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    DFG tier-up should happen in prologues, not epilogues · 16e2cbf7
    fpizlo@apple.com authored
    https://bugs.webkit.org/show_bug.cgi?id=89752
    
    Reviewed by Geoffrey Garen.
    
    This change has two outcomes:
            
    1) Slightly reduces the likelihood that a function will be optimized both
    standalone and via inlining.  Previously, if you had a call sequence like foo() 
    calls bar() exactly once, and nobody else calls bar(), then bar() would get
    optimized first (because it returns first) and then foo() gets optimized.  If foo()
    can inline bar() then that means that bar() gets optimized twice.  But now, if we
    optimize in prologues, then foo() will be optimized first.  If it inlines bar(),
    that means that there will no longer be any calls to bar().
            
    2) It lets us kill some code in JITStubs.  Epilogue tier-up was very different from
    loop tier-up, since epilogue tier-up should not attempt OSR.  But prologue tier-up
    requires OSR (albeit really easy OSR since it's the top of the compilation unit),
    so it becomes just like loop tier-up.  As a result, we now have one optimization
    hook (cti_optimize) instead of two (cti_optimize_from_loop and
    cti_optimize_from_ret).
            
    As a consequence of not having an optimization check in epilogues, the OSR exit
    code must now trigger reoptimization itself instead of just signaling the epilogue
    check to fire.
            
    This also adds the ability to count the number of DFG compilations, which was
    useful for debugging this patch and might be useful for other things in the future.
    
    * bytecode/CodeBlock.cpp:
    (JSC::CodeBlock::reoptimize):
    (JSC):
    * bytecode/CodeBlock.h:
    (CodeBlock):
    * dfg/DFGByteCodeParser.cpp:
    (JSC::DFG::ByteCodeParser::parseCodeBlock):
    * dfg/DFGDriver.cpp:
    (DFG):
    (JSC::DFG::getNumCompilations):
    (JSC::DFG::compile):
    * dfg/DFGDriver.h:
    (DFG):
    * dfg/DFGOSRExitCompiler.cpp:
    (JSC::DFG::OSRExitCompiler::handleExitCounts):
    * dfg/DFGOperations.cpp:
    * dfg/DFGOperations.h:
    * jit/JIT.cpp:
    (JSC::JIT::emitOptimizationCheck):
    * jit/JIT.h:
    * jit/JITCall32_64.cpp:
    (JSC::JIT::emit_op_ret):
    (JSC::JIT::emit_op_ret_object_or_this):
    * jit/JITOpcodes.cpp:
    (JSC::JIT::emit_op_ret):
    (JSC::JIT::emit_op_ret_object_or_this):
    (JSC::JIT::emit_op_enter):
    * jit/JITOpcodes32_64.cpp:
    (JSC::JIT::emit_op_enter):
    * jit/JITStubs.cpp:
    (JSC::DEFINE_STUB_FUNCTION):
    * jit/JITStubs.h:
    
    
    
    git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121073 268f45cc-cd09-0410-ab3c-d52691b4dbfc
    16e2cbf7