i386-asm.c

tiny c compiler

        op = &operands[i];
        str = op->constraint;
        str = skip_constraint_modifiers(str);
        if (isnum(*str) || *str == '[') {
            /* this is a reference to another constraint */
            k = find_constraint(operands, nb_operands, str, NULL);
            if ((unsigned)k >= i || i < nb_outputs)
                error("invalid reference in constraint %d ('%s')",
                      i, str);
            op->ref_index = k;
            if (operands[k].input_index >= 0)
                error("cannot reference twice the same operand");
            operands[k].input_index = i;
            op->priority = 5;
        } else {
            op->priority = constraint_priority(str);
        }
    }
    
    /* sort operands according to their priority */
    for(i=0;i<nb_operands;i++)
        sorted_op[i] = i;
    for(i=0;i<nb_operands - 1;i++) {
        for(j=i+1;j<nb_operands;j++) {
            p1 = operands[sorted_op[i]].priority; 
            p2 = operands[sorted_op[j]].priority;
            if (p2 < p1) {
                tmp = sorted_op[i];
                sorted_op[i] = sorted_op[j];
                sorted_op[j] = tmp;
            }
        }
    }

    for(i = 0;i < NB_ASM_REGS; i++) {
        if (clobber_regs[i])
            regs_allocated[i] = REG_IN_MASK | REG_OUT_MASK;
        else
            regs_allocated[i] = 0;
    }
    /* esp cannot be used */
    regs_allocated[4] = REG_IN_MASK | REG_OUT_MASK; 
    /* ebp cannot be used yet */
    regs_allocated[5] = REG_IN_MASK | REG_OUT_MASK; 

    /* allocate registers and generate corresponding asm moves */
    for(i=0;i<nb_operands;i++) {
        j = sorted_op[i];
        op = &operands[j];
        str = op->constraint;
        /* no need to allocate references */
        if (op->ref_index >= 0)
            continue;
        /* select if register is used for output, input or both */
        if (op->input_index >= 0) {
            reg_mask = REG_IN_MASK | REG_OUT_MASK;
        } else if (j < nb_outputs) {
            reg_mask = REG_OUT_MASK;
        } else {
            reg_mask = REG_IN_MASK;
        }
    try_next:
        c = *str++;
        switch(c) {
        case '=':
            goto try_next;
        case '+':
            op->is_rw = 1;
            /* FALL THRU */
        case '&':
            if (j >= nb_outputs)
                error("'%c' modifier can only be applied to outputs", c);
            reg_mask = REG_IN_MASK | REG_OUT_MASK;
            goto try_next;
        case 'A':
            /* allocate both eax and edx */
            if (is_reg_allocated(TREG_EAX) || 
                is_reg_allocated(TREG_EDX))
                goto try_next;
            op->is_llong = 1;
            op->reg = TREG_EAX;
            regs_allocated[TREG_EAX] |= reg_mask;
            regs_allocated[TREG_EDX] |= reg_mask;
            break;
        case 'a':
            reg = TREG_EAX;
            goto alloc_reg;
        case 'b':
            reg = 3;
            goto alloc_reg;
        case 'c':
            reg = TREG_ECX;
            goto alloc_reg;
        case 'd':
            reg = TREG_EDX;
            goto alloc_reg;
        case 'S':
            reg = 6;
            goto alloc_reg;
        case 'D':
            reg = 7;
        alloc_reg:
            if (is_reg_allocated(reg))
                goto try_next;
            goto reg_found;
        case 'q':
            /* eax, ebx, ecx or edx */
            for(reg = 0; reg < 4; reg++) {
                if (!is_reg_allocated(reg))
                    goto reg_found;
            }
            goto try_next;
        case 'r':
            /* any general register */
            for(reg = 0; reg < 8; reg++) {
                if (!is_reg_allocated(reg))
                    goto reg_found;
            }
            goto try_next;
        reg_found:
            /* now we can reload in the register */
            op->is_llong = 0;
            op->reg = reg;
            regs_allocated[reg] |= reg_mask;
            break;
        case 'i':
            if (!((op->vt->r & (VT_VALMASK | VT_LVAL)) == VT_CONST))
                goto try_next;
            break;
        case 'I':
        case 'N':
        case 'M':
            if (!((op->vt->r & (VT_VALMASK | VT_LVAL | VT_SYM)) == VT_CONST))
                goto try_next;
            break;
        case 'm':
        case 'g':
            /* nothing special to do because the operand is already in
               memory, except if the pointer itself is stored in a
               memory variable (VT_LLOCAL case) */
            /* XXX: fix constant case */
            /* if it is a reference to a memory zone, it must lie
               in a register, so we reserve the register in the
               input registers and a load will be generated
               later */
            if (j < nb_outputs || c == 'm') {
                if ((op->vt->r & VT_VALMASK) == VT_LLOCAL) {
                    /* any general register */
                    for(reg = 0; reg < 8; reg++) {
                        if (!(regs_allocated[reg] & REG_IN_MASK))
                            goto reg_found1;
                    }
                    goto try_next;
                reg_found1:
                    /* now we can reload in the register */
                    regs_allocated[reg] |= REG_IN_MASK;
                    op->reg = reg;
                    op->is_memory = 1;
                }
            }
            break;
        default:
            error("asm constraint %d ('%s') could not be satisfied", 
                  j, op->constraint);
            break;
        }
        /* if a reference is present for that operand, we assign it too */
        if (op->input_index >= 0) {
            operands[op->input_index].reg = op->reg;
            operands[op->input_index].is_llong = op->is_llong;
        }
    }
    
