dawn_wire: use memcpy on structures when possible

This patch sets 'is_wire_transparent' on the structures whose members
are all wire transparent and are not pointers, so that we can use
memcpy when serializing and deserializing these structures:
- GPUBlendComponent
- GPUColor
- GPUExtent3D
- GPULimits
- GPUOrigin3D
- GPUStencilFaceState
- GPUVertexAttribute
- GPUBlendState

In the next patch we will support memcpy on the qualified structures
whose members contain pointers (e.g. GPUVertexBufferLayout).

BUG=chromium:1266727

Change-Id: If46289f2d10cc7b17e6f5330cd2c2d4dc481f8b9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/73000
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

generator/dawn_json_generator.py

@@ -242,6 +242,21 @@ class StructureType(Record, Type):
         # two nextInChain members.
         assert not (self.extensible and self.chained)
 
+    def update_metadata(self):
+        Record.update_metadata(self)
+
+        if self.may_have_dawn_object:
+            self.is_wire_transparent = False
+            return
+
+        assert not (self.chained or self.extensible)
+
+        def get_is_wire_transparent(member):
+            return member.type.is_wire_transparent and member.annotation == 'value'
+
+        self.is_wire_transparent = all(
+            get_is_wire_transparent(m) for m in self.members)
+
     @property
     def output(self):
         return self.chained == "out" or self.extensible == "out"

generator/templates/dawn_wire/WireCmd.cpp

@@ -63,9 +63,14 @@
     {%- if member.type.category == "object" -%}
         {%- set Optional = "Optional" if member.optional else "" -%}
         WIRE_TRY(provider.Get{{Optional}}Id({{in}}, &{{out}}));
-    {% elif member.type.category == "structure"%}
+    {%- elif member.type.category == "structure" -%}
+        {%- if member.type.is_wire_transparent -%}
+            static_assert(sizeof({{out}}) == sizeof({{in}}), "Serialize memcpy size must match.");
+            memcpy(&{{out}}, &{{in}}, {{member_transfer_sizeof(member)}});
+        {%- else -%}
             {%- set Provider = ", provider" if member.type.may_have_dawn_object else "" -%}
             WIRE_TRY({{as_cType(member.type.name)}}Serialize({{in}}, &{{out}}, buffer{{Provider}}));
+        {%- endif -%}
     {%- else -%}
         {{out}} = {{in}};
     {%- endif -%}
@@ -77,11 +82,16 @@
         {%- set Optional = "Optional" if member.optional else "" -%}
         WIRE_TRY(resolver.Get{{Optional}}FromId({{in}}, &{{out}}));
     {%- elif member.type.category == "structure" -%}
+        {%- if member.type.is_wire_transparent -%}
+            static_assert(sizeof({{out}}) == sizeof({{in}}), "Deserialize memcpy size must match.");
+            memcpy(&{{out}}, const_cast<const {{member_transfer_type(member)}}*>(&{{in}}), {{member_transfer_sizeof(member)}});
+        {%- else -%}
             WIRE_TRY({{as_cType(member.type.name)}}Deserialize(&{{out}}, &{{in}}, deserializeBuffer, allocator
                 {%- if member.type.may_have_dawn_object -%}
                     , resolver
                 {%- endif -%}
             ));
+        {%- endif -%}
     {%- else -%}
         static_assert(sizeof({{out}}) >= sizeof({{in}}), "Deserialize assignment may not narrow.");
         {{out}} = {{in}};