Changeset 35309 in webkit for trunk/JavaScriptCore/VM/CodeBlock.h

Timestamp:

Jul 23, 2008, 5:49:46 PM (17 years ago)

Author:

[email protected]

Message:

Improve switch performance.

Reviewed by Geoff Garen and Sam Weinig.

Improve switch performance by converting to a hashmap based jump
table to avoid the sequence of dispatches that would otherwise be
needed. This results in a 9-19x performance win for string switches
based on ad hoc testing, and a 6x improvement for integer switch
statements. SunSpider reports a 1.2% progression.

File:

• trunk/JavaScriptCore/VM/CodeBlock.h (modified) (2 diffs)

trunk/JavaScriptCore/VM/CodeBlock.h

@@ -67 +67 @@
     };
 
+    typedef HashMap<RefPtr<UString::Rep>, int32_t> StringJumpTable;
+    struct SimpleJumpTable {
+        Vector<int32_t> branchOffsets;
+        int32_t min;
+        int32_t offsetForValue(int32_t value, int32_t defaultOffset);
+        void add(int32_t key, int32_t offset) {
+            if (!branchOffsets[key])
+                branchOffsets[key] = offset;
+        }
+    };
+
     struct CodeBlock {
         CodeBlock(ScopeNode* ownerNode_, CodeType codeType_, PassRefPtr<SourceProvider> source_, unsigned sourceOffset_)
@@ -113 +124 @@
         Vector<LineInfo> lineInfo;
 
+        Vector<SimpleJumpTable> immediateSwitchJumpTables;
+        Vector<SimpleJumpTable> characterSwitchJumpTables;
+        Vector<StringJumpTable> stringSwitchJumpTables;
+
     private:
         void dump(ExecState*, const Vector<Instruction>::const_iterator& begin, Vector<Instruction>::const_iterator&) const;