    /* compute out_reg. It is used to store outputs registers to memory
       locations references by pointers (VT_LLOCAL case) */
    *pout_reg = -1;
    for(i=0;i<nb_operands;i++) {
        op = &operands[i];
        if (op->reg >= 0 && 
            (op->vt->r & VT_VALMASK) == VT_LLOCAL  &&
            !op->is_memory) {
            for(reg = 0; reg < 8; reg++) {
                if (!(regs_allocated[reg] & REG_OUT_MASK))
                    goto reg_found2;
            }
            error("could not find free output register for reloading");
        reg_found2:
            *pout_reg = reg;
            break;
        }
    }
    
    /* print sorted constraints */
#ifdef ASM_DEBUG
    for(i=0;i<nb_operands;i++) {
        j = sorted_op[i];
        op = &operands[j];
        printf("%%%d [%s]: \"%s\" r=0x%04x reg=%d\n", 
               j,                
               op->id ? get_tok_str(op->id, NULL) : "", 
               op->constraint,
               op->vt->r,
               op->reg);
    }
    if (*pout_reg >= 0)
        printf("out_reg=%d\n", *pout_reg);
#endif
}

static void subst_asm_operand(CString *add_str, 
                              SValue *sv, int modifier)
{
    int r, reg, size, val;
    char buf[64];

    r = sv->r;
    if ((r & VT_VALMASK) == VT_CONST) {
        if (!(r & VT_LVAL) && modifier != 'c' && modifier != 'n')
            cstr_ccat(add_str, '$');
        if (r & VT_SYM) {
            cstr_cat(add_str, get_tok_str(sv->sym->v, NULL));
            if (sv->c.i != 0) {
                cstr_ccat(add_str, '+');
            } else {
                return;
            }
        }
        val = sv->c.i;
        if (modifier == 'n')
            val = -val;
        snprintf(buf, sizeof(buf), "%d", sv->c.i);
        cstr_cat(add_str, buf);
    } else if ((r & VT_VALMASK) == VT_LOCAL) {
        snprintf(buf, sizeof(buf), "%d(%%ebp)", sv->c.i);
        cstr_cat(add_str, buf);
    } else if (r & VT_LVAL) {
        reg = r & VT_VALMASK;
        if (reg >= VT_CONST)
            error("internal compiler error");
        snprintf(buf, sizeof(buf), "(%%%s)", 
                 get_tok_str(TOK_ASM_eax + reg, NULL));
        cstr_cat(add_str, buf);
    } else {
        /* register case */
        reg = r & VT_VALMASK;
        if (reg >= VT_CONST)
            error("internal compiler error");

