Restructure global variable constant inference so that it could work for any kind of symbol table variable
https://bugs.webkit.org/show_bug.cgi?id=124760

Reviewed by Oliver Hunt.
        
This changes the way global variable constant inference works so that it can be reused
for closure variable constant inference. Some of the premises that originally motivated
this patch are somewhat wrong, but it led to some simplifications anyway and I suspect
that we'll be able to fix those premises in the future. The main point of this patch is
to make it easy to reuse global variable constant inference for closure variable
constant inference, and this will be possible provided we can also either (a) infer
one-shot closures (easy) or (b) infer closure variables that are always assigned prior
to first use.
        
One of the things that this patch is meant to enable is constant inference for closure
variables that may be part of a multi-shot closure. Closure variables may be
instantiated multiple times, like:
        
    function foo() {
        var WIDTH = 45;
        function bar() {
            ... use WIDTH ...
        }
        ...
    }
        
Even if foo() is called many times and WIDTH is assigned to multiple times, that
doesn't change the fact that it's a constant. The goal of closure variable constant
inference is to catch any case where a closure variable has been assigned at least once
and its value has never changed. This patch doesn't implement that, but it does change
global variable constant inference to have most of the powers needed to do that. Note
that most likely we will use this functionality only to implement constant inference
for one-shot closures, but the resulting machinery is still simpler than what we had
before.
        
This involves three changes:
        
    - The watchpoint object now contains the inferred value. This involves creating a
      new kind of watchpoint set, the VariableWatchpointSet. We will reuse this object
      for closure variables.
        
    - Writing to a variable that is watchpointed still involves these three states that
      we proceed through monotonically (Uninitialized->Initialized->Invalidated) but
      now, the Initialized->Invalidated state transition only happens if we change the
      variable's value, rather than store to the variable. Repeatedly storing the same
      value won't change the variable's state.
        
    - On 64-bit systems (the only systems on which we do concurrent JIT), you no longer
      need fancy fencing to get a consistent view of the watchpoint in the JIT. The
      state of the VariableWatchpointSet for the purposes of constant folding is
      entirely encapsulated in the VariableWatchpointSet::m_inferredValue. If that is
      JSValue() then you cannot fold (either because the set is uninitialized or
      because it's invalidated - doesn't matter which); on the other hand if the value
      is anything other than JSValue() then you can fold, and that's the value you fold
      to. Simple!
        
This also changes the way that DFG IR deals with variable watchpoints. It's now
oblivious to global variables. You install a watchpoint using VariableWatchpoint and
you notify write using NotifyWrite. Easy!
        
Note that this will requires some more tweaks because of the fact that op_enter will
store Undefined into every captured variable. Hence it won't even work for one-shot
closures. One-shot closures are easily fixed by introducing another state (so we'll
have Uninitialized->Undefined->Initialized->Invalidated). Multi-shot closures will
require static analysis. One-shot closures are clearly a higher priority.

* GNUmakefile.list.am:
* JavaScriptCore.vcxproj/JavaScriptCore.vcxproj:
* JavaScriptCore.xcodeproj/project.pbxproj:
* bytecode/Instruction.h:
* bytecode/VariableWatchpointSet.h: Added.
(JSC::VariableWatchpointSet::VariableWatchpointSet):
(JSC::VariableWatchpointSet::~VariableWatchpointSet):
(JSC::VariableWatchpointSet::inferredValue):
(JSC::VariableWatchpointSet::notifyWrite):
(JSC::VariableWatchpointSet::invalidate):
(JSC::VariableWatchpointSet::finalizeUnconditionally):
(JSC::VariableWatchpointSet::addressOfInferredValue):
* bytecode/Watchpoint.h:
* dfg/DFGAbstractInterpreterInlines.h:
(JSC::DFG::::executeEffects):
* dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::parseBlock):
* dfg/DFGCSEPhase.cpp:
(JSC::DFG::CSEPhase::performNodeCSE):
* dfg/DFGClobberize.h:
(JSC::DFG::clobberize):
* dfg/DFGFixupPhase.cpp:
(JSC::DFG::FixupPhase::fixupNode):
* dfg/DFGNode.h:
(JSC::DFG::Node::hasRegisterPointer):
(JSC::DFG::Node::hasVariableWatchpointSet):
(JSC::DFG::Node::variableWatchpointSet):
* dfg/DFGNodeType.h:
* dfg/DFGOperations.cpp:
* dfg/DFGOperations.h:
* dfg/DFGPredictionPropagationPhase.cpp:
(JSC::DFG::PredictionPropagationPhase::propagate):
* dfg/DFGSafeToExecute.h:
(JSC::DFG::safeToExecute):
* dfg/DFGSpeculativeJIT.cpp:
(JSC::DFG::SpeculativeJIT::compileArithMod):
* dfg/DFGSpeculativeJIT.h:
(JSC::DFG::SpeculativeJIT::callOperation):
* dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* dfg/DFGWatchpointCollectionPhase.cpp:
(JSC::DFG::WatchpointCollectionPhase::handle):
* ftl/FTLCapabilities.cpp:
(JSC::FTL::canCompile):
* ftl/FTLLowerDFGToLLVM.cpp:
(JSC::FTL::LowerDFGToLLVM::compileNode):
(JSC::FTL::LowerDFGToLLVM::compileNotifyWrite):
* jit/JIT.h:
* jit/JITOperations.h:
* jit/JITPropertyAccess.cpp:
(JSC::JIT::emitNotifyWrite):
(JSC::JIT::emitPutGlobalVar):
* jit/JITPropertyAccess32_64.cpp:
(JSC::JIT::emitNotifyWrite):
(JSC::JIT::emitPutGlobalVar):
* llint/LowLevelInterpreter32_64.asm:
* llint/LowLevelInterpreter64.asm:
* runtime/JSGlobalObject.cpp:
(JSC::JSGlobalObject::addGlobalVar):
(JSC::JSGlobalObject::addFunction):
* runtime/JSGlobalObject.h:
* runtime/JSScope.h:
(JSC::ResolveOp::ResolveOp):
* runtime/JSSymbolTableObject.h:
(JSC::symbolTablePut):
(JSC::symbolTablePutWithAttributes):
* runtime/SymbolTable.cpp:
(JSC::SymbolTableEntry::inferredValue):
(JSC::SymbolTableEntry::prepareToWatch):
(JSC::SymbolTableEntry::addWatchpoint):
(JSC::SymbolTableEntry::notifyWriteSlow):
(JSC::SymbolTable::visitChildren):
(JSC::SymbolTable::WatchpointCleanup::WatchpointCleanup):
(JSC::SymbolTable::WatchpointCleanup::~WatchpointCleanup):
(JSC::SymbolTable::WatchpointCleanup::finalizeUnconditionally):
* runtime/SymbolTable.h:
(JSC::SymbolTableEntry::watchpointSet):
(JSC::SymbolTableEntry::notifyWrite):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@159798 268f45cc-cd09-0410-ab3c-d52691b4dbfc