Changeset 128096 in webkit for trunk/Source/JavaScriptCore/bytecompiler

Timestamp:

Sep 10, 2012, 1:23:50 PM (13 years ago)

Author:

[email protected]

Message:

Refactored op_tear_off* to support activations that don't allocate space for 'arguments'
​https://bugs.webkit.org/show_bug.cgi?id=96231

Reviewed by Gavin Barraclough.

This is a step toward smaller activations.

As a side-effect, this patch eliminates a load and branch from the hot path
of activation tear-off by moving it to the cold path of arguments tear-off. Our
optimizing assumptions are that activations are common and that reifying the
arguments object is less common.

• bytecode/CodeBlock.cpp:

(JSC::CodeBlock::dump):

• bytecode/Opcode.h:

(JSC::padOpcodeName): Updated for new opcode lengths.

• bytecompiler/BytecodeGenerator.cpp:

(JSC::BytecodeGenerator::BytecodeGenerator):
(JSC::BytecodeGenerator::addConstantValue): Added support for JSValue()
in the bytecode, which we use when we have 'arguments' but no activation.

(JSC::BytecodeGenerator::emitReturn): Always emit tear_off_arguments
if we've allocated the arguments registers. This allows tear_off_activation
not to worry about the arguments object anymore.

Also, pass the activation and arguments values directly to these opcodes
instead of requiring the opcodes to infer the values through special
registers. This gives us more flexibility to move or eliminate registers.

• dfg/DFGArgumentsSimplificationPhase.cpp:

(JSC::DFG::ArgumentsSimplificationPhase::run):

• dfg/DFGByteCodeParser.cpp:

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

• dfg/DFGNode.h:

(Node): Updated for new opcode lengths.

• dfg/DFGOperations.cpp: Activation tear-off doesn't worry about the

arguments object anymore. If 'arguments' is in use and reified, it's
responsible for aliasing back to the activation object in tear_off_arguments.

• dfg/DFGOperations.h:
• dfg/DFGSpeculativeJIT.h:

(JSC::DFG::SpeculativeJIT::callOperation):
(SpeculativeJIT):

• dfg/DFGSpeculativeJIT32_64.cpp:

(JSC::DFG::SpeculativeJIT::compile):

• dfg/DFGSpeculativeJIT64.cpp:

(JSC::DFG::SpeculativeJIT::compile): Don't pass the arguments object to
activation tear-off; do pass the activation object to arguments tear-off.

• interpreter/Interpreter.cpp:

(JSC::Interpreter::privateExecute): Ditto.

• jit/JITOpcodes.cpp:

(JSC::JIT::emit_op_tear_off_activation):
(JSC::JIT::emit_op_tear_off_arguments):

• jit/JITOpcodes32_64.cpp:

(JSC::JIT::emit_op_tear_off_activation):
(JSC::JIT::emit_op_tear_off_arguments):

• jit/JITStubs.cpp:

(JSC::DEFINE_STUB_FUNCTION):

• llint/LLIntSlowPaths.cpp:

(JSC::LLInt::LLINT_SLOW_PATH_DECL):

• llint/LowLevelInterpreter32_64.asm:
• llint/LowLevelInterpreter64.asm: Same change in a few more execution engines.

Location:

trunk/Source/JavaScriptCore/bytecompiler

Files:

• BytecodeGenerator.cpp (modified) (6 diffs)
• BytecodeGenerator.h (modified) (2 diffs)

trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp

@@ -273 +273 @@
     , m_codeBlock(codeBlock)
     , m_thisRegister(CallFrame::thisArgumentOffset())
+    , m_emptyValueRegister(0)
     , m_finallyDepth(0)
     , m_dynamicScopeDepth(0)
@@ -354 +355 @@
     , m_codeBlock(codeBlock)
     , m_activationRegister(0)
+    , m_emptyValueRegister(0)
     , m_finallyDepth(0)
     , m_dynamicScopeDepth(0)
@@ -387 +389 @@
     }
 
-    // Both op_tear_off_activation and op_tear_off_arguments tear off the 'arguments'
-    // object, if created.
     if (m_codeBlock->needsFullScopeChain() || functionBody->usesArguments()) {
         RegisterID* unmodifiedArgumentsRegister = addVar(); // Anonymous, so it can't be modified by user code.
@@ -527 +527 @@
     , m_codeBlock(codeBlock)
     , m_thisRegister(CallFrame::thisArgumentOffset())
+    , m_emptyValueRegister(0)
     , m_finallyDepth(0)
     , m_dynamicScopeDepth(0)
@@ -1112 +1113 @@
 }
 
+// We can't hash JSValue(), so we use a dedicated data member to cache it.
+RegisterID* BytecodeGenerator::addConstantEmptyValue()
+{
+    if (!m_emptyValueRegister) {
+        int index = m_nextConstantOffset;
+        m_constantPoolRegisters.append(FirstConstantRegisterIndex + m_nextConstantOffset);
+        ++m_nextConstantOffset;
+        m_codeBlock->addConstant(JSValue());
+        m_emptyValueRegister = &m_constantPoolRegisters[index];
+    }
+
+    return m_emptyValueRegister;
+}
+
 RegisterID* BytecodeGenerator::addConstantValue(JSValue v)
 {
+    if (!v)
+        return addConstantEmptyValue();
+
     int index = m_nextConstantOffset;
-
     JSValueMap::AddResult result = m_jsValueMap.add(JSValue::encode(v), m_nextConstantOffset);
     if (result.isNewEntry) {
         m_constantPoolRegisters.append(FirstConstantRegisterIndex + m_nextConstantOffset);
         ++m_nextConstantOffset;
-        m_codeBlock->addConstant(JSValue(v));
+        m_codeBlock->addConstant(v);
     } else
         index = result.iterator->second;
-
     return &m_constantPoolRegisters[index];
 }
@@ -2047 +2063 @@
         emitOpcode(op_tear_off_activation);
         instructions().append(m_activationRegister->index());
-        instructions().append(m_codeBlock->argumentsRegister());
-    } else if (m_codeBlock->usesArguments() && m_codeBlock->numParameters() != 1 && !m_codeBlock->isStrictMode()) {
+    }
+
+    if (m_codeBlock->usesArguments() && m_codeBlock->numParameters() != 1 && !m_codeBlock->isStrictMode()) {
         emitOpcode(op_tear_off_arguments);
         instructions().append(m_codeBlock->argumentsRegister());
+        instructions().append(m_activationRegister ? m_activationRegister->index() : emitLoad(0, JSValue())->index());
     }
 

trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.h

@@ -638 +638 @@
         unsigned addConstant(const Identifier&);
         RegisterID* addConstantValue(JSValue);
+        RegisterID* addConstantEmptyValue();
         unsigned addRegExp(RegExp*);
 
@@ -714 +715 @@
         RegisterID m_calleeRegister;
         RegisterID* m_activationRegister;
+        RegisterID* m_emptyValueRegister;
         SegmentedVector<RegisterID, 32> m_constantPoolRegisters;
         SegmentedVector<RegisterID, 32> m_calleeRegisters;