reg_alloc.c

/*
 * Copyright (C) 2003-2011, Parrot Foundation.
*/

/*

=head1 NAME

compilers/imcc/reg_alloc.c

=head1 DESCRIPTION

Register allocator:

This is a brute force register allocator. It uses a graph-coloring
algorithm, but the implementation is very kludgy.

It is a partial implementation of a Briggs-style register allocator
The following parts are just missing:

 - Renumbering
 - Coalescing

=head2 Functions

=over 4

=cut

*/

#include <string.h>
#include "imc.h"
#include "optimizer.h"

/* HEADERIZER HFILE: compilers/imcc/imc.h */

/* HEADERIZER BEGIN: static */
/* Don't modify between HEADERIZER BEGIN / HEADERIZER END.  Your changes will be lost. */

static void allocate_lexicals(
    ARGMOD(imc_info_t * imcc),
    ARGMOD(IMC_Unit *unit))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        FUNC_MODIFIES(* imcc)
        FUNC_MODIFIES(*unit);

static void allocate_uniq(
    ARGMOD(imc_info_t * imcc),
    ARGMOD(IMC_Unit *unit),
    int usage)
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        FUNC_MODIFIES(* imcc)
        FUNC_MODIFIES(*unit);

static void build_reglist(ARGMOD(imc_info_t * imcc), ARGMOD(IMC_Unit *unit))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        FUNC_MODIFIES(* imcc)
        FUNC_MODIFIES(*unit);

static void compute_du_chain(ARGMOD(IMC_Unit *unit))
        __attribute__nonnull__(1)
        FUNC_MODIFIES(*unit);

static void compute_one_du_chain(ARGMOD(SymReg *r), ARGIN(IMC_Unit *unit))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        FUNC_MODIFIES(*r);

PARROT_WARN_UNUSED_RESULT
static unsigned int first_avail(
    ARGMOD(imc_info_t * imcc),
    ARGIN(const IMC_Unit *unit),
    int reg_set,
    ARGOUT_NULLOK(Set **avail))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        FUNC_MODIFIES(* imcc)
        FUNC_MODIFIES(*avail);

static void imc_stat_init(ARGMOD(IMC_Unit *unit))
        __attribute__nonnull__(1)
        FUNC_MODIFIES(*unit);

static void make_stat(
    ARGMOD(IMC_Unit *unit),
    ARGMOD_NULLOK(int *sets),
    ARGMOD_NULLOK(int *cols))
        __attribute__nonnull__(1)
        FUNC_MODIFIES(*unit)
        FUNC_MODIFIES(*sets)
        FUNC_MODIFIES(*cols);

static void print_stat(ARGMOD(imc_info_t * imcc), ARGMOD(IMC_Unit *unit))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        FUNC_MODIFIES(* imcc)
        FUNC_MODIFIES(*unit);

PARROT_WARN_UNUSED_RESULT
static int reg_sort_f(ARGIN(const void *a), ARGIN(const void *b))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2);

static void sort_reglist(ARGMOD(IMC_Unit *unit))
        __attribute__nonnull__(1)
        FUNC_MODIFIES(*unit);

static void vanilla_reg_alloc(
    ARGMOD(imc_info_t * imcc),
    ARGMOD(IMC_Unit *unit))
        __attribute__nonnull__(1)
        __attribute__nonnull__(2)
        FUNC_MODIFIES(* imcc)
        FUNC_MODIFIES(*unit);

#define ASSERT_ARGS_allocate_lexicals __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(imcc) \
    , PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_allocate_uniq __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(imcc) \
    , PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_build_reglist __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(imcc) \
    , PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_compute_du_chain __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_compute_one_du_chain __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(r) \
    , PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_first_avail __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(imcc) \
    , PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_imc_stat_init __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_make_stat __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_print_stat __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(imcc) \
    , PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_reg_sort_f __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(a) \
    , PARROT_ASSERT_ARG(b))
#define ASSERT_ARGS_sort_reglist __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(unit))
#define ASSERT_ARGS_vanilla_reg_alloc __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
       PARROT_ASSERT_ARG(imcc) \
    , PARROT_ASSERT_ARG(unit))
/* Don't modify between HEADERIZER BEGIN / HEADERIZER END.  Your changes will be lost. */
/* HEADERIZER END: static */

/*

=item C<void imc_reg_alloc(imc_info_t * imcc, IMC_Unit *unit)>

imc_reg_alloc is the main loop of the allocation algorithm. It operates
on a single compilation unit at a time.

=cut

*/

void
imc_reg_alloc(ARGMOD(imc_info_t * imcc), ARGIN_NULLOK(IMC_Unit *unit))
{
    ASSERT_ARGS(imc_reg_alloc)
    const char *function;

    if (!unit)
        return;

    if (!unit->instructions)
        return;

    imc_stat_init(unit);
    if (!(imcc->optimizer_level & (OPT_PRE|OPT_CFG|OPT_PASM)) && unit->pasm_file)
        goto done;

    if (unit->instructions->symreg_count)
      function = unit->instructions->symregs[0]->name;
    else
      function = "(not a sub)";

    IMCC_debug(imcc, DEBUG_IMC, "\n------------------------\n");
    IMCC_debug(imcc, DEBUG_IMC, "processing sub %s\n", function);
    IMCC_debug(imcc, DEBUG_IMC, "------------------------\n\n");

    if (imcc->optimizer_level == OPT_PRE && unit->pasm_file) {
        while (pre_optimize(imcc, unit))
            ;
        goto done;
    }

    /* all lexicals get a unique register */
    allocate_lexicals(imcc, unit);

    /* build CFG and life info, and optimize iteratively */
    do {
        int first = 1;
        do {
            while (pre_optimize(imcc, unit)) { };

            find_basic_blocks(imcc, unit, first);
            build_cfg(imcc, unit);
            first = 0;
        } while (cfg_optimize(imcc, unit));

        compute_dominators(imcc, unit);
        find_loops(imcc, unit);

        if (imcc->optimizer_level)
            compute_dominance_frontiers(imcc, unit);

        build_reglist(imcc, unit);

        allocate_uniq(imcc, unit, 0);
    } while (!imcc->dont_optimize && optimize(imcc, unit));

    if (imcc->debug & DEBUG_IMC)
        dump_symreg(unit);

    /* TODO add option for a better allocator */
    vanilla_reg_alloc(imcc, unit);

    if (imcc->debug & DEBUG_IMC)
        dump_instructions(imcc, unit);

  done:
    if (imcc->verbose  || (imcc->debug & DEBUG_IMC))
        print_stat(imcc, unit);
    else
        make_stat(unit, NULL, unit->n_regs_used);
}

/*

=item C<void free_reglist(IMC_Unit *unit)>

Frees the register list associated with a compilation unit.

=cut

*/

void
free_reglist(ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(free_reglist)

    if (unit->reglist) {
        mem_sys_free(unit->reglist);
        unit->reglist   = NULL;
        unit->n_symbols = 0;
    }
}

/*

=item C<static void make_stat(IMC_Unit *unit, int *sets, int *cols)>

some statistics about register usage
printed with --verbose --verbose

=cut

*/

static void
make_stat(ARGMOD(IMC_Unit *unit), ARGMOD_NULLOK(int *sets), ARGMOD_NULLOK(int *cols))
{
    ASSERT_ARGS(make_stat)
    /* register usage summary */
    SymHash * const hsh = &unit->hash;
    unsigned int    i;

    for (i = 0; i < hsh->size; i++) {
        SymReg *r;

        for (r = hsh->data[i]; r; r = r->next) {
            /* should be fine uninitialized, but analysis tools get confused */
            int j = 0;

            if (r->color > unit->max_color)
                unit->max_color = r->color;

            switch (r->set) {
                case 'I': j = 0; break;
                case 'N': j = 1; break;
                case 'S': j = 2; break;
                case 'P': j = 3; break;
                default :        continue;
            }

            if (REG_NEEDS_ALLOC(r)) {
                if (sets)
                    sets[j]++;

                if (cols)
                    if (r->color > cols[j])
                        cols[j] = r->color;
            }
        }
    }

    if (cols) {
        int j;
        for (j = 0; j < 4; j++)
            ++cols[j];
    }
}

