REGRESSION(r180595): same-callee profiling no longer works
https://bugs.webkit.org/show_bug.cgi?id=144787
Reviewed by Filip Pizlo.
This patch introduces a DFG optimization to use NewObject node when the callee of op_create_this is
always the same JSFunction. This condition doesn't hold when the byte code creates multiple
JSFunction objects at runtime as in: function y() { return function () {} }; new y(); new y();
To enable this optimization, LLint and baseline JIT now store the last callee we saw in the newly
added fourth operand of op_create_this. We use this JSFunction's structure in DFG after verifying
our speculation that the callee is the same. To avoid recompiling the same code for different callee
objects in the polymorphic case, the special value of seenMultipleCalleeObjects() is set in
LLint and baseline JIT when multiple callees are observed.
Tests: stress/create-this-with-callee-variants.js
- bytecode/BytecodeList.json: Increased the number of operands to 5.
- bytecode/CodeBlock.cpp:
(JSC::CodeBlock::dumpBytecode): Dump the newly added callee cache.
(JSC::CodeBlock::finalizeUnconditionally): Clear the callee cache if the callee is no longer alive.
- bytecompiler/BytecodeGenerator.cpp:
(JSC::BytecodeGenerator::emitCreateThis): Add the instruction to propertyAccessInstructions so that
we can clear the callee cache in CodeBlock::finalizeUnconditionally. Also initialize the newly added
operand.
- dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::parseBlock): Implement the optimization. Speculate the actual callee to
match the cache. Use the cached callee's structure if the speculation succeeds. Otherwise, OSR exit.
(JSC::JIT::emit_op_create_this): Go to the slow path to update the cache unless it's already marked
as seenMultipleCalleeObjects() to indicate the polymorphic behavior and/or we've OSR exited here.
(JSC::JIT::emitSlow_op_create_this):
(JSC::JIT::emit_op_create_this): Ditto.
(JSC::JIT::emitSlow_op_create_this):
- llint/LowLevelInterpreter32_64.asm:
(_llint_op_create_this): Ditto.
- llint/LowLevelInterpreter64.asm:
(_llint_op_create_this): Ditto.
- runtime/CommonSlowPaths.cpp:
(slow_path_create_this): Set the callee cache to the actual callee if it's not set. If the cache has
been set to a JSFunction* different from the actual callee, set it to seenMultipleCalleeObjects().
(JSC::JSCell::seenMultipleCalleeObjects): Added.
(JSC::WriteBarrierBase::unvalidatedGet): Removed the compile guard around it.
- tests/stress/create-this-with-callee-variants.js: Added.
