glsl: Don't lower vector derefs for SSBOs, UBOs, and shared

All of these are backed by some sort of memory so if you have multiple
threads writing to different components of the same vector at the same
time, the load-vec-store pattern that GLSL IR emits won't work.  This
shouldn't affect any drivers today as they all call GLSL IR lowering
which lowers access to these variables to index+offset intrinsics before
we get to this point.  However, NIR will start handling the derefs
itself and won't want the lowering.

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

diff --git a/src/compiler/glsl/lower_vector_derefs.cpp b/src/compiler/glsl/lower_vector_derefs.cpp
index 2aae30d8201101d2c4afcf6ce4a632aad3eda02a..0c09630fa0301b3f9f8949a37b92a91bf35767d3 100644 (file)
--- a/src/compiler/glsl/lower_vector_derefs.cpp
+++ b/src/compiler/glsl/lower_vector_derefs.cpp
@@ -63,6 +63,16 @@ vector_deref_visitor::visit_enter(ir_assignment *ir)
    if (!deref->array->type->is_vector())
       return ir_rvalue_enter_visitor::visit_enter(ir);
 
+   /* SSBOs and shared variables are backed by memory and may be accessed by
+    * multiple threads simultaneously.  It's not safe to lower a single
+    * component store to a load-vec-store because it may race with writes to
+    * other components.
+    */
+   ir_variable *var = deref->variable_referenced();
+   if (var->data.mode == ir_var_shader_storage ||
+       var->data.mode == ir_var_shader_shared)
+      return ir_rvalue_enter_visitor::visit_enter(ir);
+
    ir_rvalue *const new_lhs = deref->array;
 
    void *mem_ctx = ralloc_parent(ir);
@@ -150,6 +160,17 @@ vector_deref_visitor::handle_rvalue(ir_rvalue **rv)
    if (!deref->array->type->is_vector())
       return;
 
+   /* Back-ends need to be able to handle derefs on vectors for SSBOs, UBOs,
+    * and shared variables.  They have to handle it for writes anyway so we
+    * may as well require it for reads.
+    */
+   ir_variable *var = deref->variable_referenced();
+   if (var && (var->data.mode == ir_var_shader_storage ||
+               var->data.mode == ir_var_shader_shared ||
+               (var->data.mode == ir_var_uniform &&
+                var->get_interface_type())))
+      return;
+
    void *mem_ctx = ralloc_parent(deref);
    *rv = new(mem_ctx) ir_expression(ir_binop_vector_extract,
                                     deref->array,