ruby/mjit_compile.c

/**********************************************************************

  mjit_compile.c - MRI method JIT compiler

  Copyright (C) 2017 Takashi Kokubun <takashikkbn@gmail.com>.

**********************************************************************/

// NOTE: All functions in this file are executed on MJIT worker. So don't
// call Ruby methods (C functions that may call rb_funcall) or trigger
// GC (using ZALLOC, xmalloc, xfree, etc.) in this file.

#include "internal.h"

#if USE_MJIT

#include "vm_core.h"
#include "vm_exec.h"
#include "mjit.h"
#include "insns.inc"
#include "insns_info.inc"
#include "vm_insnhelper.h"

// Macros to check if a position is already compiled using compile_status.stack_size_for_pos
#define NOT_COMPILED_STACK_SIZE -1
#define ALREADY_COMPILED_P(status, pos) (status->stack_size_for_pos[pos] != NOT_COMPILED_STACK_SIZE)

// Storage to keep compiler's status.  This should have information
// which is global during one `mjit_compile` call.  Ones conditional
// in each branch should be stored in `compile_branch`.
struct compile_status {
    bool success; // has true if compilation has had no issue
    int *stack_size_for_pos; // stack_size_for_pos[pos] has stack size for the position (otherwise -1)
    // If true, JIT-ed code will use local variables to store pushed values instead of
    // using VM's stack and moving stack pointer.
    bool local_stack_p;
    // Safely-accessible cache entries copied from main thread.
    union iseq_inline_storage_entry *is_entries;
    struct rb_call_cache *cc_entries;
    // Mutated optimization levels
    struct rb_mjit_compile_info *compile_info;
};

// Storage to keep data which is consistent in each conditional branch.
// This is created and used for one `compile_insns` call and its values
// should be copied for extra `compile_insns` call.
struct compile_branch {
    unsigned int stack_size; // this simulates sp (stack pointer) of YARV
    bool finish_p; // if true, compilation in this branch should stop and let another branch to be compiled
};

struct case_dispatch_var {
    FILE *f;
    unsigned int base_pos;
    VALUE last_value;
};

// Returns true if call cache is still not obsoleted and cc->me->def->type is available.
static bool
has_valid_method_type(CALL_CACHE cc)
{
    extern bool mjit_valid_class_serial_p(rb_serial_t class_serial);
    return GET_GLOBAL_METHOD_STATE() == cc->method_state
        && mjit_valid_class_serial_p(cc->class_serial) && cc->me;
}

// Returns true if iseq is inlinable, otherwise NULL. This becomes true in the same condition
// as CC_SET_FASTPATH (in vm_callee_setup_arg) is called from vm_call_iseq_setup.
static bool
inlinable_iseq_p(const CALL_INFO ci, const CALL_CACHE cc, const rb_iseq_t *iseq)
{
    extern bool rb_simple_iseq_p(const rb_iseq_t *iseq);
    return iseq != NULL
        && !(ci->flag & VM_CALL_KW_SPLAT) && rb_simple_iseq_p(iseq) // Top of vm_callee_setup_arg. In this case, opt_pc is 0.
        && ci->orig_argc == iseq->body->param.lead_num // exclude argument_arity_error (assumption: `calling->argc == ci->orig_argc` in send insns)
        && vm_call_iseq_optimizable_p(ci, cc); // CC_SET_FASTPATH condition
}

static int
compile_case_dispatch_each(VALUE key, VALUE value, VALUE arg)
{
    struct case_dispatch_var *var = (struct case_dispatch_var *)arg;
    unsigned int offset;

    if (var->last_value != value) {
        offset = FIX2INT(value);
        var->last_value = value;
        fprintf(var->f, "      case %d:\n", offset);
        fprintf(var->f, "        goto label_%d;\n", var->base_pos + offset);
        fprintf(var->f, "        break;\n");
    }
    return ST_CONTINUE;
}

// Calling rb_id2str in MJIT worker causes random SEGV. So this is disabled by default.
static void
comment_id(FILE *f, ID id)
{
#ifdef MJIT_COMMENT_ID
    VALUE name = rb_id2str(id);
    const char *p, *e;
    char c, prev = '\0';

    if (!name) return;
    p = RSTRING_PTR(name);
    e = RSTRING_END(name);
    fputs("/* :\"", f);
    for (; p < e; ++p) {
        switch (c = *p) {
          case '*': case '/': if (prev != (c ^ ('/' ^ '*'))) break;
          case '\\': case '"': fputc('\\', f);
        }
        fputc(c, f);
        prev = c;
    }
    fputs("\" */", f);
#endif
}

static void compile_insns(FILE *f, const struct rb_iseq_constant_body *body, unsigned int stack_size,
                          unsigned int pos, struct compile_status *status);

// Main function of JIT compilation, vm_exec_core counterpart for JIT. Compile one insn to `f`, may modify
// b->stack_size and return next position.
//
// When you add a new instruction to insns.def, it would be nice to have JIT compilation support here but
// it's optional. This JIT compiler just ignores ISeq which includes unknown instruction, and ISeq which
// does not have it can be compiled as usual.
static unsigned int
compile_insn(FILE *f, const struct rb_iseq_constant_body *body, const int insn, const VALUE *operands,
             const unsigned int pos, struct compile_status *status, struct compile_branch *b)
{
    unsigned int next_pos = pos + insn_len(insn);

/*****************/
 #include "mjit_compile.inc"
/*****************/

    // If next_pos is already compiled and this branch is not finished yet,
    // next instruction won't be compiled in C code next and will need `goto`.
    if (!b->finish_p && next_pos < body->iseq_size && ALREADY_COMPILED_P(status, next_pos)) {
        fprintf(f, "goto label_%d;\n", next_pos);

        // Verify stack size assumption is the same among multiple branches
        if ((unsigned int)status->stack_size_for_pos[next_pos] != b->stack_size) {
            if (mjit_opts.warnings || mjit_opts.verbose)
                fprintf(stderr, "MJIT warning: JIT stack assumption is not the same between branches (%d != %u)\n",
                        status->stack_size_for_pos[next_pos], b->stack_size);
            status->success = false;
        }
    }

    return next_pos;
}

// Compile one conditional branch.  If it has branchXXX insn, this should be
// called multiple times for each branch.
static void
compile_insns(FILE *f, const struct rb_iseq_constant_body *body, unsigned int stack_size,
              unsigned int pos, struct compile_status *status)
{
    int insn;
    struct compile_branch branch;

    branch.stack_size = stack_size;
    branch.finish_p = false;

    while (pos < body->iseq_size && !ALREADY_COMPILED_P(status, pos) && !branch.finish_p) {
#if OPT_DIRECT_THREADED_CODE || OPT_CALL_THREADED_CODE
        insn = rb_vm_insn_addr2insn((void *)body->iseq_encoded[pos]);
#else
        insn = (int)body->iseq_encoded[pos];
#endif
        status->stack_size_for_pos[pos] = (int)branch.stack_size;

        fprintf(f, "\nlabel_%d: /* %s */\n", pos, insn_name(insn));
        pos = compile_insn(f, body, insn, body->iseq_encoded + (pos+1), pos, status, &branch);
        if (status->success && branch.stack_size > body->stack_max) {
            if (mjit_opts.warnings || mjit_opts.verbose)
                fprintf(stderr, "MJIT warning: JIT stack size (%d) exceeded its max size (%d)\n", branch.stack_size, body->stack_max);
            status->success = false;
        }
        if (!status->success)
            break;
    }
}

// Print the block to cancel JIT execution.
static void
compile_cancel_handler(FILE *f, const struct rb_iseq_constant_body *body, struct compile_status *status)
{
    unsigned int i;

    fprintf(f, "\nsend_cancel:\n");
    fprintf(f, "    RB_DEBUG_COUNTER_INC(mjit_cancel_send_inline);\n");
    fprintf(f, "    rb_mjit_iseq_compile_info(original_iseq->body)->disable_send_cache = true;\n");
    fprintf(f, "    rb_mjit_recompile_iseq(original_iseq);\n");
    fprintf(f, "    goto cancel;\n");

