->data.mode == ir_var_shader_shared)
> +      return;
> +
>     ir_dereference_variable *rhs = ir->rhs->as_dereference_variable();
>     if (!rhs) {
>        ir_swizzle *swiz = ir->rhs->as_swizzle();
> @@ -560,6 +564,10 @@ ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
>        orig_swizzle[3] = swiz->mask.w;
>     }
>  
> +   if (rhs->var->data.mode == ir_var_shader_storage ||
> +       rhs->var->data.mode == ir_var_shader_shared)
> +      return;
> +
>     /* Move the swizzle channels out to the positions they match in the
>      * destination.  We don't want to have to rewrite the swizzle[]
>      * array every time we clear a bit of the write_mask.
> -- 
> 2.14.4
> 
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