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iverilog/tgt-vhdl/expr.cc

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/*
* VHDL code generation for expressions.
*
* Copyright (C) 2008-2013 Nick Gasson (nick@nickg.me.uk)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "vhdl_target.h"
#include "support.hh"
#include "state.hh"
#include <iostream>
#include <cassert>
#include <cstring>
/*
* Change the signedness of a vector.
*/
static vhdl_expr *change_signedness(vhdl_expr *e, bool issigned)
{
int msb = e->get_type()->get_msb();
int lsb = e->get_type()->get_lsb();
vhdl_type u(issigned ? VHDL_TYPE_SIGNED : VHDL_TYPE_UNSIGNED, msb, lsb);
return e->cast(&u);
}
/*
* Generate code to ensure that the VHDL expression vhd_e has the
* same signedness as the Verilog expression vl_e.
*/
static vhdl_expr *correct_signedness(vhdl_expr *vhd_e, ivl_expr_t vl_e)
{
bool should_be_signed = ivl_expr_signed(vl_e) != 0;
if (vhd_e->get_type()->get_name() == VHDL_TYPE_UNSIGNED
&& should_be_signed) {
//operand->print();
//std::cout << "^ should be signed but is not" << std::endl;
return change_signedness(vhd_e, true);
}
else if (vhd_e->get_type()->get_name() == VHDL_TYPE_SIGNED
&& !should_be_signed) {
//operand->print();
//std::cout << "^ should be unsigned but is not" << std::endl;
return change_signedness(vhd_e, false);
}
else
return vhd_e;
}
/*
* Convert a constant Verilog string to a constant VHDL string.
*/
static vhdl_expr *translate_string(ivl_expr_t e)
{
// TODO: May need to inspect or escape parts of this
const char *str = ivl_expr_string(e);
return new vhdl_const_string(str);
}
/*
* A reference to a signal in an expression. It's assumed that the
* signal has already been defined elsewhere.
*/
static vhdl_var_ref *translate_signal(ivl_expr_t e)
{
ivl_signal_t sig = ivl_expr_signal(e);
const vhdl_scope *scope = find_scope_for_signal(sig);
assert(scope);
const char *renamed = get_renamed_signal(sig).c_str();
vhdl_decl *decl = scope->get_decl(renamed);
assert(decl);
// Make sure we can read from this declaration
// E.g. if this is an `out' port then we need to make it a buffer
decl->ensure_readable();
// Can't generate a constant initialiser for this signal
// later as it has already been read
if (scope->initializing())
decl->set_initial(NULL);
vhdl_var_ref *ref =
new vhdl_var_ref(renamed, new vhdl_type(*decl->get_type()));
ivl_expr_t off;
if (ivl_signal_array_count(sig) > 0 && (off = ivl_expr_oper1(e))) {
// Select from an array
vhdl_expr *vhd_off = translate_expr(off);
if (NULL == vhd_off) {
delete ref;
return NULL;
}
vhdl_type integer(VHDL_TYPE_INTEGER);
ref->set_slice(vhd_off->cast(&integer));
}
return ref;
}
/*
* A numeric literal ends up as std_logic bit string.
