src/third_party/mozjs/js/src/frontend/SourceNotes.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef frontend_SourceNotes_h
#define frontend_SourceNotes_h

#include "jsprvtd.h"

namespace js {

/*
 * Source notes generated along with bytecode for decompiling and debugging.
 * A source note is a uint8_t with 5 bits of type and 3 of offset from the pc
 * of the previous note. If 3 bits of offset aren't enough, extended delta
 * notes (SRC_XDELTA) consisting of 2 set high order bits followed by 6 offset
 * bits are emitted before the next note. Some notes have operand offsets
 * encoded immediately after them, in note bytes or byte-triples.
 *
 *                 Source Note               Extended Delta
 *              +7-6-5-4-3+2-1-0+           +7-6-5+4-3-2-1-0+
 *              |note-type|delta|           |1 1| ext-delta |
 *              +---------+-----+           +---+-----------+
 *
 * At most one "gettable" note (i.e., a note of type other than SRC_NEWLINE,
 * SRC_COLSPAN, SRC_SETLINE, and SRC_XDELTA) applies to a given bytecode.
 *
 * NB: the js_SrcNoteSpec array in BytecodeEmitter.cpp is indexed by this
 * enum, so its initializers need to match the order here.
 *
 * Don't forget to update XDR_BYTECODE_VERSION in vm/Xdr.h for all such
 * incompatible source note or other bytecode changes.
 */
enum SrcNoteType {
    SRC_NULL        = 0,        /* terminates a note vector */

    SRC_IF          = 1,        /* JSOP_IFEQ bytecode is from an if-then */
    SRC_IF_ELSE     = 2,        /* JSOP_IFEQ bytecode is from an if-then-else */
    SRC_COND        = 3,        /* JSOP_IFEQ is from conditional ?: operator */

    SRC_FOR         = 4,        /* JSOP_NOP or JSOP_POP in for(;;) loop head */

    SRC_WHILE       = 5,        /* JSOP_GOTO to for or while loop condition
                                   from before loop, else JSOP_NOP at top of
                                   do-while loop */
    SRC_FOR_IN      = 6,        /* JSOP_GOTO to for-in loop condition from
                                   before loop */
    SRC_CONTINUE    = 7,        /* JSOP_GOTO is a continue */
    SRC_BREAK       = 8,        /* JSOP_GOTO is a break */
    SRC_BREAK2LABEL = 9,        /* JSOP_GOTO for 'break label' */
    SRC_SWITCHBREAK = 10,       /* JSOP_GOTO is a break in a switch */

    SRC_TABLESWITCH = 11,       /* JSOP_TABLESWITCH, offset points to end of
                                   switch */
    SRC_CONDSWITCH  = 12,       /* JSOP_CONDSWITCH, 1st offset points to end of
                                   switch, 2nd points to first JSOP_CASE */

    SRC_NEXTCASE    = 13,       /* distance forward from one CASE in a
                                   CONDSWITCH to the next */

    SRC_ASSIGNOP    = 14,       /* += or another assign-op follows */

    SRC_HIDDEN      = 15,       /* opcode shouldn't be decompiled */

    SRC_CATCH       = 16,       /* catch block has guard */

    /* All notes below here are "gettable".  See SN_IS_GETTABLE below. */
    SRC_LAST_GETTABLE = SRC_CATCH,

    SRC_COLSPAN     = 17,       /* number of columns this opcode spans */
    SRC_NEWLINE     = 18,       /* bytecode follows a source newline */
    SRC_SETLINE     = 19,       /* a file-absolute source line number note */

    SRC_UNUSED20    = 20,
    SRC_UNUSED21    = 21,
    SRC_UNUSED22    = 22,
    SRC_UNUSED23    = 23,

    SRC_XDELTA      = 24        /* 24-31 are for extended delta notes */
};

}  // namespace js

#define SN_TYPE_BITS            5
#define SN_DELTA_BITS           3
#define SN_XDELTA_BITS          6
#define SN_TYPE_MASK            (JS_BITMASK(SN_TYPE_BITS) << SN_DELTA_BITS)
#define SN_DELTA_MASK           ((ptrdiff_t)JS_BITMASK(SN_DELTA_BITS))
#define SN_XDELTA_MASK          ((ptrdiff_t)JS_BITMASK(SN_XDELTA_BITS))