/*

=item C<static void imc_stat_init(IMC_Unit *unit)>

registes usage of .pir

=cut

*/

static void
imc_stat_init(ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(imc_stat_init)
    int j;

    make_stat(unit, unit->n_vars_used, NULL);

    for (j = 0; j < 4; j++) {
        unit->n_regs_used[j] = -1;
        unit->first_avail[j] =  0;
    }

    memset(&(unit->ostat), 0, sizeof (unit->ostat));
}

/*

=item C<static void print_stat(imc_info_t * imcc, IMC_Unit *unit)>

and final

=cut

*/

static void
print_stat(ARGMOD(imc_info_t * imcc), ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(print_stat)
    int sets[4] = {0, 0, 0, 0};

    const char * const function =
        unit->instructions->symreg_count
            ? unit->instructions->symregs[0]->name
            : "(not a function)";

    make_stat(unit, sets, unit->n_regs_used);
    IMCC_info(imcc, 1,
            "sub %s:\n\tregisters in .pir:\t I%d, N%d, S%d, P%d\n",
            function,
            unit->n_vars_used[0], unit->n_vars_used[1],
            unit->n_vars_used[2], unit->n_vars_used[3]);
    IMCC_info(imcc, 1,
              "\t%d labels, %d lines deleted, "
              "%d if_branch, %d branch_branch\n",
              unit->ostat.deleted_labels, unit->ostat.deleted_ins,
              unit->ostat.if_branch, unit->ostat.branch_branch);
    IMCC_info(imcc, 1, "\t%d branch_cond_loop\n",
              unit->ostat.branch_cond_loop);
    IMCC_info(imcc, 1, "\t%d used once deleted\n",
              unit->ostat.used_once);
    IMCC_info(imcc, 1, "\t%d invariants_moved\n",
              unit->ostat.invariants_moved);
    IMCC_info(imcc, 1, "\tregisters needed:\t I%d, N%d, S%d, P%d\n",
            sets[0], sets[1], sets[2], sets[3]);
    IMCC_info(imcc, 1,
            "\tregisters in .pasm:\t I%d, N%d, S%d, P%d - %d\n",
            unit->n_regs_used[0], unit->n_regs_used[1],
            unit->n_regs_used[2], unit->n_regs_used[3]);
    IMCC_info(imcc, 1, "\t%d basic_blocks, %d edges\n",
            unit->n_basic_blocks, edge_count(unit));
}

/*

=item C<static int reg_sort_f(const void *a, const void *b)>

sort list by line  nr

=cut

*/

PARROT_WARN_UNUSED_RESULT
static int
reg_sort_f(ARGIN(const void *a), ARGIN(const void *b))
{
    ASSERT_ARGS(reg_sort_f)
    const SymReg * const ra = *(const SymReg * const *)a;
    const SymReg * const rb = *(const SymReg * const *)b;

    if (!ra->first_ins || !rb->first_ins)
        return 0;

    if (ra->first_ins->index < rb->first_ins->index)
        return -1;

    if (ra->first_ins->index == rb->first_ins->index)
        return 0;

    return 1;
}

/*

=item C<static void sort_reglist(IMC_Unit *unit)>

Sort a compilation unit's register list (by line number of first appearance).

=cut

*/

static void
sort_reglist(ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(sort_reglist)
    qsort(unit->reglist, unit->n_symbols, sizeof (SymReg *), reg_sort_f);
}

/*

=item C<static void build_reglist(imc_info_t * imcc, IMC_Unit *unit)>

make a linear list of IDENTs and VARs, set n_symbols
TODO
  split the whole life analysis into 4, one per register kind
  registers of different kind never interfere, but the reglist
  has them all

Registers are now sorted according to the line on which their usage
starts, which means that they are sorted by basic block numbers too.

Run through them and allocate all that don't overlap in one bunch.

