Changeset 271121 in webkit for trunk/Source/JavaScriptCore/parser/Nodes.h

Timestamp:

Jan 2, 2021, 12:46:24 PM (4 years ago)

Author:

[email protected]

Message:

[JSC] Remove unnecessary mov bytecodes when performing simple object pattern destructuring to variables
​https://bugs.webkit.org/show_bug.cgi?id=220219

Reviewed by Alexey Shvayka.

JSTests:

• stress/object-pattern-simple-fast-path.js: Added.

(shouldBe):
(shouldThrow):
(test1):

Source/JavaScriptCore:

Currently, we are first puts object pattern's expression into temporary variable, and then, we store it into local variable register.

The following code

({ data } = object);

emits this kind of bytecode.

get_by_id dst:loc10, base:loc9, property:0
mov dst:loc6, src:loc10

However, this should be

get_by_id dst:loc6, base:loc9, property:0

We are emitting many unnecessary movs since this destructuring pattern is common. Increasing amount of mov (1) discourages inlining unnecessarily and (2) simply makes
bytecode memory large. Since this is very common pattern, we should carefully optimize it to remove such unnecessary movs.

This patch looks into pattern when performing object pattern destructuring. And avoid emitting mov when it is possible. There are some cases we cannot remove movs, so
this patch's writableDirectBindingIfPossible looks into whether this is possible (& profitable).

• bytecompiler/NodesCodegen.cpp:

(JSC::ObjectPatternNode::bindValue const):
(JSC::BindingNode::writableDirectBindingIfPossible const):
(JSC::BindingNode::finishDirectBindingAssignment const):
(JSC::AssignmentElementNode::writableDirectBindingIfPossible const):
(JSC::AssignmentElementNode::finishDirectBindingAssignment const):

• parser/Nodes.h:

(JSC::DestructuringPatternNode::writableDirectBindingIfPossible const):
(JSC::DestructuringPatternNode::finishDirectBindingAssignment const):

File:

• trunk/Source/JavaScriptCore/parser/Nodes.h (modified) (3 diffs)

trunk/Source/JavaScriptCore/parser/Nodes.h

@@ -2375 +2375 @@
         virtual bool isRestParameter() const { return false; }
         virtual RegisterID* emitDirectBinding(BytecodeGenerator&, RegisterID*, ExpressionNode*) { return nullptr; }
+
+        virtual RegisterID* writableDirectBindingIfPossible(BytecodeGenerator&) const { return nullptr; }
+        virtual void finishDirectBindingAssignment(BytecodeGenerator&) const { }
         
     protected:
@@ -2461 +2464 @@
         const JSTextPosition& divotStart() const { return m_divotStart; }
         const JSTextPosition& divotEnd() const { return m_divotEnd; }
+
+        RegisterID* writableDirectBindingIfPossible(BytecodeGenerator&) const final;
+        void finishDirectBindingAssignment(BytecodeGenerator&) const;
         
     private:
@@ -2499 +2505 @@
         const JSTextPosition& divotStart() const { return m_divotStart; }
         const JSTextPosition& divotEnd() const { return m_divotEnd; }
+
+        RegisterID* writableDirectBindingIfPossible(BytecodeGenerator&) const final;
+        void finishDirectBindingAssignment(BytecodeGenerator&) const;
 
     private: