elab_lval.cc

/*
 * Copyright (c) 2000-2023 Stephen Williams (steve@icarus.com)
 * Copyright CERN 2012-2013 / Stephen Williams (steve@icarus.com)
 *
 *    This source code is free software; you can redistribute it
 *    and/or modify it in source code form 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 "config.h"

# include  "PExpr.h"
# include  "PPackage.h"
# include  "netlist.h"
# include  "netmisc.h"
# include  "netstruct.h"
# include  "netclass.h"
# include  "netdarray.h"
# include  "netparray.h"
# include  "netvector.h"
# include  "netenum.h"
# include  "compiler.h"
# include  <cstdlib>
# include  <iostream>
# include  <climits>
# include  "ivl_assert.h"

using namespace std;

/*
 * These methods generate a NetAssign_ object for the l-value of the
 * assignment. This is common code for the = and <= statements.
 *
 * What gets generated depends on the structure of the l-value. If the
 * l-value is a simple name (i.e., foo <= <value>) then the NetAssign_
 * is created the width of the foo reg and connected to all the
 * bits.
 *
 * If there is a part select (i.e., foo[3:1] <= <value>) the NetAssign_
 * is made only as wide as it needs to be (3 bits in this example) and
 * connected to the correct bits of foo. A constant bit select is a
 * special case of the part select.
 *
 * If the bit-select is non-constant (i.e., foo[<expr>] = <value>) the
 * NetAssign_ is made wide enough to connect to all the bits of foo,
 * then the mux expression is elaborated and attached to the
 * NetAssign_ node as a b_mux value. The target must interpret the
 * presence of a bmux value as taking a single bit and assigning it to
 * the bit selected by the bmux expression.
 *
 * If the l-value expression is non-trivial, but can be fully
 * evaluated at compile time (meaning any bit selects are constant)
 * then elaboration will make a single NetAssign_ that connects to a
 * synthetic reg that in turn connects to all the proper pins of the
 * l-value.
 *
 * This last case can turn up in statements like: {a, b[1]} = c;
 * rather than create a NetAssign_ for each item in the concatenation,
 * elaboration makes a single NetAssign_ and connects it up properly.
 */


/*
 * The default interpretation of an l-value to a procedural assignment
 * is to try to make a net elaboration, and see if the result is
 * suitable for assignment.
 */
NetAssign_* PExpr::elaborate_lval(Design*, NetScope*, bool, bool, bool) const
{
      cerr << get_fileline() << ": Assignment l-value too complex." << endl;
      return 0;
}

/*
 * Concatenation expressions can appear as l-values. Handle them here.
 *
 * If adjacent l-values in the concatenation are not bit selects, then
 * merge them into a single NetAssign_ object. This can happen is code
 * like ``{ ...a, b, ...}''. As long as "a" and "b" do not have bit
 * selects (or the bit selects are constant) we can merge the
 * NetAssign_ objects.
 *
 * Be careful to get the bit order right. In the expression ``{a, b}''
 * a is the MSB and b the LSB. Connect the LSB to the low pins of the
 * NetAssign_ object.
 */
NetAssign_* PEConcat::elaborate_lval(Design*des,
				     NetScope*scope,
				     bool is_cassign,
				     bool is_force,
				     bool is_init) const
{
      if (repeat_) {
	    cerr << get_fileline() << ": error: Repeat concatenations make "
		  "no sense in l-value expressions. I refuse." << endl;
	    des->errors += 1;
	    return 0;
      }

      NetAssign_*res = 0;

      for (unsigned idx = 0 ;  idx < parms_.size() ;  idx += 1) {

	    if (parms_[idx] == 0) {
		  cerr << get_fileline() << ": error: Empty expressions "
		       << "not allowed in concatenations." << endl;
		  des->errors += 1;
		  continue;
	    }

	    NetAssign_*tmp = parms_[idx]->elaborate_lval(des, scope,
							 is_cassign, is_force, is_init);