=cut

*/

static void
build_reglist(ARGMOD(imc_info_t * imcc), ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(build_reglist)
    SymHash  const *hsh = &unit->hash;
    unsigned int    i, count, unused, n_symbols;

    IMCC_info(imcc, 2, "build_reglist\n");

    /* count symbols */
    if (unit->reglist)
        free_reglist(unit);

    count = unit->hash.entries;
    if (count == 0)
        return;

    unit->reglist = mem_gc_allocate_n_typed(imcc->interp, count, SymReg *);

    for (i = count = 0; i < hsh->size; i++) {
        SymReg *r;
        for (r = hsh->data[i]; r; r = r->next) {
            /* Add each symbol to reglist  */
            if (REG_NEEDS_ALLOC(r))
                unit->reglist[count++] = r;
        }
    }

    unit->n_symbols = n_symbols = count;

    if (imcc->debug & DEBUG_IMC)
        dump_symreg(unit);

    compute_du_chain(unit);

    /* we might have unused symbols here, from optimizations */
    for (i = count = unused = 0; i < n_symbols; i++) {
        if (!unit->reglist[i]->first_ins && !(unit->reglist[i]->usage & U_LEXICAL))
            unused++;
        else if (i == count)
            count++;
        else
            unit->reglist[count++] = unit->reglist[i];
    }

    n_symbols      -= unused;
    unit->n_symbols = n_symbols;

    sort_reglist(unit);
}

/*

=item C<static void compute_du_chain(IMC_Unit *unit)>

Compute a DU-chain for each symbolic in a compilation unit

=cut

*/

static void
compute_du_chain(ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(compute_du_chain)
    Instruction *ins = unit->instructions;
    Instruction *lastbranch = NULL;
    unsigned int i;

    /* Compute last branch in this procedure, update instruction index */
    for (i = 0; ins; ins = ins->next) {
        ins->index = i++;
        if (ins->type == ITBRANCH)
            lastbranch = ins;
    }

    /* Compute du-chains for all symbolics */
    for (i = 0; i < unit->n_symbols; i++) {
        SymReg * const r = unit->reglist[i];
        compute_one_du_chain(r, unit);

        /* what is this used for? -lt */
        if (r->type == VTIDENTIFIER
        &&  lastbranch
        &&  r->last_ins
        &&  r->last_ins->index < lastbranch->index)
            r->last_ins = lastbranch;
    }
}

/*

=item C<static void compute_one_du_chain(SymReg *r, IMC_Unit *unit)>

Compute the DU-chain for one register within the compilation unit.

=cut

*/

static void
compute_one_du_chain(ARGMOD(SymReg *r), ARGIN(IMC_Unit *unit))
{
    ASSERT_ARGS(compute_one_du_chain)
    Instruction * ins;

    /* We cannot rely on computing the value of r->first when parsing,
     * since the situation can be changed at any time by the register
     * allocation algorithm */
    r->first_ins     = NULL;
    r->use_count     = 0;
    r->lhs_use_count = 0;

    for (ins = unit->instructions; ins; ins = ins->next) {
        const int rw = instruction_writes(ins, r);

        if (rw || instruction_reads(ins, r)) {
            if (!r->first_ins)
                r->first_ins = ins;

            r->last_ins = ins;

            if (rw)
                r->lhs_use_count++;

            r->use_count++;

            /* if this symbol is used in a different scope
             * assume usage */
            if (r->reg) {
                r->lhs_use_count++;
                r->use_count++;
            }
        }
    }
}

/*

=item C<static unsigned int first_avail(imc_info_t * imcc, const IMC_Unit *unit,
int reg_set, Set **avail)>

find first available register of the given reg_set

=cut

*/

PARROT_WARN_UNUSED_RESULT
static unsigned int
first_avail(ARGMOD(imc_info_t * imcc), ARGIN(const IMC_Unit *unit), int reg_set,
        ARGOUT_NULLOK(Set **avail))
{
    ASSERT_ARGS(first_avail)
    int n = (int)unit->n_symbols > unit->max_color
                ? (int)unit->n_symbols
                : unit->max_color;
    Set *allocated = set_make(imcc, (unsigned int)n + 1);

    const SymHash * const hsh = &unit->hash;

    unsigned int i, first;

