shithub: mc

ref: 0116ef24cb193165de85d3a707d4dbd64ba1b60f
dir: /opt/fold.c/

#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <stdarg.h>
#include <ctype.h>
#include <string.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "parse.h"
#include "opt.h"

static int islit(Node *n, vlong *v)
{
    Node *l;

    if (exprop(n) != Olit)
        return 0;
    l = n->expr.args[0];
    if (l->lit.littype != Lint)
        return 0;
    *v = l->lit.intval;
    return 1;
}

static int isval(Node *n, vlong val)
{
    vlong v;

    if (!islit(n, &v))
        return 0;
    return v == val;
}

static Node *val(int line, vlong val, Type *t)
{
    Node *n;

    n = mkint(line, val);
    n = mkexpr(line, Olit, n, NULL);
    n->expr.type = t;
    return n;
}

Node *fold(Node *n)
{
    Node **args, *r;
    vlong a, b;
    size_t i;

    if (!n)
        return NULL;
    if (n->type != Nexpr)
        return n;

    r = NULL;
    args = n->expr.args;
    for (i = 0; i < n->expr.nargs; i++)
        args[i] = fold(args[i]);
    switch (exprop(n)) {
        case Ovar:
            /* FIXME: chase small consts */
            break;
        case Oadd:
            /* x + 0 = 0 */
            if (isval(args[0], 0))
                r = args[1];
            if (isval(args[1], 0))
                r = args[0];
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->line, a + b, exprtype(n));
            break;
        case Osub:
            /* x - 0 = 0 */
            if (isval(args[1], 0))
                r = args[0];
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->line, a - b, exprtype(n));
            break;
        case Omul:
            /* 1 * x = x */
            if (isval(args[0], 1))
                r = args[1];
            if (isval(args[1], 1))
                r = args[0];
            /* 0 * x = 0 */
            if (isval(args[0], 0))
                r = args[0];
            if (isval(args[1], 0))
                r = args[1];
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->line, a * b, exprtype(n));
            break;
        case Odiv:
            /* x/1 = x */
            if (isval(args[1], 1))
                r = args[0];
            /* 0/x = 0 */
            if (isval(args[1], 0))
                r = args[1];
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->line, a / b, exprtype(n));
            break;
        case Omod:
            /* x%1 = x */
            if (isval(args[1], 0))
                r = args[0];
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->line, a % b, exprtype(n));
            break;
        case Oneg:
            if (islit(args[0], &a))
                r = val(n->line, -a, exprtype(n));
            break;
        case Ocast:
            /* FIXME: we currentl assume that the bits of the
             * val are close enough. */
            r = args[0];
            r->expr.type = exprtype(n);
            break;
        default:
            break;
    }

    if (r)
        return r;
    else
        return n;
}