	      /* If the l-value doesn't elaborate, the error was
		 already detected and printed. We just skip it and let
		 the compiler catch more errors. */
	    if (tmp == 0) continue;

	    if (tmp->expr_type() == IVL_VT_REAL) {
		  cerr << parms_[idx]->get_fileline() << ": error: "
		       << "concatenation operand can not be real: "
		       << *parms_[idx] << endl;
		  des->errors += 1;
		  continue;
	    }

	      /* A concatenation is always unsigned. */
	    tmp->set_signed(false);

	      /* Link the new l-value to the previous one. */
	    NetAssign_*last = tmp;
	    while (last->more)
		  last = last->more;

	    last->more = res;
	    res = tmp;
      }

      return res;
}


/*
 * Handle the ident as an l-value. This includes bit and part selects
 * of that ident.
 */
NetAssign_* PEIdent::elaborate_lval(Design*des,
				    NetScope*scope,
				    bool is_cassign,
				    bool is_force,
				    bool is_init) const
{

      if (debug_elaborate) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval: "
		 << "Elaborate l-value ident expression: " << *this << endl;
      }

      symbol_search_results sr;
      symbol_search(this, des, scope, path_, &sr);

      NetNet *reg = sr.net;
      pform_name_t &member_path = sr.path_tail;

	/* The l-value must be a variable. If not, then give up and
	   print a useful error message. */
      if (reg == 0) {
	    if (scope->type()==NetScope::FUNC
		&& scope->func_def()->is_void()
		&& scope->basename()==peek_tail_name(path_)) {
		  cerr << get_fileline() << ": error: "
		       << "Cannot assign to " << path_
		       << " because function " << scope_path(scope)
		       << " is void." << endl;
	    } else {
		  cerr << get_fileline() << ": error: Could not find variable ``"
		       << path_ << "'' in ``" << scope_path(scope) <<
			"''" << endl;
	    }
	    des->errors += 1;
	    return 0;
      }

      ivl_assert(*this, reg);

      if (debug_elaborate) {
	    cerr << get_fileline() << ": " << __func__ << ": "
		 << "Found l-value path_=" << path_
		 << " as reg=" << reg->name() << endl;
	    cerr << get_fileline() << ": " << __func__ << ": "
		 << "reg->type()=" << reg->type()
		 << ", reg->unpacked_dimensions()=" << reg->unpacked_dimensions()
		 << endl;
	    if (reg->net_type())
		  cerr << get_fileline() << ": " << __func__ << ": "
		       << "reg->net_type()=" << *reg->net_type() << endl;
	    else
		  cerr << get_fileline() << ": " << __func__ << ": "
		       << "reg->net_type()=<nil>" << endl;
	    const pform_name_t &base_path = sr.path_head;
	    cerr << get_fileline() << ": " << __func__ << ": "
		 << " base_path=" << base_path
		 << ", member_path=" << member_path
		 << endl;
      }

      if (reg->get_const() && !is_init) {
	    cerr << get_fileline() << ": error: Assignment to const signal `"
	         << reg->name() << "` is not allowed." << endl;
	    des->errors++;
	    return nullptr;
      }

      return elaborate_lval_var_(des, scope, is_force, is_cassign, reg,
			         sr.type, member_path);
}

NetAssign_*PEIdent::elaborate_lval_var_(Design *des, NetScope *scope,
				        bool is_force, bool is_cassign,
					NetNet *reg, ivl_type_t data_type,
					pform_name_t tail_path) const
{
	// We are processing the tail of a string of names. For
	// example, the Verilog may be "a.b.c", so we are processing
	// "c" at this point.
      const name_component_t&name_tail = path_.back();

	// Use the last index to determine what kind of select
	// (bit/part/etc) we are processing. For example, the Verilog
	// may be "a.b.c[1][2][<index>]". All but the last index must
	// be simple expressions, only the <index> may be a part
	// select etc., so look at it to determine how we will be
	// proceeding.
      index_component_t::ctype_t use_sel = index_component_t::SEL_NONE;
      if (!name_tail.index.empty())
	    use_sel = name_tail.index.back().sel;