    /* find allocated registers */
    for (i = 0; i < hsh->size; i++) {
        SymReg *r;
        for (r = hsh->data[i]; r; r = r->next) {
            if (r->set == reg_set)
                if (REG_NEEDS_ALLOC(r))
                    if (r->color >= 0)
                        set_add(allocated, (unsigned int)r->color);
        }
    }

    first = set_first_zero(allocated);

    if (avail)
        *avail = allocated;
    else
        set_free(allocated);

    return first;
}


/*

=item C<static void allocate_uniq(imc_info_t * imcc, IMC_Unit *unit, int usage)>

allocate lexicals or non-volatile in ascending order

=cut

*/

static void
allocate_uniq(ARGMOD(imc_info_t * imcc), ARGMOD(IMC_Unit *unit), int usage)
{
    ASSERT_ARGS(allocate_uniq)
    SymHash     *hsh     = &unit->hash;
    Set         *sets[4] = { NULL, NULL, NULL, NULL };
    SymReg      *r;
    unsigned int i;

    for (i = 0; i < hsh->size; i++) {
        for (r = hsh->data[i]; r; r = r->next) {
            int j = -1;

            switch (r->set) {
                case 'I': j = 0; break;
                case 'N': j = 1; break;
                case 'S': j = 2; break;
                case 'P': j = 3; break;
                default :        continue;
            }

            if (REG_NEEDS_ALLOC(r)
                    &&  r->color == -1
                    && (r->usage & usage)
                    && r->use_count) {
                Set         *avail     = sets[j];
                unsigned int first_reg = avail
                                       ? set_first_zero(avail)
                                       : first_avail(imcc, unit, (int)r->set, &avail);
                set_add(avail, first_reg);
                r->color = first_reg++;

                IMCC_debug(imcc, DEBUG_IMC,
                        "allocate %s sym %c '%s'  color %d\n",
                        usage & U_LEXICAL ? "Lexical" : "Non-vol",
                        (int)r->set, r->name, r->color);

                unit->first_avail[j] = first_reg;

                /* don't lose this set; we must free it */
                if (!sets[j])
                    sets[j] = avail;
            }
        }
    }

    for (i = 0; i < 4; ++i) {
        if (sets[i])
            set_free(sets[i]);
    }

    /*
     * TODO create allocation_threshold
     *      if there are less registers than threshold
     *      just allocate all and be done with it
     */
}

/*

=item C<static void vanilla_reg_alloc(imc_info_t * imcc, IMC_Unit *unit)>

Vanilla register allocator - assign every virtual register to an actual
register.

=cut

*/

static void
vanilla_reg_alloc(ARGMOD(imc_info_t * imcc), ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(vanilla_reg_alloc)
    const char   type[] = "INSP";
    SymHash     *hsh    = &unit->hash;
    Set         *avail;
    unsigned int i, j;
    int          reg_set, first_reg;

    /* Clear the pre-assigned colors. */
    for (i = 0; i < hsh->size; i++) {
        SymReg *r;
        for (r = hsh->data[i]; r; r = r->next) {
            /* TODO Ignore non-volatiles */
            if (REG_NEEDS_ALLOC(r))
                r->color = -1;
        }
    }

    /* Assign new colors. */
    for (j = 0; j < 4; j++) {
        reg_set   = type[j];
        first_reg = first_avail(imcc, unit, reg_set, &avail);

        /* XXX Use a different loop variable that doesn't shadow outer i */
        for (i = 0; i < hsh->size; i++) {
            SymReg *r;
            for (r = hsh->data[i]; r; r = r->next) {
                if (r->set != reg_set)
                    continue;
                if (REG_NEEDS_ALLOC(r) && (r->color == -1)) {
                    if (set_contains(avail, first_reg))
                        first_reg = first_avail(imcc, unit, reg_set, NULL);

                    set_add(avail, first_reg);
                    r->color = first_reg++;
                }
            }
        }

        set_free(avail);
        unit->first_avail[j] = first_reg;
    }
}

/*

=item C<static void allocate_lexicals(imc_info_t * imcc, IMC_Unit *unit)>

Allocate registers for lexical variables. These must have unique registers
because they are accessible through the LexPad.

=cut

*/

static void
allocate_lexicals(ARGMOD(imc_info_t * imcc), ARGMOD(IMC_Unit *unit))
{
    ASSERT_ARGS(allocate_lexicals)
    IMCC_debug(imcc, DEBUG_IMC, "allocate lexicals\n");
    allocate_uniq(imcc, unit, U_LEXICAL);
}

/*

=back

=cut

*/

/*
 * Local variables:
 *   c-file-style: "parrot"
 * End:
 * vim: expandtab shiftwidth=4 cinoptions='\:2=2' :
 */