gecko/js/src/jspropertycache.h

/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
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 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
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 * http://www.mozilla.org/MPL/
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 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla Communicator client code, released
 * March 31, 1998.
 *
 * The Initial Developer of the Original Code is
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 * Portions created by the Initial Developer are Copyright (C) 1998
 * the Initial Developer. All Rights Reserved.
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 *
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 * ***** END LICENSE BLOCK ***** */

#ifndef jspropertycache_h___
#define jspropertycache_h___

#include "jsapi.h"
#include "jsprvtd.h"
#include "jstypes.h"

namespace js {

/*
 * Property cache with structurally typed capabilities for invalidation, for
 * polymorphic callsite method/get/set speedups.  For details, see
 * <https://developer.mozilla.org/en/SpiderMonkey/Internals/Property_cache>.
 */

/* Property cache value capabilities. */
enum {
    PCVCAP_PROTOBITS = 4,
    PCVCAP_PROTOSIZE = JS_BIT(PCVCAP_PROTOBITS),
    PCVCAP_PROTOMASK = JS_BITMASK(PCVCAP_PROTOBITS),

    PCVCAP_SCOPEBITS = 4,
    PCVCAP_SCOPESIZE = JS_BIT(PCVCAP_SCOPEBITS),
    PCVCAP_SCOPEMASK = JS_BITMASK(PCVCAP_SCOPEBITS),

    PCVCAP_TAGBITS = PCVCAP_PROTOBITS + PCVCAP_SCOPEBITS,
    PCVCAP_TAGMASK = JS_BITMASK(PCVCAP_TAGBITS)
};

const uint32 SHAPE_OVERFLOW_BIT = JS_BIT(32 - PCVCAP_TAGBITS);

/*
 * Property cache value. This is simply a tagged union:
 *    PCVal = (JSObject * | uint32 | JSScopeProperty *).
 * It is the type of PropertyCacheEntry::vword and combines with the tag bits
 * of PropertyCacheEntry::vcap to tell how to get or set the property, once a
 * property cache hit is validated.
 *
 * PropertyCache::purge depends on the bit-pattern of a null PCVal being 0.
 */
class PCVal
{
  private:
    enum {
        OBJECT = 0,
        SLOT = 1,
        SPROP = 2,
        TAG = 3
    };

    jsuword v;

  public:
    bool isNull() const { return v == 0; }
    void setNull() { v = 0; }

    bool isObject() const { return (v & TAG) == OBJECT; }
    JSObject *toObject() const { JS_ASSERT(isObject()); return reinterpret_cast<JSObject *>(v); }
    jsval toJsval() const { return OBJECT_TO_JSVAL(toObject()); }
    void setObject(JSObject *obj) { v = reinterpret_cast<jsuword>(obj); }

    bool isSlot() const { return v & SLOT; }
    uint32 toSlot() const { JS_ASSERT(isSlot()); return uint32(v) >> 1; }
    void setSlot(uint32 slot) { v = (jsuword(slot) << 1) | SLOT; }

    bool isSprop() const { return (v & TAG) == SPROP; }
    JSScopeProperty *toSprop() const { JS_ASSERT(isSprop()); return reinterpret_cast<JSScopeProperty *>(v & ~TAG); }
    void setSprop(JSScopeProperty *sprop) { JS_ASSERT(sprop); v = reinterpret_cast<jsuword>(sprop) | SPROP; }
};

struct PropertyCacheEntry
{
    jsbytecode          *kpc;           /* pc of cache-testing bytecode */
    jsuword             kshape;         /* shape of direct (key) object */
    jsuword             vcap;           /* value capability, see above */
    PCVal               vword;          /* value word, see PCVal above */

    bool adding() const { return vcapTag() == 0 && kshape != vshape(); }
    bool directHit() const { return vcapTag() == 0 && kshape == vshape(); }

    jsuword vcapTag() const { return vcap & PCVCAP_TAGMASK; }
    uint32 vshape() const { return uint32(vcap >> PCVCAP_TAGBITS); }
    jsuword scopeIndex() const { return (vcap >> PCVCAP_PROTOBITS) & PCVCAP_SCOPEMASK; }
    jsuword protoIndex() const { return vcap & PCVCAP_PROTOMASK; }

    void assign(jsbytecode *kpc, jsuword kshape, jsuword vshape,
                uintN scopeIndex, uintN protoIndex, PCVal vword) {
        JS_ASSERT(kshape < SHAPE_OVERFLOW_BIT);
        JS_ASSERT(vshape < SHAPE_OVERFLOW_BIT);
        JS_ASSERT(scopeIndex <= PCVCAP_SCOPEMASK);
        JS_ASSERT(protoIndex <= PCVCAP_PROTOMASK);

        this->kpc = kpc;
        this->kshape = kshape;
        this->vcap = (vshape << PCVCAP_TAGBITS) | (scopeIndex << PCVCAP_PROTOBITS) | protoIndex;
        this->vword = vword;
    }
};

/*
 * Special value for functions returning PropertyCacheEntry * to distinguish
 * between failure and no no-cache-fill cases.
 */
#define JS_NO_PROP_CACHE_FILL ((js::PropertyCacheEntry *) NULL + 1)

