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mark.lam@apple.com authored
<https://webkit.org/b/122836> Reviewed by Geoffrey Garen. Previously we gained back some performance (run at baseline JIT speeds) when the WebInspector is opened provided no breakpoints are set. This was achieved by simply skipping all op_debug callbacks to the debugger if no breakpoints are set. If any breakpoints are set, the debugger will set a m_needsOpDebugCallbacks flag which causes the callbacks to be called, and we don't get the baseline JIT speeds anymore. With this patch, we will now track the number of breakpoints set in the CodeBlock that they are set in. The LLINT and baseline JIT code will check CodeBlock::m_numBreakpoints to determine if the op_debug callbacks need to be called. With this, we will only enable op_debug callbacks for CodeBlocks that need it i.e. those with breakpoints set in them. Debugger::m_needsOpDebugCallbacks is now obsoleted. The LLINT and baseline JIT code still needs to check Debugger::m_shouldPause to determine if the debugger is in stepping mode and hence, needs op_debug callbacks enabled for everything until the debugger "continues" the run and exit stepping mode. Also in this patch, I fixed a regression in DOM breakpoints which relies Debugger::breakProgram() to pause the debugger. * bytecode/CodeBlock.cpp: (JSC::CodeBlock::dumpBytecode): - Missed accounting for op_debug's new hasBreakpointFlag operand here when it was added. (JSC::CodeBlock::CodeBlock): (JSC::CodeBlock::hasOpDebugForLineAndColumn): - This is needed in Debugger::toggleBreakpoint() to determine if a breakpoint falls within a CodeBlock or not. Simply checking the bounds of the CodeBlock is insufficient. For example, let's say we have the following JS code: // begin global scope function f1() { function f2() { ... // set breakpoint here. } } // end global scope Using the CodeBlock bounds alone, the breakpoint above will to appear to be in the global program CodeBlock, and the CodeBlocks for function f1() and f2(). With CodeBlock::hasOpDebugForLineAndColumn() we can rule out the global program CodeBlock and f1(), and only apply the breakpoint to f2(0 where it belongs. CodeBlock::hasOpDebugForLineAndColumn() works by iterating over all the opcodes in the CodeBlock to look for op_debug's. For each op_debug, it calls CodeBlock::expressionRangeForBytecodeOffset() to do a binary seach to get the line and column info for that op_debug. This is a N * log(N) algorithm. However, a quick hands on test using the WebInspector (with this patch applied) to exercise setting, breaking on, and clearing breakpoints, as well as stepping through some code shows no noticeable degradation of the user experience compared to the baseline without this patch. * bytecode/CodeBlock.h: (JSC::CodeBlock::numBreakpoints): (JSC::CodeBlock::numBreakpointsOffset): (JSC::CodeBlock::addBreakpoint): (JSC::CodeBlock::removeBreakpoint): (JSC::CodeBlock::clearAllBreakpoints): * debugger/Breakpoint.h: - defined Breakpoint::unspecifiedColumn so that we can explicitly indicate when the WebInspector was setting a line breakpoint and did not provide a column value. CodeBlock::hasOpDebugForLineAndColumn() needs this information in order to loosen its matching criteria for op_debug bytecodes for the specified breakpoint line and column values provided by the debugger. Previously, we just hijack a 0 value column as an unspecified column. However, the WebInspector operates on 0-based ints for column values. Hence, 0 should be a valid column value and should not be hijacked to mean an unspecified column. * debugger/Debugger.cpp: (JSC::Debugger::Debugger): - added tracking of the VM that the debugger is used with. This is needed by Debugger::breakProgram(). The VM pointer is attained from the first JSGlobalObject that the debugger attaches to. When the debugger detaches from the last JSGlobalObject, it will nullify its VM pointer to allow a new one to be set on the next attach. We were always only using each debugger instance with one VM. This change makes it explicit with an assert to ensure that all globalObjects that the debugger attaches to beongs to the same VM. (JSC::Debugger::attach): (JSC::Debugger::detach): (JSC::Debugger::setShouldPause): (JSC::Debugger::registerCodeBlock): (JSC::Debugger::unregisterCodeBlock): - registerCodeBlock() is responsible for applying pre-existing breakpoints to new CodeBlocks being installed. Similarly, unregisterCodeBlock() clears the breakpoints. (JSC::Debugger::toggleBreakpoint): - This is the workhorse function that checks if a breakpoint falls within a CodeBlock or not. If it does, then it can either enable or disable said breakpoint in the CodeBlock. In the current implementation, enabling/disabling the breakpoint simply means incrementing/decrementing the CodeBlock's m_numBreakpoints. (JSC::Debugger::applyBreakpoints): (JSC::Debugger::ToggleBreakpointFunctor::ToggleBreakpointFunctor): (JSC::Debugger::ToggleBreakpointFunctor::operator()): (JSC::Debugger::toggleBreakpoint): - Iterates all relevant CodeBlocks and apply the specified breakpoint if appropriate. This is called when a new breakpoint is being defined by the WebInspector and needs to be applied to an already installed CodeBlock. (JSC::Debugger::setBreakpoint): (JSC::Debugger::removeBreakpoint): (JSC::Debugger::hasBreakpoint): (JSC::Debugger::ClearBreakpointsFunctor::ClearBreakpointsFunctor): (JSC::Debugger::ClearBreakpointsFunctor::operator()): (JSC::Debugger::clearBreakpoints): (JSC::Debugger::breakProgram): - Fixed a regression that broke DOM breakpoints. The issue is that with the skipping of op_debug callbacks, we don't always have an updated m_currentCallFrame. Normally, m_currentCallFrame is provided as arg in the op_debug callback. In this case, we can get the CallFrame* from m_vm->topCallFrame. (JSC::Debugger::updateCallFrameAndPauseIfNeeded): (JSC::Debugger::pauseIfNeeded): (JSC::Debugger::willExecuteProgram): * debugger/Debugger.h: (JSC::Debugger::Debugger): (JSC::Debugger::shouldPause): * heap/CodeBlockSet.h: (JSC::CodeBlockSet::iterate): * heap/Heap.h: (JSC::Heap::forEachCodeBlock): - Added utility to iterate all CodeBlocks in the heap / VM. * interpreter/Interpreter.cpp: (JSC::Interpreter::debug): * jit/JITOpcodes.cpp: (JSC::JIT::emit_op_debug): * jit/JITOpcodes32_64.cpp: (JSC::JIT::emit_op_debug): * llint/LowLevelInterpreter.asm: - These now checks CodeBlock::m_numBreakpoints and Debugger::m_shouldPause instead of Debugger::m_needsOpDebugCallbacks. * runtime/Executable.cpp: (JSC::ScriptExecutable::installCode): git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162598 268f45cc-cd09-0410-ab3c-d52691b4dbfc
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