Changeset 128219 in webkit for trunk/Source/JavaScriptCore/bytecode/CodeBlock.cpp

Timestamp:

Sep 11, 2012, 1:00:31 PM (13 years ago)

Author:

[email protected]

Message:

LLInt should optimize and profile array length accesses
​https://bugs.webkit.org/show_bug.cgi?id=96417

Reviewed by Oliver Hunt.

This fixes the following hole in our array profiling strategy, where the array
is large (more than 1000 elements):

for (var i = 0; i < array.length; ++i) ...

The peeled use of array.length (in the array prologue) will execute only once
before DFG optimization kicks in from the loop's OSR point. Since it executed
only once, it executed in the LLInt. And prior to this patch, the LLInt did
not profile array.length accesses - so the DFG will assume, based on the lack
of profiling, that the access is in fact not an access to the JSArray length
property. That could then impede our ability to hoist the array structure
check, and may make us pessimistic in other ways as well, since the generic
GetById used for the array length access will be viewed as a side-effecting
operation.

• bytecode/CodeBlock.cpp:

(JSC::CodeBlock::printGetByIdCacheStatus):
(JSC::CodeBlock::finalizeUnconditionally):

• bytecode/GetByIdStatus.cpp:

(JSC::GetByIdStatus::computeFromLLInt):

• dfg/DFGByteCodeParser.cpp:

(JSC::DFG::ByteCodeParser::parseBlock):

• dfg/DFGCapabilities.h:

(JSC::DFG::canCompileOpcode):

• dfg/DFGFixupPhase.cpp:

(JSC::DFG::FixupPhase::fixupNode):

• jit/JIT.cpp:

(JSC::JIT::privateCompileMainPass):
(JSC::JIT::privateCompileSlowCases):

• llint/LLIntSlowPaths.cpp:

(JSC::LLInt::LLINT_SLOW_PATH_DECL):

• llint/LowLevelInterpreter.asm:
• llint/LowLevelInterpreter32_64.asm:
• llint/LowLevelInterpreter64.asm:

File:

• trunk/Source/JavaScriptCore/bytecode/CodeBlock.cpp (modified) (2 diffs)

trunk/Source/JavaScriptCore/bytecode/CodeBlock.cpp

@@ -292 +292 @@
     
 #if ENABLE(LLINT)
-    Structure* structure = instruction[4].u.structure.get();
-    dataLog(" llint(");
-    dumpStructure("struct", exec, structure, ident);
-    dataLog(")");
+    if (exec->interpreter()->getOpcodeID(instruction[0].u.opcode) == op_get_array_length)
+        dataLog(" llint(array_length)");
+    else {
+        Structure* structure = instruction[4].u.structure.get();
+        dataLog(" llint(");
+        dumpStructure("struct", exec, structure, ident);
+        dataLog(")");
+    }
 #endif
 
@@ -2082 +2086 @@
                 curInstruction[0].u.opcode = interpreter->getOpcode(op_put_by_id);
                 break;
+            case op_get_array_length:
+                break;
             default:
                 ASSERT_NOT_REACHED();