*/
static vhdl_expr *translate_number(ivl_expr_t e)
{
if (ivl_expr_width(e) == 1)
return new vhdl_const_bit(ivl_expr_bits(e)[0]);
else
return new vhdl_const_bits(ivl_expr_bits(e), ivl_expr_width(e),
ivl_expr_signed(e) != 0);
}
static vhdl_expr *translate_ulong(ivl_expr_t e)
{
return new vhdl_const_int(ivl_expr_uvalue(e));
}
static vhdl_expr *translate_delay(ivl_expr_t e)
{
return scale_time(get_active_entity(), ivl_expr_delay_val(e));
}
static vhdl_expr *translate_reduction(support_function_t f, bool neg,
vhdl_expr *operand)
{
vhdl_expr *result;
if (operand->get_type()->get_name() == VHDL_TYPE_STD_LOGIC)
result = operand;
else {
require_support_function(f);
vhdl_fcall *fcall =
new vhdl_fcall(support_function::function_name(f),
vhdl_type::std_logic());
vhdl_type std_logic_vector(VHDL_TYPE_STD_LOGIC_VECTOR);
fcall->add_expr(operand->cast(&std_logic_vector));
result = fcall;
}
if (neg)
return new vhdl_unaryop_expr(VHDL_UNARYOP_NOT, result,
vhdl_type::std_logic());
else
return result;
}
static vhdl_expr *translate_unary(ivl_expr_t e)
{
vhdl_expr *operand = translate_expr(ivl_expr_oper1(e));
if (NULL == operand)
return NULL;
operand = correct_signedness(operand, e);
char opcode = ivl_expr_opcode(e);
switch (opcode) {
case '!':
case '~':
return new vhdl_unaryop_expr
(VHDL_UNARYOP_NOT, operand, new vhdl_type(*operand->get_type()));
case '-':
operand = change_signedness(operand, true);
return new vhdl_unaryop_expr
(VHDL_UNARYOP_NEG, operand, new vhdl_type(*operand->get_type()));
case 'N': // NOR
return translate_reduction(SF_REDUCE_OR, true, operand);
case '|':
return translate_reduction(SF_REDUCE_OR, false, operand);
case 'A': // NAND
return translate_reduction(SF_REDUCE_AND, true, operand);
case '&':
return translate_reduction(SF_REDUCE_AND, false, operand);
case '^': // XOR
return translate_reduction(SF_REDUCE_XOR, false, operand);
case 'X': // XNOR
return translate_reduction(SF_REDUCE_XNOR, false, operand);
default:
error("No translation for unary opcode '%c'\n",
ivl_expr_opcode(e));
delete operand;
return NULL;
}
}
/*
* Translate a numeric binary operator (+, -, etc.) to
* a VHDL equivalent using the numeric_std package.
*/
static vhdl_expr *translate_numeric(vhdl_expr *lhs, vhdl_expr *rhs,
vhdl_binop_t op)
{
// May need to make either side Boolean for operators
// to work
vhdl_type boolean(VHDL_TYPE_BOOLEAN);
if (lhs->get_type()->get_name() == VHDL_TYPE_BOOLEAN)
rhs = rhs->cast(&boolean);
else if (rhs->get_type()->get_name() == VHDL_TYPE_BOOLEAN)
lhs = lhs->cast(&boolean);
vhdl_type *rtype;
if (op == VHDL_BINOP_MULT)
rtype = new vhdl_type(lhs->get_type()->get_name(),
(lhs->get_type()->get_width()*2) - 1, 0);
else
rtype = new vhdl_type(*lhs->get_type());
return new vhdl_binop_expr(lhs, op, rhs, rtype);
}
static vhdl_expr *translate_relation(vhdl_expr *lhs, vhdl_expr *rhs,
vhdl_binop_t op)
{
// Generate any necessary casts
// Arbitrarily, the RHS is casted to the type of the LHS
vhdl_expr *r_cast = rhs->cast(lhs->get_type());
return new vhdl_binop_expr(lhs, op, r_cast, vhdl_type::boolean());
}
/*
* Like translate_relation but both operands must be Boolean.
*/
static vhdl_expr *translate_logical(vhdl_expr *lhs, vhdl_expr *rhs,
vhdl_binop_t op)
{
vhdl_type boolean(VHDL_TYPE_BOOLEAN);
return translate_relation(lhs->cast(&boolean), rhs->cast(&boolean), op);
}
static vhdl_expr *translate_shift(vhdl_expr *lhs, vhdl_expr *rhs,
vhdl_binop_t op)
{
// The RHS must be an integer
vhdl_type integer(VHDL_TYPE_INTEGER);
vhdl_expr *r_cast = rhs->cast(&integer);
vhdl_type *rtype = new vhdl_type(*lhs->get_type());
// The sra operator is not defined on numeric_std types until
// VHDL-2006 which is not well supported. Instead we can use
// the shift_right function which does the same thing and
// exists in earlier versions of numeric_std.
if (op == VHDL_BINOP_SRA) {
vhdl_fcall *sra = new vhdl_fcall("shift_right", rtype);
sra->add_expr(lhs);
sra->add_expr(r_cast);
return sra;
}
else
return new vhdl_binop_expr(lhs, op, r_cast, rtype);
}
/*
* The exponentiation operator in VHDL is not defined for numeric_std
* types. We can get around this by converting the operands to integers,
* performing the operation, then converting the result back to the
* original type. This will work OK in simulation but certainly will not
* synthesise unless the operands are constant.