	// Special case: The l-value is an entire memory, or array
	// slice. Detect the situation by noting if the index count
	// is less than the array dimensions (unpacked).
      if (reg->unpacked_dimensions() > name_tail.index.size()) {
	    if (gn_system_verilog()) {
		  if (name_tail.index.empty()) {
			NetAssign_*lv = new NetAssign_(reg);
			return lv;
		  }
		  cerr << get_fileline() << ": sorry: Assignment to an "
		        " array slice is not yet supported."
		       << endl;
	    } else {
		  cerr << get_fileline() << ": error: Assignment to an entire"
		        " array or to an array slice requires SystemVerilog."
		       << endl;
	    }
	    des->errors += 1;
	    return 0;
      }

	/* Get the signal referenced by the identifier, and make sure
	   it is a register. Wires are not allowed in this context,
	   unless this is the l-value of a force. */
      if ((reg->type() != NetNet::REG)
	  && (reg->type() != NetNet::UNRESOLVED_WIRE)
	  && !is_force) {
	    cerr << get_fileline() << ": error: " << path_ <<
		  " is not a valid l-value in " << scope_path(scope) <<
		  "." << endl;
	    cerr << reg->get_fileline() << ":      : " << path_ <<
		  " is declared here as " << reg->type() << "." << endl;
	    des->errors += 1;
	    return 0;
      }


	// If we find that the matched variable is a packed struct,
	// then we can handled it with the net_packed_member_ method.
      if (reg->struct_type() && !tail_path.empty()) {
	    NetAssign_*lv = new NetAssign_(reg);
	    elaborate_lval_net_packed_member_(des, scope, lv, tail_path);
	    return lv;
      }

	// If the variable is a class object, then handle it with the
	// net_class_member_ method.
      const netclass_t *class_type = dynamic_cast<const netclass_t *>(data_type);
      if (class_type && !tail_path.empty() && gn_system_verilog())
	    return elaborate_lval_net_class_member_(des, scope, class_type, reg, tail_path);


	// Past this point, we should have taken care of the cases
	// where the name is a member/method of a struct/class.
	// XXXX ivl_assert(*this, method_name.nil());
      ivl_assert(*this, tail_path.empty());

      bool need_const_idx = is_cassign || is_force || (reg->type()==NetNet::UNRESOLVED_WIRE);

      if (reg->unpacked_dimensions() > 0)
	    return elaborate_lval_net_word_(des, scope, reg, need_const_idx);

	// This must be after the array word elaboration above!
      if (reg->get_scalar() &&
          use_sel != index_component_t::SEL_NONE) {
	    cerr << get_fileline() << ": error: can not select part of ";
	    if (reg->data_type() == IVL_VT_REAL) cerr << "real: ";
	    else cerr << "scalar: ";
	    cerr << reg->name() << endl;
	    des->errors += 1;
	    return 0;
      }

      if (use_sel == index_component_t::SEL_PART) {
	    NetAssign_*lv = new NetAssign_(reg);
	    elaborate_lval_net_part_(des, scope, lv);
	    return lv;
      }

      if (use_sel == index_component_t::SEL_IDX_UP ||
          use_sel == index_component_t::SEL_IDX_DO) {
	    NetAssign_*lv = new NetAssign_(reg);
	    elaborate_lval_net_idx_(des, scope, lv, use_sel, need_const_idx);
	    return lv;
      }


      if (use_sel == index_component_t::SEL_BIT) {
	    if (reg->darray_type()) {
		  NetAssign_*lv = new NetAssign_(reg);
		  elaborate_lval_darray_bit_(des, scope, lv);
		  return lv;
	    } else {
		  NetAssign_*lv = new NetAssign_(reg);
		  elaborate_lval_net_bit_(des, scope, lv, need_const_idx);
		  return lv;
	    }
      }

      ivl_assert(*this, use_sel == index_component_t::SEL_NONE);

      if (reg->type()==NetNet::UNRESOLVED_WIRE && !is_force) {
	    cerr << get_fileline() << ": error: "
		 << path_ << " Unable to assign to unresolved wires."
		 << endl;
	    des->errors += 1;
	    return 0;
      }