#define SN_MAKE_NOTE(sn,t,d)    (*(sn) = (jssrcnote)                          \
                                          (((t) << SN_DELTA_BITS)             \
                                           | ((d) & SN_DELTA_MASK)))
#define SN_MAKE_XDELTA(sn,d)    (*(sn) = (jssrcnote)                          \
                                          ((SRC_XDELTA << SN_DELTA_BITS)      \
                                           | ((d) & SN_XDELTA_MASK)))

#define SN_IS_XDELTA(sn)        ((*(sn) >> SN_DELTA_BITS) >= SRC_XDELTA)
#define SN_TYPE(sn)             ((js::SrcNoteType)(SN_IS_XDELTA(sn)           \
                                                   ? SRC_XDELTA               \
                                                   : *(sn) >> SN_DELTA_BITS))
#define SN_SET_TYPE(sn,type)    SN_MAKE_NOTE(sn, type, SN_DELTA(sn))
#define SN_IS_GETTABLE(sn)      (SN_TYPE(sn) <= SRC_LAST_GETTABLE)

#define SN_DELTA(sn)            ((ptrdiff_t)(SN_IS_XDELTA(sn)                 \
                                             ? *(sn) & SN_XDELTA_MASK         \
                                             : *(sn) & SN_DELTA_MASK))
#define SN_SET_DELTA(sn,delta)  (SN_IS_XDELTA(sn)                             \
                                 ? SN_MAKE_XDELTA(sn, delta)                  \
                                 : SN_MAKE_NOTE(sn, SN_TYPE(sn), delta))

#define SN_DELTA_LIMIT          ((ptrdiff_t)JS_BIT(SN_DELTA_BITS))
#define SN_XDELTA_LIMIT         ((ptrdiff_t)JS_BIT(SN_XDELTA_BITS))

/*
 * Offset fields follow certain notes and are frequency-encoded: an offset in
 * [0,0x7f] consumes one byte, an offset in [0x80,0x7fffff] takes three, and
 * the high bit of the first byte is set.
 */
#define SN_3BYTE_OFFSET_FLAG    0x80
#define SN_3BYTE_OFFSET_MASK    0x7f

/*
 * Negative SRC_COLSPAN offsets are rare, but can arise with for(;;) loops and
 * other constructs that generate code in non-source order. They can also arise
 * due to failure to update pn->pn_pos.end to be the last child's end -- such
 * failures are bugs to fix.
 *
 * Source note offsets in general must be non-negative and less than 0x800000,
 * per the above SN_3BYTE_* definitions. To encode negative colspans, we bias
 * them by the offset domain size and restrict non-negative colspans to less
 * than half this domain.
 */
#define SN_COLSPAN_DOMAIN       ptrdiff_t(SN_3BYTE_OFFSET_FLAG << 16)

#define SN_MAX_OFFSET ((size_t)((ptrdiff_t)SN_3BYTE_OFFSET_FLAG << 16) - 1)

#define SN_LENGTH(sn)           ((js_SrcNoteSpec[SN_TYPE(sn)].arity == 0) ? 1 \
                                 : js_SrcNoteLength(sn))
#define SN_NEXT(sn)             ((sn) + SN_LENGTH(sn))

/* A source note array is terminated by an all-zero element. */
#define SN_MAKE_TERMINATOR(sn)  (*(sn) = SRC_NULL)
#define SN_IS_TERMINATOR(sn)    (*(sn) == SRC_NULL)

struct JSSrcNoteSpec {
    const char      *name;      /* name for disassembly/debugging output */
    int8_t          arity;      /* number of offset operands */
};

extern JS_FRIEND_DATA(const JSSrcNoteSpec) js_SrcNoteSpec[];
extern JS_FRIEND_API(unsigned)         js_SrcNoteLength(jssrcnote *sn);

/*
 * Get and set the offset operand identified by which (0 for the first, etc.).
 */
extern JS_FRIEND_API(ptrdiff_t)
js_GetSrcNoteOffset(jssrcnote *sn, unsigned which);

#endif /* frontend_SourceNotes_h */