    fprintf(f, "\nivar_cancel:\n");
    fprintf(f, "    RB_DEBUG_COUNTER_INC(mjit_cancel_ivar_inline);\n");
    fprintf(f, "    rb_mjit_iseq_compile_info(original_iseq->body)->disable_ivar_cache = true;\n");
    fprintf(f, "    rb_mjit_recompile_iseq(original_iseq);\n");
    fprintf(f, "    goto cancel;\n");

    fprintf(f, "\ncancel:\n");
    fprintf(f, "    RB_DEBUG_COUNTER_INC(mjit_cancel);\n");
    if (status->local_stack_p) {
        for (i = 0; i < body->stack_max; i++) {
            fprintf(f, "    *(vm_base_ptr(reg_cfp) + %d) = stack[%d];\n", i, i);
        }
    }
    fprintf(f, "    return Qundef;\n");
}

extern bool mjit_copy_cache_from_main_thread(const rb_iseq_t *iseq, struct rb_call_cache *cc_entries, union iseq_inline_storage_entry *is_entries);

static bool
mjit_compile_body(FILE *f, const rb_iseq_t *iseq)
{
    const struct rb_iseq_constant_body *body = iseq->body;
    struct compile_status status = {
        .success = true,
        .local_stack_p = !body->catch_except_p,
        .stack_size_for_pos = (int *)alloca(sizeof(int) * body->iseq_size),
        .cc_entries = (body->ci_size + body->ci_kw_size) > 0 ?
            alloca(sizeof(struct rb_call_cache) * (body->ci_size + body->ci_kw_size)) : NULL,
        .is_entries = (body->is_size > 0) ?
            alloca(sizeof(union iseq_inline_storage_entry) * body->is_size) : NULL,
        .compile_info = rb_mjit_iseq_compile_info(body),
    };
    memset(status.stack_size_for_pos, NOT_COMPILED_STACK_SIZE, sizeof(int) * body->iseq_size);
    if ((status.cc_entries != NULL || status.is_entries != NULL)
            && !mjit_copy_cache_from_main_thread(iseq, status.cc_entries, status.is_entries))
        return false;

    if (status.local_stack_p) {
        fprintf(f, "    VALUE stack[%d];\n", body->stack_max);
    }
    else {
        fprintf(f, "    VALUE *stack = reg_cfp->sp;\n");
    }
    fprintf(f, "    static const rb_iseq_t *original_iseq = 0x%"PRIxVALUE";\n", (VALUE)iseq);
    fprintf(f, "    static const VALUE *const original_body_iseq = (VALUE *)0x%"PRIxVALUE";\n",
            (VALUE)body->iseq_encoded);

    // Simulate `opt_pc` in setup_parameters_complex. Other PCs which may be passed by catch tables
    // are not considered since vm_exec doesn't call mjit_exec for catch tables.
    if (body->param.flags.has_opt) {
        int i;
        fprintf(f, "\n");
        fprintf(f, "    switch (reg_cfp->pc - reg_cfp->iseq->body->iseq_encoded) {\n");
        for (i = 0; i <= body->param.opt_num; i++) {
            VALUE pc_offset = body->param.opt_table[i];
            fprintf(f, "      case %"PRIdVALUE":\n", pc_offset);
            fprintf(f, "        goto label_%"PRIdVALUE";\n", pc_offset);
        }
        fprintf(f, "    }\n");
    }

    compile_insns(f, body, 0, 0, &status);
    compile_cancel_handler(f, body, &status);
    return status.success;
}

// Compile ISeq to C code in `f`. It returns true if it succeeds to compile.
bool
mjit_compile(FILE *f, const rb_iseq_t *iseq, const char *funcname)
{
    // For performance, we verify stack size only on compilation time (mjit_compile.inc.erb) without --jit-debug
    if (!mjit_opts.debug) {
        fprintf(f, "#undef OPT_CHECKED_RUN\n");
        fprintf(f, "#define OPT_CHECKED_RUN 0\n\n");
    }

#ifdef _WIN32
    fprintf(f, "__declspec(dllexport)\n");
#endif
    fprintf(f, "VALUE\n%s(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp)\n{\n", funcname);
    bool result = mjit_compile_body(f, iseq);
    fprintf(f, "\n} // end of %s\n", funcname);
    return result;
}

#endif // USE_MJIT