*
* However, even this does not work quite correctly. The Integer type in
* VHDL is signed and usually only 32 bits, therefore any result larger
* than this will overflow and raise an exception. I can't see a way
* around this at the moment.
*/
static vhdl_expr *translate_power(ivl_expr_t e, vhdl_expr *lhs, vhdl_expr *rhs)
{
vhdl_type integer(VHDL_TYPE_INTEGER);
vhdl_expr *lhs_int = lhs->cast(&integer);
vhdl_expr *rhs_int = rhs->cast(&integer);
vhdl_expr *result = new vhdl_binop_expr(lhs_int, VHDL_BINOP_POWER, rhs_int,
vhdl_type::integer());
int width = ivl_expr_width(e);
const char *func = ivl_expr_signed(e) ? "To_Signed" : "To_Unsigned";
vhdl_type *type = ivl_expr_signed(e)
? vhdl_type::nsigned(width) : vhdl_type::nunsigned(width);
vhdl_fcall *conv = new vhdl_fcall(func, type);
conv->add_expr(result);
conv->add_expr(new vhdl_const_int(width));
return conv;
}
static vhdl_expr *translate_binary(ivl_expr_t e)
{
vhdl_expr *lhs = translate_expr(ivl_expr_oper1(e));
if (NULL == lhs)
return NULL;
vhdl_expr *rhs = translate_expr(ivl_expr_oper2(e));
if (NULL == rhs) {
delete lhs;
return NULL;
}
int lwidth = lhs->get_type()->get_width();
int rwidth = rhs->get_type()->get_width();
int result_width = ivl_expr_width(e);
// There's a funny corner-case where both the LHS and RHS are constant
// single bit numbers and the VHDL compiler can't decide between the
// std_ulogic and bit overloads of various operators
const bool lnumber = ivl_expr_type(ivl_expr_oper1(e)) == IVL_EX_NUMBER;
const bool rnumber = ivl_expr_type(ivl_expr_oper2(e)) == IVL_EX_NUMBER;
if (lwidth == 1 && rwidth == 1 && lnumber && rnumber) {
// It's sufficient to qualify only one side
vhdl_fcall *lqual = new vhdl_fcall("std_logic'", lhs->get_type());
lqual->add_expr(lhs);
lhs = lqual;
}
// For === and !== we need to compare std_logic_vectors
// rather than signeds
vhdl_type std_logic_vector(VHDL_TYPE_STD_LOGIC_VECTOR, result_width-1, 0);
vhdl_type_name_t ltype = lhs->get_type()->get_name();
vhdl_type_name_t rtype = rhs->get_type()->get_name();
bool vectorop =
(ltype == VHDL_TYPE_SIGNED || ltype == VHDL_TYPE_UNSIGNED) &&
(rtype == VHDL_TYPE_SIGNED || rtype == VHDL_TYPE_UNSIGNED);
// May need to resize the left or right hand side or change the
// signedness
if (vectorop) {
if (lwidth < rwidth)
lhs = lhs->resize(rwidth);
else if (rwidth < lwidth)
rhs = rhs->resize(lwidth);
lhs = correct_signedness(lhs, ivl_expr_oper1(e));
rhs = correct_signedness(rhs, ivl_expr_oper2(e));
}
vhdl_expr *result;
switch (ivl_expr_opcode(e)) {
case '+':
result = translate_numeric(lhs, rhs, VHDL_BINOP_ADD);
break;
case '-':
result = translate_numeric(lhs, rhs, VHDL_BINOP_SUB);
break;
case '*':
result = translate_numeric(lhs, rhs, VHDL_BINOP_MULT);
break;
case '/':
result = translate_numeric(lhs, rhs, VHDL_BINOP_DIV);
break;
case '%':
result = translate_numeric(lhs, rhs, VHDL_BINOP_MOD);
break;
case 'e':
result = translate_relation(lhs, rhs, VHDL_BINOP_EQ);
break;
case 'E':
if (vectorop)
result = translate_relation(lhs->cast(&std_logic_vector),
rhs->cast(&std_logic_vector), VHDL_BINOP_EQ);
else
result = translate_relation(lhs, rhs, VHDL_BINOP_EQ);
break;
case 'n':
