vtn: skip make-available/visible for shared

These barriers could prevent optimizations.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37417>

src/compiler/shader_enums.h

@@ -1058,6 +1058,9 @@ enum gl_access_qualifier
     * This means that the memory scope is the current device. It indicates
     * that reads and writes are coherent with reads and writes from other
     * shader invocations and other workgroups.
+    *
+    * This is not necessary for shared access. It is always workgroup
+    * coherent.
     */
    ACCESS_COHERENT      = (1 << 0),
 

src/compiler/spirv/spirv_to_nir.c

@@ -3140,6 +3140,18 @@ vtn_translate_scope(struct vtn_builder *b, SpvScope scope)
    }
 }
 
+static void
+optimize_barrier(nir_memory_semantics *semantics, nir_variable_mode *modes)
+{
+   nir_memory_semantics vis_avail = NIR_MEMORY_MAKE_AVAILABLE | NIR_MEMORY_MAKE_VISIBLE;
+
+   /* Shared access is always workgroup coherent in NIR. */
+   if (*modes == nir_var_mem_shared)
+      *semantics &= ~vis_avail;
+   if ((*semantics & vis_avail) == *semantics)
+      *modes &= ~nir_var_mem_shared;
+}
+
 static void
 vtn_emit_scoped_control_barrier(struct vtn_builder *b, SpvScope exec_scope,
                                 SpvScope mem_scope,
@@ -3150,6 +3162,8 @@ vtn_emit_scoped_control_barrier(struct vtn_builder *b, SpvScope exec_scope,
    nir_variable_mode modes = vtn_mem_semantics_to_nir_var_modes(b, semantics);
    mesa_scope nir_exec_scope = vtn_translate_scope(b, exec_scope);
 
+   optimize_barrier(&nir_semantics, &modes);
+
    /* Memory semantics is optional for OpControlBarrier. */
    mesa_scope nir_mem_scope;
    if (nir_semantics == 0 || modes == 0)
@@ -3157,6 +3171,9 @@ vtn_emit_scoped_control_barrier(struct vtn_builder *b, SpvScope exec_scope,
    else
       nir_mem_scope = vtn_translate_scope(b, mem_scope);
 
+   if (nir_mem_scope <= SCOPE_INVOCATION && nir_exec_scope <= SCOPE_INVOCATION)
+      return;
+
    nir_barrier(&b->nb, .execution_scope=nir_exec_scope, .memory_scope=nir_mem_scope,
                        .memory_semantics=nir_semantics, .memory_modes=modes);
 }
@@ -3169,6 +3186,8 @@ vtn_emit_memory_barrier(struct vtn_builder *b, SpvScope scope,
    nir_memory_semantics nir_semantics =
       vtn_mem_semantics_to_nir_mem_semantics(b, semantics);
 
+   optimize_barrier(&nir_semantics, &modes);
+
    /* No barrier to add. */
    if (nir_semantics == 0 || modes == 0)
       return;