Mesa (master): nir: Two shared memory *blocks* may alias each other

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Module: Mesa
Branch: master
Commit: a9d230077f08955f97fddac84b4014d2131c8917
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=a9d230077f08955f97fddac84b4014d2131c8917

Author: Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com>
Date:   Tue Jul  7 17:38:03 2020 -0700

nir: Two shared memory *blocks* may alias each other

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Reviewed-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8699>

---

 src/compiler/nir/nir_deref.c                 | 12 ++++++++++++
 src/compiler/nir/nir_remove_dead_variables.c | 12 ++++++++++--
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/compiler/nir/nir_deref.c b/src/compiler/nir/nir_deref.c
index 4735175b786..f406c87bbbf 100644
--- a/src/compiler/nir/nir_deref.c
+++ b/src/compiler/nir/nir_deref.c
@@ -492,6 +492,18 @@ nir_compare_deref_paths(nir_deref_path *a_path,
              deref_path_contains_coherent_decoration(b_path))
             return nir_derefs_may_alias_bit;
 
+         /* Per SPV_KHR_workgroup_memory_explicit_layout and GL_EXT_shared_memory_block,
+          * shared blocks alias each other.
+          */
+         if (a_path->path[0]->modes & nir_var_mem_shared &&
+             b_path->path[0]->modes & nir_var_mem_shared &&
+             (glsl_type_is_interface(a_path->path[0]->var->type) ||
+              glsl_type_is_interface(b_path->path[0]->var->type))) {
+            assert(glsl_type_is_interface(a_path->path[0]->var->type) &&
+                   glsl_type_is_interface(b_path->path[0]->var->type));
+            return nir_derefs_may_alias_bit;
+         }
+
          /* If we can chase the deref all the way back to the variable and
           * they're not the same variable and at least one is not declared
           * coherent, we know they can't possibly alias.
diff --git a/src/compiler/nir/nir_remove_dead_variables.c b/src/compiler/nir/nir_remove_dead_variables.c
index 19e56d077d4..0182c9889ed 100644
--- a/src/compiler/nir/nir_remove_dead_variables.c
+++ b/src/compiler/nir/nir_remove_dead_variables.c
@@ -71,8 +71,16 @@ add_var_use_deref(nir_deref_instr *deref, struct set *live)
     * make them live.  Only keep them if they are used by some intrinsic.
     */
    if ((deref->var->data.mode & (nir_var_function_temp |
-                                 nir_var_shader_temp |
-                                 nir_var_mem_shared)) &&
+                                 nir_var_shader_temp)) &&
+       !deref_used_for_not_store(deref))
+      return;
+
+   /*
+    * Shared memory blocks (interface type) alias each other, so be
+    * conservative in that case.
+    */
+   if ((deref->var->data.mode & nir_var_mem_shared) &&
+       !glsl_type_is_interface(deref->var->type) &&
        !deref_used_for_not_store(deref))
       return;