shithub: mc

ref: 94acc736ec2d8d80533439a24742d7c796aaab4f
dir: /mi/fold.c/

#include <stdlib.h>
#include <stdio.h>
#include <inttypes.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 "mi.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(Srcloc loc, vlong val, Type *t)
{
    Node *l, *n;

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

static int issmallconst(Node *dcl)
{
    Type *t;

    if (!dcl->decl.isconst)
        return 0;
    if (!dcl->decl.init)
        return 0;
    t = tybase(exprtype(dcl->decl.init));
    if (t->type <= Tyflt64)
        return 1;
    return 0;
}

static Node *foldcast(Node *n)
{
    Type *to, *from;
    Node *sub;

    sub = n->expr.args[0];
    to = exprtype(n);
    from = exprtype(sub);

    switch (tybase(to)->type) {
        case Tybool:
        case Tyint8: case Tyint16: case Tyint32: case Tyint64:
        case Tyuint8: case Tyuint16: case Tyuint32: case Tyuint64:
        case Tyint: case Tyuint: case Tylong: case Tyulong:
        case Tychar: case Tybyte:
        case Typtr:
            switch (tybase(from)->type) {
                case Tybool:
                case Tyint8: case Tyint16: case Tyint32: case Tyint64:
                case Tyuint8: case Tyuint16: case Tyuint32: case Tyuint64:
                case Tyint: case Tyuint: case Tylong: case Tyulong:
                case Tychar: case Tybyte:
                case Typtr:
                    if (exprop(sub) == Olit || tybase(from)->type == tybase(to)->type) {
                        sub->expr.type = to;
                        return sub;
                    } else {
                        return n;
                    }
                default:
                    return n;
            }
        default:
            return n;
    }
    return n;
}



Node *fold(Node *n, int foldvar)
{
    Node **args, *r;
    Type *t;
    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], foldvar);
    switch (exprop(n)) {
        case Ovar:
            if (foldvar && issmallconst(decls[n->expr.did]))
                r = fold(decls[n->expr.did]->decl.init, foldvar);
            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->loc, 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->loc, 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->loc, a * b, exprtype(n));
            break;
        case Odiv:
            /* x/0 = error */
            if (isval(args[1], 0))
                fatal(args[1], "division by zero");
            /* 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->loc, 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->loc, a % b, exprtype(n));
            break;
        case Oneg:
            if (islit(args[0], &a))
                r = val(n->loc, -a, exprtype(n));
            break;
        case Obsl:
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->loc, a << b, exprtype(n));
            break;
        case Obsr:
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->loc, a >> b, exprtype(n));
            break;
        case Obor:
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->loc, a | b, exprtype(n));
            break;
        case Oband:
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->loc, a & b, exprtype(n));
            break;
        case Obxor:
            if (islit(args[0], &a) && islit(args[1], &b))
                r = val(n->loc, a ^ b, exprtype(n));
            break;
        case Omemb:
            t = tybase(exprtype(args[0]));
            /* we only fold lengths right now */
            if (t->type == Tyarray && !strcmp(namestr(args[1]), "len"))
                r = t->asize;
            break;
        case Ocast:
            r = foldcast(n);
            break;
        default:
            break;
    }

    if (r && n->expr.idx)
      r->expr.idx = n->expr.idx;

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