Mesa (master): gallium + mesa/st: Add PIPE_CAP_NIR_ATOMICS_AS_DEREF and use it

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Module: Mesa
Branch: master
Commit: a03e24aa7faafe2dca77150e709727d4276b08cb
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=a03e24aa7faafe2dca77150e709727d4276b08cb

Author: Gert Wollny <gert.wollny at collabora.com>
Date:   Sat Jun 27 22:40:56 2020 +0200

gallium + mesa/st: Add PIPE_CAP_NIR_ATOMICS_AS_DEREF and use it

This cap is useful for drivers that support hardware atomics and need
special handling to resolve their addresses.

Signed-off-by: Gert Wollny <gert.wollny at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6025>

---

 docs/gallium/screen.rst                   | 1 +
 src/gallium/auxiliary/util/u_screen.c     | 1 +
 src/gallium/include/pipe/p_defines.h      | 1 +
 src/mesa/state_tracker/st_glsl_to_nir.cpp | 7 +++++--
 4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/docs/gallium/screen.rst b/docs/gallium/screen.rst
index 2f0b4bf0d88..45c82802cc9 100644
--- a/docs/gallium/screen.rst
+++ b/docs/gallium/screen.rst
@@ -589,6 +589,7 @@ The integer capabilities:
 * ``PIPE_CAP_MAP_UNSYNCHRONIZED_THREAD_SAFE``: Whether mapping a buffer as unsynchronized from any thread is safe.
 * ``PIPE_CAP_GLSL_ZERO_INIT``: Choose a default zero initialization some glsl variables. If `1`, then all glsl shader variables and gl_FragColor are initialized to zero. If `2`, then shader out variables are not initialized but function out variables are.
 * ``PIPE_CAP_BLEND_EQUATION_ADVANCED``: Driver supports blend equation advanced without necessarily supporting FBFETCH.
+* ``PIPE_CAP_NIR_ATOMICS_AS_DEREF``: Whether NIR atomics instructions should reference atomics as NIR derefs instead of by indices.
 
 .. _pipe_capf:
 
diff --git a/src/gallium/auxiliary/util/u_screen.c b/src/gallium/auxiliary/util/u_screen.c
index ccf2fa8c75d..9f174c58701 100644
--- a/src/gallium/auxiliary/util/u_screen.c
+++ b/src/gallium/auxiliary/util/u_screen.c
@@ -294,6 +294,7 @@ u_pipe_screen_get_param_defaults(struct pipe_screen *pscreen,
    case PIPE_CAP_TGSI_TES_LAYER_VIEWPORT:
    case PIPE_CAP_CAN_BIND_CONST_BUFFER_AS_VERTEX:
    case PIPE_CAP_TGSI_DIV:
+   case PIPE_CAP_NIR_ATOMICS_AS_DEREF:
       return 0;
 
    case PIPE_CAP_ALLOW_MAPPED_BUFFERS_DURING_EXECUTION:
diff --git a/src/gallium/include/pipe/p_defines.h b/src/gallium/include/pipe/p_defines.h
index ddeac139f93..d82ffcd14dc 100644
--- a/src/gallium/include/pipe/p_defines.h
+++ b/src/gallium/include/pipe/p_defines.h
@@ -954,6 +954,7 @@ enum pipe_cap
    PIPE_CAP_MAP_UNSYNCHRONIZED_THREAD_SAFE,
    PIPE_CAP_GLSL_ZERO_INIT,
    PIPE_CAP_BLEND_EQUATION_ADVANCED,
+   PIPE_CAP_NIR_ATOMICS_AS_DEREF,
 };
 
 /**
diff --git a/src/mesa/state_tracker/st_glsl_to_nir.cpp b/src/mesa/state_tracker/st_glsl_to_nir.cpp
index 17237a62091..99bbbef79db 100644
--- a/src/mesa/state_tracker/st_glsl_to_nir.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_nir.cpp
@@ -432,6 +432,7 @@ st_glsl_to_nir_post_opts(struct st_context *st, struct gl_program *prog,
                          struct gl_shader_program *shader_program)
 {
    nir_shader *nir = prog->nir;
+   struct pipe_screen *screen = st->pipe->screen;
 
    /* Make a pass over the IR to add state references for any built-in
     * uniforms that are used.  This has to be done now (during linking).
@@ -486,7 +487,9 @@ st_glsl_to_nir_post_opts(struct st_context *st, struct gl_program *prog,
        !st->ctx->Const.PackedDriverUniformStorage)
       NIR_PASS_V(nir, st_nir_lower_builtin);
 
-   NIR_PASS_V(nir, gl_nir_lower_atomics, shader_program, true);
+   if (!screen->get_param(screen, PIPE_CAP_NIR_ATOMICS_AS_DEREF))
+      NIR_PASS_V(nir, gl_nir_lower_atomics, shader_program, true);
+
    NIR_PASS_V(nir, nir_opt_intrinsics);
 
    /* Lower 64-bit ops. */
@@ -508,7 +511,7 @@ st_glsl_to_nir_post_opts(struct st_context *st, struct gl_program *prog,
       (nir_var_shader_in | nir_var_shader_out | nir_var_function_temp );
    nir_remove_dead_variables(nir, mask, NULL);
 
-   if (!st->has_hw_atomics)
+   if (!st->has_hw_atomics && !screen->get_param(screen, PIPE_CAP_NIR_ATOMICS_AS_DEREF))
       NIR_PASS_V(nir, nir_lower_atomics_to_ssbo);
 
    st_finalize_nir_before_variants(nir);