        /* choose register operand size */
        if ((sv->type.t & VT_BTYPE) == VT_BYTE)
            size = 1;
        else if ((sv->type.t & VT_BTYPE) == VT_SHORT)
            size = 2;
        else
            size = 4;
        if (size == 1 && reg >= 4)
            size = 4;

        if (modifier == 'b') {
            if (reg >= 4)
                error("cannot use byte register");
            size = 1;
        } else if (modifier == 'h') {
            if (reg >= 4)
                error("cannot use byte register");
            size = -1;
        } else if (modifier == 'w') {
            size = 2;
        }

        switch(size) {
        case -1:
            reg = TOK_ASM_ah + reg;
            break;
        case 1:
            reg = TOK_ASM_al + reg;
            break;
        case 2:
            reg = TOK_ASM_ax + reg;
            break;
        default:
            reg = TOK_ASM_eax + reg;
            break;
        }
        snprintf(buf, sizeof(buf), "%%%s", get_tok_str(reg, NULL));
        cstr_cat(add_str, buf);
    }
}

/* generate prolog and epilog code for asm statment */
static void asm_gen_code(ASMOperand *operands, int nb_operands, 
                         int nb_outputs, int is_output,
                         uint8_t *clobber_regs,
                         int out_reg)
{
    uint8_t regs_allocated[NB_ASM_REGS];
    ASMOperand *op;
    int i, reg;
    static uint8_t reg_saved[NB_SAVED_REGS] = { 3, 6, 7 };

    /* mark all used registers */
    memcpy(regs_allocated, clobber_regs, sizeof(regs_allocated));
    for(i = 0; i < nb_operands;i++) {
        op = &operands[i];
        if (op->reg >= 0)
            regs_allocated[op->reg] = 1;
    }
    if (!is_output) {
        /* generate reg save code */
        for(i = 0; i < NB_SAVED_REGS; i++) {
            reg = reg_saved[i];
            if (regs_allocated[reg]) 
                g(0x50 + reg);
        }

        /* generate load code */
        for(i = 0; i < nb_operands; i++) {
            op = &operands[i];
            if (op->reg >= 0) {
                if ((op->vt->r & VT_VALMASK) == VT_LLOCAL &&
                    op->is_memory) {
                    /* memory reference case (for both input and
                       output cases) */
                    SValue sv;
                    sv = *op->vt;
                    sv.r = (sv.r & ~VT_VALMASK) | VT_LOCAL;
                    load(op->reg, &sv);
                } else if (i >= nb_outputs || op->is_rw) {
                    /* load value in register */
                    load(op->reg, op->vt);
                    if (op->is_llong) {
                        SValue sv;
                        sv = *op->vt;
                        sv.c.ul += 4;
                        load(TREG_EDX, &sv);
                    }
                }
            }
        }
    } else {
        /* generate save code */
        for(i = 0 ; i < nb_outputs; i++) {
            op = &operands[i];
            if (op->reg >= 0) {
                if ((op->vt->r & VT_VALMASK) == VT_LLOCAL) {
                    if (!op->is_memory) {
                        SValue sv;
                        sv = *op->vt;
                        sv.r = (sv.r & ~VT_VALMASK) | VT_LOCAL;
                        load(out_reg, &sv);

                        sv.r = (sv.r & ~VT_VALMASK) | out_reg;
                        store(op->reg, &sv);
                    }
                } else {
                    store(op->reg, op->vt);
                    if (op->is_llong) {
                        SValue sv;
                        sv = *op->vt;
                        sv.c.ul += 4;
                        store(TREG_EDX, &sv);
                    }
                }
            }
        }
        /* generate reg restore code */
        for(i = NB_SAVED_REGS - 1; i >= 0; i--) {
            reg = reg_saved[i];
            if (regs_allocated[reg]) 
                g(0x58 + reg);
        }
    }
}

static void asm_clobber(uint8_t *clobber_regs, const char *str)
{
    int reg;
    TokenSym *ts;

    if (!strcmp(str, "memory") || 
        !strcmp(str, "cc"))
        return;
    ts = tok_alloc(str, strlen(str));
    reg = ts->tok;
    if (reg >= TOK_ASM_eax && reg <= TOK_ASM_edi) {
        reg -= TOK_ASM_eax;
    } else if (reg >= TOK_ASM_ax && reg <= TOK_ASM_di) {
        reg -= TOK_ASM_ax;
    } else {
        error("invalid clobber register '%s'", str);
    }
    clobber_regs[reg] = 1;
}