script: Make PartialEq on element type IDs generate a lot less code.

This makes the difference between selector matching scaling on the ARM
Cortex-A9 and not, because the auto-derived `PartialEq` implementation
blows out the 32KB I-cache. With this change, there is a 2x improvement
in selector matching over sequential when using all 8 cores. (More work
needs to be done; this is a start.)

components/script/dom/eventtarget.rs

@@ -28,6 +28,7 @@ use std::collections::hash_map::Entry::{Occupied, Vacant};
 use std::collections::hash_state::DefaultState;
 use std::default::Default;
 use std::ffi::CString;
+use std::intrinsics;
 use std::ptr;
 use url::Url;
 
@@ -40,7 +41,7 @@ pub enum ListenerPhase {
     Bubbling,
 }
 
-#[derive(Copy, Clone, PartialEq)]
+#[derive(Copy, Clone)]
 #[jstraceable]
 pub enum EventTargetTypeId {
     Node(NodeTypeId),
@@ -51,6 +52,42 @@ pub enum EventTargetTypeId {
     XMLHttpRequestEventTarget(XMLHttpRequestEventTargetTypeId)
 }
 
+impl PartialEq for EventTargetTypeId {
+    #[inline]
+    fn eq(&self, other: &EventTargetTypeId) -> bool {
+        match (*self, *other) {
+            (EventTargetTypeId::Node(this_type), EventTargetTypeId::Node(other_type)) => {
+                this_type == other_type
+            }
+            _ => self.eq_slow(other)
+        }
+    }
+}
+
+impl EventTargetTypeId {
+    #[allow(unsafe_code)]
+    fn eq_slow(&self, other: &EventTargetTypeId) -> bool {
+        match (*self, *other) {
+            (EventTargetTypeId::Node(this_type), EventTargetTypeId::Node(other_type)) => {
+                this_type == other_type
+            }
+            (EventTargetTypeId::WorkerGlobalScope(this_type),
+             EventTargetTypeId::WorkerGlobalScope(other_type)) => {
+                this_type == other_type
+            }
+            (EventTargetTypeId::XMLHttpRequestEventTarget(this_type),
+             EventTargetTypeId::XMLHttpRequestEventTarget(other_type)) => {
+                this_type == other_type
+            }
+            (_, _) => {
+                unsafe {
+                    intrinsics::discriminant_value(self) == intrinsics::discriminant_value(other)
+                }
+            }
+        }
+    }
+}
+
 #[derive(Copy, Clone, PartialEq)]
 #[jstraceable]
 pub enum EventListenerType {

components/script/dom/htmlelement.rs

@@ -36,6 +36,7 @@ use string_cache::Atom;
 
 use std::borrow::ToOwned;
 use std::default::Default;
+use std::intrinsics;
 
 #[dom_struct]
 pub struct HTMLElement {
@@ -303,7 +304,7 @@ impl<'a> VirtualMethods for JSRef<'a, HTMLElement> {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Debug)]
+#[derive(Copy, Clone, Debug)]
 #[jstraceable]
 pub enum HTMLElementTypeId {
     HTMLElement,
@@ -374,3 +375,25 @@ pub enum HTMLElementTypeId {
     HTMLUnknownElement,
 }
 
+impl PartialEq for HTMLElementTypeId {
+    #[inline]
+    #[allow(unsafe_code)]
+    fn eq(&self, other: &HTMLElementTypeId) -> bool {
+        match (*self, *other) {
+            (HTMLElementTypeId::HTMLMediaElement(this_type),
+             HTMLElementTypeId::HTMLMediaElement(other_type)) => {
+                this_type == other_type
+            }
+            (HTMLElementTypeId::HTMLTableCellElement(this_type),
+             HTMLElementTypeId::HTMLTableCellElement(other_type)) => {
+                this_type == other_type
+            }
+            (_, _) => {
+                unsafe {
+                    intrinsics::discriminant_value(self) == intrinsics::discriminant_value(other)
+                }
+            }
+        }
+    }
+}
+

components/script/dom/htmlmediaelement.rs

@@ -42,10 +42,17 @@ impl HTMLMediaElement {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Debug)]
+#[derive(Copy, Clone, Debug)]
 #[jstraceable]
 pub enum HTMLMediaElementTypeId {
-    HTMLAudioElement,
-    HTMLVideoElement,
+    HTMLAudioElement = 0,
+    HTMLVideoElement = 1,
+}
+
+impl PartialEq for HTMLMediaElementTypeId {
+    #[inline]
+    fn eq(&self, other: &HTMLMediaElementTypeId) -> bool {
+        (*self as u8) == (*other as u8)
+    }
 }
 

components/script/dom/htmltablecellelement.rs

@@ -23,11 +23,18 @@ use std::cmp::max;
 
 const DEFAULT_COLSPAN: u32 = 1;
 
-#[derive(Copy, Clone, PartialEq, Debug)]
+#[derive(Copy, Clone, Debug)]
 #[jstraceable]
 pub enum HTMLTableCellElementTypeId {
-    HTMLTableDataCellElement,
-    HTMLTableHeaderCellElement,
+    HTMLTableDataCellElement = 0,
+    HTMLTableHeaderCellElement = 1,
+}
+
+impl PartialEq for HTMLTableCellElementTypeId {
+    #[inline]
+    fn eq(&self, other: &HTMLTableCellElementTypeId) -> bool {
+        (*self as u8) == (*other as u8)
+    }
 }
 
 #[dom_struct]
@@ -143,3 +150,4 @@ impl<'a> VirtualMethods for JSRef<'a, HTMLTableCellElement> {
         }
     }
 }
+