[Mesa-dev] [RFC] i965/dbg: Expose cases hitting a presumably dead optimization

[Jason Ekstrand]

On Fri, Mar 11, 2016 at 4:40 AM, Topi Pohjolainen <
topi.pohjolainen at intel.com> wrote:

> The logic iterates over param[] which contains pointers to
> uniform storage set during linking (see
> link_assign_uniform_locations()).
>
> The pointers are unique and it should be impossible to find
> matching entries.
>
> I couldn't find any regressions with test system. In addition
> I tried several benchmarks on HSW and none hit this.
>
> I'm hoping to remove this optimization attempt. This is the only
> bit that depends on knowing about the actual storage during
> compilation. All the rest deal with just relative push and pull
> locations once the actual filling of pull_param[] is moved
> outside the compiler just as param[]. (Filling pull_param is
> based on the pull locations and doesn't need to be inside the
> compiler).
>
> Any thoughts?
>

I'm not 100% sure what you're trying to do, but I have a branch that may be
of interest:

https://cgit.freedesktop.org/~jekstrand/mesa/log/?h=wip/i965-uniforms

The branch enables support for pushing small uniform arrays.  Among other
things, it redoes the way we do push constants and gets rid of some of the
data tracking in the backend compiler.  The big reason why I haven't tried
too hard to get it merged is because it regresses Sandy Bridge just a bit.
I know I've seen and fixed the bug before in an alternate attempt, but I
don't remember how.

I'm going to be refreshing it soon because we need indirect push constants
for the Vulkan driver.  (The branch is already merged into the Vulkan
branch.)

--Jason


> Signed-off-by: Topi Pohjolainen <topi.pohjolainen at intel.com>
> CC: Ian Romanick <ian.d.romanick at intel.com>
> CC: Kenneth Graunke <kenneth at whitecape.org>
> CC: Eric Anholt <eric at anholt.net>
> ---
>  src/mesa/drivers/dri/i965/brw_vec4.cpp | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp
> b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> index cf62ed9..bb62fef 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> @@ -774,6 +774,8 @@ vec4_visitor::move_push_constants_to_pull_constants()
>             }
>
>             if (matches == 4) {
> +               unreachable("Values in param[] are unique, match is
> impossible");
> +               exit(1);
>                pull_constant_loc[i / 4] = j / 4;
>                break;
>             }
> --
> 2.5.0
>
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