result = translate_relation(lhs, rhs, VHDL_BINOP_NEQ);
break;
case 'N':
if (vectorop)
result = translate_relation(lhs->cast(&std_logic_vector),
rhs->cast(&std_logic_vector), VHDL_BINOP_NEQ);
else
result = translate_relation(lhs, rhs, VHDL_BINOP_NEQ);
break;
case '&': // Bitwise AND
result = translate_numeric(lhs, rhs, VHDL_BINOP_AND);
break;
case 'a': // Logical AND
result = translate_logical(lhs, rhs, VHDL_BINOP_AND);
break;
case 'A': // Bitwise NAND
result = translate_numeric(lhs, rhs, VHDL_BINOP_NAND);
break;
case 'O': // Bitwise NOR
result = translate_numeric(lhs, rhs, VHDL_BINOP_NOR);
break;
case 'X': // Bitwise XNOR
result = translate_numeric(lhs, rhs, VHDL_BINOP_XNOR);
break;
case '|': // Bitwise OR
result = translate_numeric(lhs, rhs, VHDL_BINOP_OR);
break;
case 'o': // Logical OR
result = translate_logical(lhs, rhs, VHDL_BINOP_OR);
break;
case '<':
result = translate_relation(lhs, rhs, VHDL_BINOP_LT);
break;
case 'L':
result = translate_relation(lhs, rhs, VHDL_BINOP_LEQ);
break;
case '>':
result = translate_relation(lhs, rhs, VHDL_BINOP_GT);
break;
case 'G':
result = translate_relation(lhs, rhs, VHDL_BINOP_GEQ);
break;
case 'l':
result = translate_shift(lhs, rhs, VHDL_BINOP_SL);
break;
case 'r':
result = translate_shift(lhs, rhs, VHDL_BINOP_SR);
break;
case 'R': // Arithmetic right shift
// Verilog only actually performs a signed shift if the
// argument being shifted is signed, otherwise it defaults
// to a normal shift
if (ivl_expr_signed(ivl_expr_oper1(e)))
result = translate_shift(lhs, rhs, VHDL_BINOP_SRA);
else
result = translate_shift(lhs, rhs, VHDL_BINOP_SR);
break;
case '^':
result = translate_numeric(lhs, rhs, VHDL_BINOP_XOR);
break;
case 'p': // Power
result = translate_power(e, lhs, rhs);
break;
default:
error("No translation for binary opcode '%c'\n",
ivl_expr_opcode(e));
delete lhs;
delete rhs;
return NULL;
}
if (NULL == result)
return NULL;
if (vectorop) {
result = correct_signedness(result, e);
int actual_width = result->get_type()->get_width();
if (actual_width != result_width) {
//result->print();
//std::cout << "^ should be " << result_width << " but is " << actual_width << std::endl;
}
}
return result;
}
static vhdl_expr *translate_select(ivl_expr_t e)
{
vhdl_expr *from = translate_expr(ivl_expr_oper1(e));
if (NULL == from)
return NULL;
ivl_expr_t o2 = ivl_expr_oper2(e);
if (o2) {
vhdl_expr *base = translate_expr(ivl_expr_oper2(e));
if (NULL == base)
return NULL;
vhdl_var_ref *from_var_ref = dynamic_cast<vhdl_var_ref*>(from);
if (NULL == from_var_ref) {
// We can't directly select bits from something that's not
// a variable reference in VHDL, but we can emulate the
// effect with a shift and a resize
if (ivl_expr_signed(ivl_expr_oper1(e))) {
vhdl_fcall *sra = new vhdl_fcall("shift_right", from->get_type());
sra->add_expr(from);
sra->add_expr(base->to_integer());
return sra;
}
else
return new vhdl_binop_expr(from, VHDL_BINOP_SR, base->to_integer(),
from->get_type());
}
else if (from_var_ref->get_type()->get_name() != VHDL_TYPE_STD_LOGIC) {
// We can use the more idiomatic VHDL slice notation on a
// single variable reference
vhdl_type integer(VHDL_TYPE_INTEGER);
