tree 022b736ad89328ac5442d62dd344bfe22db13273
parent ff9c6e48f3add2399713e28a9d952b7902b9cd58
author mark.lam@apple.com <mark.lam@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1571291158 +0000
committer mark.lam@apple.com <mark.lam@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1571291158 +0000

Reduce the amount of memory needed to store Options.
https://bugs.webkit.org/show_bug.cgi?id=202105

Reviewed by Yusuke Suzuki.

The size of the JSC::Config needed to store the Options is now reduced to 4K
instead of 16K, enabled by constexpr template magic.

1. Instead of all options in a large array of OptionEntry (which is a union of
   all the option types), we now have separate arrays for each of the types of
   options.  For example,

        Removed g_jscConfig.options[].
        Added g_jscConfig.typeBoolOptions[].
        Added g_jscConfig.typeInt32Options[].
        Added g_jscConfig.typeDoubleOptions[].
        ...

   We used to find the storage for the option using g_jscConfig.options[Options::ID].
   We now find the storage for each type of option using
   g_jscConfig.options[optionTypeSpecificIndex<OptionTypeID, OptionID>()].  For
   example, Options::useJIT() used to be implemented as:

       inline bool& Options::useJIT()
       {
            return g_jscConfig.options[Options::useJITID];
       }

   ... which is now replaced with:

       inline bool& Options::useJIT()
       {
            return g_jscConfig.typeBoolOptions[optionTypeSpecificIndex<OptionTypeID::Bool, OptionID::useJIT>()];
       }

   MSVC has a bug where it cannot handle very large source files: see
   https://developercommunity.visualstudio.com/content/problem/653301/fatal-error-c1002-compiler-is-out-of-heap-space-in.html.
   This bug prevents this patch from building on MSVC.  To workaround this bug,
   we don't inline the Options accessors when COMPILER(MSVC).  This prevents MSVC
   from having to parse the large body of template code code to used to implement
   the inline accessors in every file that #include "Options.h".

   Also add the @no-unify attribute to Options.cpp (where we put the accessors)
   so that it doesn't trigger the MSVC bug also.

2. Introduce the optionTypeSpecificIndex() constexpr template function for
   computing the index of each option in their respective type specific options
   array.

3. Introduce OptionTypes, OptionTypeID, and OptionID.

   The OptionTypes namespace replaces OptionEntry as the container of option types.
   The OptionID enum class replaces Options::ID.
   The OptionTypeID enum class is new and is used together with OptionID in
       constexpr templates to compute the typeSpecificIndex of options.

4. Removed the OptionEntry struct and OptionEntry.h.  After (1), this struct is
   only used in the Option class.  We just moved the union of option types (that
   OptionEntry embeds) into the Option class.

   Moved class OptionRange into OptionsList.h.

5. Removed the large OptionEntry arrays from JSC::Config.
   Added type specific options arrays.
   Also ordered these arrays to maximize compactness and minimize internal fragmentation.

6. Changed scaleJITPolicy() to go directly to g_jscConfig.typeInt32Options[]
   instead of going through the Option wrapper object.  This allows us to simplify
   things and make the Option class a read only interface of options.

7. Changed Options::initialize() to only compute the option default value once.
   The default value specified in the OptionsList may not always be a constant.
   Sometimes, it is a function call.

8. The Option class now only gives read only access to the options.

   The Option class' role is to provide an interface for reading an option at any
   given OptionID without first knowing about the type of the specific option.
   It is useful for iterating options, and is currently only used by
   Options::dumpOption().

   Technically, we could merge all the Option class code into its single client.
   We opted not to do this because the amount of code is non-trivial, and the
   Option class does a good job of encapsulating this functionality.

* API/glib/JSCOptions.cpp:
(jscOptionsSetValue):
(jscOptionsGetValue):
(jsc_options_foreach):
(jsc_options_get_option_group):
* CMakeLists.txt:
* JavaScriptCore.xcodeproj/project.pbxproj:
* Sources.txt:
* runtime/JSCConfig.h:
* runtime/OptionEntry.h: Removed.
* runtime/Options.cpp:
(JSC::Options::isAvailable):
(JSC::overrideOptionWithHeuristic):
(JSC::optionTypeSpecificIndex):
(JSC::scaleJITPolicy):
(JSC::recomputeDependentOptions):
(JSC::Options::initialize):
(JSC::Options::setOptionWithoutAlias):
(JSC::Options::dumpAllOptions):
(JSC::Options::dumpOption):
(JSC::Option::Option):
(JSC::Option::defaultOption const):
(JSC::Option::dump const):
(JSC::Option::operator== const):
* runtime/Options.h:
(JSC::Option::id const):
(JSC::Option::name const):
(JSC::Option::description const):
(JSC::Option::type const):
(JSC::Option::availability const):
(JSC::Option::isOverridden const):
(JSC::Option::Option):
(JSC::Option::idIndex const):
(JSC::optionTypeSpecificIndex):
(JSC::Option::defaultOption const): Deleted.
(JSC::Option::boolVal): Deleted.
(JSC::Option::unsignedVal): Deleted.
(JSC::Option::doubleVal): Deleted.
(JSC::Option::int32Val): Deleted.
(JSC::Option::optionRangeVal): Deleted.
(JSC::Option::optionStringVal): Deleted.
(JSC::Option::gcLogLevelVal): Deleted.
* runtime/OptionsList.h:
(JSC::OptionRange::operator= ):
(JSC::OptionRange::rangeString const):
(JSC::countNumberOfJSCOptionsOfType):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@251226 268f45cc-cd09-0410-ab3c-d52691b4dbfc