[Mesa-dev] [PATCH 48/61] spirv: Make push constants an offset-based pointer

[Jason Ekstrand]

Push constants have been a weird edge-case for a while in that they have
explitic offsets but we've been internally building access chains for
them.  This mostly works but it means that passing pointers to push
constants through as function arguments is broken.  The easy thing to do
for now is to just treat them like UBOs or SSBOs only without a block
index.  This does loose a bit of information since we no longer have an
accurate access range and any indirect access will look like it could
read the whole block.  Unfortunately, there's not much we can do about
that.  Once NIR derefs get a bit more powerful, we can plumb these
through as derefs and be able to reason about them again.
---
 src/compiler/spirv/spirv_to_nir.c  |  7 +++++++
 src/compiler/spirv/vtn_variables.c | 38 ++++++++++----------------------------
 2 files changed, 17 insertions(+), 28 deletions(-)

diff --git a/src/compiler/spirv/spirv_to_nir.c b/src/compiler/spirv/spirv_to_nir.c
index 29b4512..06368df 100644
--- a/src/compiler/spirv/spirv_to_nir.c
+++ b/src/compiler/spirv/spirv_to_nir.c
@@ -1168,6 +1168,13 @@ vtn_handle_type(struct vtn_builder *b, SpvOp opcode,
          val->type->type = glsl_vector_type(GLSL_TYPE_UINT, 2);
       }
 
+      if (storage_class == SpvStorageClassPushConstant) {
+         /* These can actually be stored to nir_variables and used as SSA
+          * values so they need a real glsl_type.
+          */
+         val->type->type = glsl_uint_type();
+      }
+
       if (storage_class == SpvStorageClassWorkgroup &&
           b->options->lower_workgroup_access_to_offsets) {
          uint32_t size, align;
diff --git a/src/compiler/spirv/vtn_variables.c b/src/compiler/spirv/vtn_variables.c
index 49cb837..944c1ab 100644
--- a/src/compiler/spirv/vtn_variables.c
+++ b/src/compiler/spirv/vtn_variables.c
@@ -64,6 +64,7 @@ vtn_pointer_uses_ssa_offset(struct vtn_builder *b,
 {
    return ptr->mode == vtn_variable_mode_ubo ||
           ptr->mode == vtn_variable_mode_ssbo ||
+          ptr->mode == vtn_variable_mode_push_constant ||
           (ptr->mode == vtn_variable_mode_workgroup &&
            b->options->lower_workgroup_access_to_offsets);
 }
@@ -269,6 +270,12 @@ vtn_ssa_offset_pointer_dereference(struct vtn_builder *b,
          }
 
          offset = nir_imm_int(&b->nb, base->var->shared_location);
+      } else if (base->mode == vtn_variable_mode_push_constant) {
+         /* Push constants neither need nor have a block index */
+         vtn_assert(!block_index);
+
+         /* Start off with at the start of the push constant block. */
+         offset = nir_imm_int(&b->nb, 0);
       } else {
          /* The code above should have ensured a block_index when needed. */
          vtn_assert(block_index);
@@ -662,31 +669,6 @@ vtn_type_block_size(struct vtn_builder *b, struct vtn_type *type)
 }
 
 static void
-vtn_access_chain_get_offset_size(struct vtn_builder *b,
-                                 struct vtn_access_chain *chain,
-                                 struct vtn_type *type,
-                                 unsigned *access_offset,
-                                 unsigned *access_size)
-{
-   *access_offset = 0;
-
-   for (unsigned i = 0; i < chain->length; i++) {
-      if (chain->link[i].mode != vtn_access_mode_literal)
-         break;
-
-      if (glsl_type_is_struct(type->type)) {
-         *access_offset += type->offsets[chain->link[i].id];
-         type = type->members[chain->link[i].id];
-      } else {
-         *access_offset += type->stride * chain->link[i].id;
-         type = type->array_element;
-      }
-   }
-
-   *access_size = vtn_type_block_size(b, type);
-}
-
-static void
 _vtn_load_store_tail(struct vtn_builder *b, nir_intrinsic_op op, bool load,
                      nir_ssa_def *index, nir_ssa_def *offset,
                      unsigned access_offset, unsigned access_size,
@@ -882,8 +864,7 @@ vtn_block_load(struct vtn_builder *b, struct vtn_pointer *src)
       break;
    case vtn_variable_mode_push_constant:
       op = nir_intrinsic_load_push_constant;
-      vtn_access_chain_get_offset_size(b, src->chain, src->var->type,
-                                       &access_offset, &access_size);
+      access_size = b->shader->num_uniforms;
       break;
    case vtn_variable_mode_workgroup:
       op = nir_intrinsic_load_shared;
@@ -1657,7 +1638,8 @@ vtn_pointer_from_ssa(struct vtn_builder *b, nir_ssa_def *ssa,
       ptr->offset = nir_channel(&b->nb, ssa, 1);
    } else {
       vtn_assert(ssa->num_components == 1);
-      vtn_assert(ptr->mode == vtn_variable_mode_workgroup);
+      vtn_assert(ptr->mode == vtn_variable_mode_workgroup ||
+                 ptr->mode == vtn_variable_mode_push_constant);
       ptr->block_index = NULL;
       ptr->offset = ssa;
    }
-- 
2.5.0.400.gff86faf