from_var_ref->set_slice(base->cast(&integer), ivl_expr_width(e) - 1);
return from_var_ref;
}
else {
// Make sure we're not trying to select more than one bit
// from a std_logic (this shouldn't actually happen)
if (ivl_expr_width(e) > 1) {
error("%s:%d: trying to select more than one bit from a std_logic",
ivl_expr_file(e), ivl_expr_lineno(e));
return NULL;
}
else
return from_var_ref;
}
}
else
return correct_signedness(from, e)->resize(ivl_expr_width(e));
}
template <class T>
static T *translate_parms(T *t, ivl_expr_t e)
{
int nparams = ivl_expr_parms(e);
for (int i = 0; i < nparams; i++) {
vhdl_expr *param = translate_expr(ivl_expr_parm(e, i));
if (NULL == param)
return NULL;
t->add_expr(param);
}
return t;
}
static vhdl_expr *translate_ufunc(ivl_expr_t e)
{
ivl_scope_t defscope = ivl_expr_def(e);
ivl_scope_t parentscope = ivl_scope_parent(defscope);
assert(ivl_scope_type(parentscope) == IVL_SCT_MODULE);
// A function is always declared in a module, which should have
// a corresponding entity by this point: so we can get type
// information, etc. from the declaration
vhdl_entity *parent_ent = find_entity(parentscope);
assert(parent_ent);
const char *funcname = ivl_scope_tname(defscope);
vhdl_type *rettype =
vhdl_type::type_for(ivl_expr_width(e), ivl_expr_signed(e) != 0);
vhdl_fcall *fcall = new vhdl_fcall(funcname, rettype);
int nparams = ivl_expr_parms(e);
for (int i = 0; i < nparams; i++) {
vhdl_expr *param = translate_expr(ivl_expr_parm(e, i));
if (NULL == param) {
delete fcall;
return NULL;
}
// Ensure the parameter has the correct VHDL type
// Parameter number is i + 1 since 0th parameter is return value
ivl_signal_t param_sig = ivl_scope_port(defscope, i + 1);
vhdl_type *param_type =
vhdl_type::type_for(ivl_signal_width(param_sig),
ivl_signal_signed(param_sig) != 0);
fcall->add_expr(param->cast(param_type));
delete param_type;
}
return fcall;
}
static vhdl_expr *translate_ternary(ivl_expr_t e)
{
support_function_t sf;
int width = ivl_expr_width(e);
bool issigned = ivl_expr_signed(e) != 0;
if (width == 1)
sf = SF_TERNARY_LOGIC;
else if (issigned)
sf = SF_TERNARY_SIGNED;
else
sf = SF_TERNARY_UNSIGNED;
require_support_function(sf);
vhdl_expr *test = translate_expr(ivl_expr_oper1(e));
vhdl_expr *true_part = translate_expr(ivl_expr_oper2(e));
vhdl_expr *false_part = translate_expr(ivl_expr_oper3(e));
if (!test || !true_part || !false_part)
return NULL;
vhdl_type boolean(VHDL_TYPE_BOOLEAN);
test = test->cast(&boolean);
vhdl_fcall *fcall =
new vhdl_fcall(support_function::function_name(sf),
vhdl_type::type_for(width, issigned));
fcall->add_expr(test);
fcall->add_expr(true_part);
fcall->add_expr(false_part);
return fcall;
}
static vhdl_expr *translate_concat(ivl_expr_t e)
{
vhdl_type *rtype =
vhdl_type::type_for(ivl_expr_width(e), ivl_expr_signed(e) != 0);
vhdl_binop_expr *concat = new vhdl_binop_expr(VHDL_BINOP_CONCAT, rtype);
int nrepeat = ivl_expr_repeat(e);
while (nrepeat--)
translate_parms<vhdl_binop_expr>(concat, e);
return concat;
}
vhdl_expr *translate_sfunc_time(ivl_expr_t)
{
cerr << "warning: no translation for $time (returning 0)" << endl;
vhdl_expr *result = new vhdl_const_int(0);