#if defined DEBUG_brendan || defined DEBUG_brendaneich
#define JS_PROPERTY_CACHE_METERING 1
#endif

class PropertyCache
{
  private:
    enum {
        SIZE_LOG2 = 12,
        SIZE = JS_BIT(SIZE_LOG2),
        MASK = JS_BITMASK(SIZE_LOG2)
    };

    PropertyCacheEntry  table[SIZE];
    JSBool              empty;
#ifdef JS_PROPERTY_CACHE_METERING
  public:
    PropertyCacheEntry  *pctestentry;   /* entry of the last PC-based test */
    uint32              fills;          /* number of cache entry fills */
    uint32              nofills;        /* couldn't fill (e.g. default get) */
    uint32              rofills;        /* set on read-only prop can't fill */
    uint32              disfills;       /* fill attempts on disabled cache */
    uint32              oddfills;       /* fill attempt after setter deleted */
    uint32              modfills;       /* fill that rehashed to a new entry */
    uint32              brandfills;     /* scope brandings to type structural
                                           method fills */
    uint32              noprotos;       /* resolve-returned non-proto pobj */
    uint32              longchains;     /* overlong scope and/or proto chain */
    uint32              recycles;       /* cache entries recycled by fills */
    uint32              tests;          /* cache probes */
    uint32              pchits;         /* fast-path polymorphic op hits */
    uint32              protopchits;    /* pchits hitting immediate prototype */
    uint32              initests;       /* cache probes from JSOP_INITPROP */
    uint32              inipchits;      /* init'ing next property pchit case */
    uint32              inipcmisses;    /* init'ing next property pc misses */
    uint32              settests;       /* cache probes from JOF_SET opcodes */
    uint32              addpchits;      /* adding next property pchit case */
    uint32              setpchits;      /* setting existing property pchit */
    uint32              setpcmisses;    /* setting/adding property pc misses */
    uint32              setmisses;      /* JSOP_SET{NAME,PROP} total misses */
    uint32              kpcmisses;      /* slow-path key id == atom misses */
    uint32              kshapemisses;   /* slow-path key object misses */
    uint32              vcapmisses;     /* value capability misses */
    uint32              misses;         /* cache misses */
    uint32              flushes;        /* cache flushes */
    uint32              pcpurges;       /* shadowing purges on proto chain */
  private:
# define PCMETER(x)     x
#else
# define PCMETER(x)     ((void)0)
#endif

    /*
     * Add kshape rather than xor it to avoid collisions between nearby bytecode
     * that are evolving an object by setting successive properties, incrementing
     * the object's scope->shape on each set.
     */
    static inline jsuword
    hash(jsbytecode *pc, jsuword kshape)
    {
        return ((((jsuword(pc) >> SIZE_LOG2) ^ jsuword(pc)) + kshape) & MASK);
    }

    static inline bool matchShape(JSContext *cx, JSObject *obj, uint32 shape);

    JS_REQUIRES_STACK JSAtom *fullTest(JSContext *cx, jsbytecode *pc, JSObject **objp,
                                       JSObject **pobjp, PropertyCacheEntry *entry);

#ifdef DEBUG
    void assertEmpty();
#else
    inline void assertEmpty() {}
#endif

  public:
    JS_ALWAYS_INLINE JS_REQUIRES_STACK void test(JSContext *cx, jsbytecode *pc,
                                                 JSObject *&obj, JSObject *&pobj,
                                                 PropertyCacheEntry *&entry, JSAtom *&atom);

    /*
     * Test for cached information about a property set on *objp at pc.
     *
     * On a fast hit, set *entryp to the entry and return true.
     *
     * On a slow hit, set *entryp to the entry, set *obj2p to the object that
     * owns the property (either obj or a prototype), set *atomp to NULL, and
     * return false.
     *
     * On a miss, set *atomp to the name of the property being set and return false.
     */
    JS_ALWAYS_INLINE bool testForSet(JSContext *cx, jsbytecode *pc, JSObject *obj,
                                     PropertyCacheEntry **entryp, JSObject **obj2p,
                                     JSAtom **atomp);

    /*
     * Test for cached information about creating a new own data property on obj at pc.
     *
     * On a hit, set *spropp to an sprop from the property tree describing the
     * new property as well as all existing properties on obj and return
     * true. Otherwise return false.
     *
     * Hit or miss, *entryp receives a pointer to the property cache entry.
     */
    JS_ALWAYS_INLINE bool testForInit(JSRuntime *rt, jsbytecode *pc, JSObject *obj, JSScope *scope,
                                      JSScopeProperty **spropp, PropertyCacheEntry **entryp);

    /*
     * Fill property cache entry for key cx->fp->pc, optimized value word
     * computed from obj and sprop, and entry capability forged from 24-bit
     * obj->shape(), 4-bit scopeIndex, and 4-bit protoIndex.
     *
     * Return the filled cache entry or JS_NO_PROP_CACHE_FILL if caching was
     * not possible.
     */
    JS_REQUIRES_STACK PropertyCacheEntry *fill(JSContext *cx, JSObject *obj, uintN scopeIndex,
                                               uintN protoIndex, JSObject *pobj,
                                               JSScopeProperty *sprop, JSBool adding = false);

    void purge(JSContext *cx);
    void purgeForScript(JSScript *script);
};

} /* namespace js */

#endif /* jspropertycache_h___ */