result->set_comment("$time not supported, returned 0 instead!");
return result;
}
vhdl_expr *translate_sfunc_stime(ivl_expr_t)
{
cerr << "warning: no translation for $stime (returning 0)" << endl;
vhdl_expr *result = new vhdl_const_int(0);
result->set_comment("$stime not supported, returned 0 instead!");
return result;
}
vhdl_expr *translate_sfunc_simtime(ivl_expr_t)
{
cerr << "warning: no translation for $simtime (returning 0)" << endl;
vhdl_expr *result = new vhdl_const_int(0);
result->set_comment("$simtime not supported, returned 0 instead!");
return result;
}
vhdl_expr *translate_sfunc_random(ivl_expr_t)
{
cerr << "warning: no translation for $random (returning 0)" << endl;
vhdl_expr *result = new vhdl_const_int(0);
result->set_comment("$random not supported, returned 0 instead!");
return result;
}
vhdl_expr *translate_sfunc_fopen(ivl_expr_t)
{
cerr << "warning: no translation for $fopen (returning 0)" << endl;
vhdl_expr *result = new vhdl_const_int(0);
result->set_comment("$fopen not supported, returned 0 instead!");
return result;
}
vhdl_expr *translate_sfunc(ivl_expr_t e)
{
const char *name = ivl_expr_name(e);
if (strcmp(name, "$time") == 0)
return translate_sfunc_time(e);
else if (strcmp(name, "$stime") == 0)
return translate_sfunc_stime(e);
else if (strcmp(name, "$simtime") == 0)
return translate_sfunc_simtime(e);
else if (strcmp(name, "$random") == 0)
return translate_sfunc_random(e);
else if (strcmp(name, "$fopen") == 0)
return translate_sfunc_random(e);
else {
error("No translation for system function %s", name);
return NULL;
}
}
/*
* Generate a VHDL expression from a Verilog expression.
*/
vhdl_expr *translate_expr(ivl_expr_t e)
{
assert(e);
ivl_expr_type_t type = ivl_expr_type(e);
switch (type) {
case IVL_EX_STRING:
return translate_string(e);
case IVL_EX_SIGNAL:
return translate_signal(e);
case IVL_EX_NUMBER:
return translate_number(e);
case IVL_EX_ULONG:
return translate_ulong(e);
case IVL_EX_UNARY:
return translate_unary(e);
case IVL_EX_BINARY:
return translate_binary(e);
case IVL_EX_SELECT:
return translate_select(e);
case IVL_EX_UFUNC:
return translate_ufunc(e);
case IVL_EX_TERNARY:
return translate_ternary(e);
case IVL_EX_CONCAT:
return translate_concat(e);
case IVL_EX_SFUNC:
return translate_sfunc(e);
case IVL_EX_DELAY:
return translate_delay(e);
case IVL_EX_REALNUM:
error("No VHDL translation for real expression at %s:%d",
ivl_expr_file(e), ivl_expr_lineno(e));
return NULL;
default:
error("No VHDL translation for expression at %s:%d (type = %d)",
ivl_expr_file(e), ivl_expr_lineno(e), type);
return NULL;
}
}
/*
* Translate an expression into a time. This is achieved simply
* by multiplying the expression by 1ns.
*/
vhdl_expr *translate_time_expr(ivl_expr_t e)
{
vhdl_expr *time = translate_expr(e);
if (NULL == time)
return NULL;
if (time->get_type()->get_name() != VHDL_TYPE_TIME) {
vhdl_type integer(VHDL_TYPE_INTEGER);
time = time->cast(&integer);
vhdl_expr *ns1 = scale_time(get_active_entity(), 1);
return new vhdl_binop_expr(time, VHDL_BINOP_MULT, ns1,
vhdl_type::time());
}
else // Translating IVL_EX_DELAY will always return a time type
return time;
}
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