	/* No select expressions. */

      NetAssign_*lv = new NetAssign_(reg);
      lv->set_signed(reg->get_signed());

      return lv;
}

NetAssign_* PEIdent::elaborate_lval_net_word_(Design*des,
					      NetScope*scope,
					      NetNet*reg,
					      bool need_const_idx) const
{
      const name_component_t&name_tail = path_.back();
      ivl_assert(*this, !name_tail.index.empty());

      if (debug_elaborate) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval_net_word_: "
		 << "Handle as n-dimensional array." << endl;
      }

      if (name_tail.index.size() < reg->unpacked_dimensions()) {
	    cerr << get_fileline() << ": error: Array " << reg->name()
		 << " needs " << reg->unpacked_dimensions() << " indices,"
		 << " but got only " << name_tail.index.size() << "." << endl;
	    des->errors += 1;
	    return 0;
      }

	// Make sure there are enough indices to address an array element.
      const index_component_t&index_head = name_tail.index.front();
      if (index_head.sel == index_component_t::SEL_PART) {
	    cerr << get_fileline() << ": error: cannot perform a part "
	         << "select on array " << reg->name() << "." << endl;
	    des->errors += 1;
	    return 0;
      }


	// Evaluate all the index expressions into an
	// "unpacked_indices" array.
      list<NetExpr*>unpacked_indices;
      list<long> unpacked_indices_const;
      indices_flags flags;
      indices_to_expressions(des, scope, this,
			     name_tail.index, reg->unpacked_dimensions(),
			     false,
			     flags,
			     unpacked_indices,
			     unpacked_indices_const);

      NetExpr*canon_index = 0;
      if (flags.invalid) {
	    // Nothing to do.

      } else if (flags.undefined) {
	    cerr << get_fileline() << ": warning: "
		 << "ignoring undefined l-value array access "
		 << reg->name() << as_indices(unpacked_indices)
		 << "." << endl;

      } else if (flags.variable) {
	    if (need_const_idx) {
		  cerr << get_fileline() << ": error: array '" << reg->name()
		       << "' index must be a constant in this context." << endl;
		  des->errors += 1;
		  return 0;
	    }
	    ivl_assert(*this, unpacked_indices.size() == reg->unpacked_dimensions());
	    canon_index = normalize_variable_unpacked(reg, unpacked_indices);

      } else {
	    ivl_assert(*this, unpacked_indices_const.size() == reg->unpacked_dimensions());
	    canon_index = normalize_variable_unpacked(reg, unpacked_indices_const);

	    if (canon_index == 0) {
		  cerr << get_fileline() << ": warning: "
		       << "ignoring out of bounds l-value array access "
		       << reg->name() << as_indices(unpacked_indices_const)
		       << "." << endl;
	    }
      }

	// Ensure invalid array accesses are ignored.
      if (canon_index == 0)
	    canon_index = new NetEConst(verinum(verinum::Vx));
      canon_index->set_line(*this);

      if (debug_elaborate) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval_net_word_: "
		 << "canon_index=" << *canon_index << endl;
      }

      if (reg->type()==NetNet::UNRESOLVED_WIRE) {
	    cerr << get_fileline() << ": error: "
		 << "Unable to assign words of unresolved wire array." << endl;
	    des->errors += 1;
	    return 0;
      }

      NetAssign_*lv = new NetAssign_(reg);
      lv->set_word(canon_index);

      if (debug_elaborate)
	    cerr << get_fileline() << ": debug: Set array word=" << *canon_index << endl;


	/* An array word may also have part selects applied to them. */

      index_component_t::ctype_t use_sel = index_component_t::SEL_NONE;
      if (name_tail.index.size() > reg->unpacked_dimensions())
	    use_sel = name_tail.index.back().sel;

      if (reg->get_scalar() &&
          use_sel != index_component_t::SEL_NONE) {
	    cerr << get_fileline() << ": error: can not select part of ";
	    if (reg->data_type() == IVL_VT_REAL) cerr << "real";
	    else cerr << "scalar";
	    cerr << " array word: " << reg->name()
	         << as_indices(unpacked_indices) << endl;
	    des->errors += 1;
	    return 0;
      }

      if (use_sel == index_component_t::SEL_BIT)
	    elaborate_lval_net_bit_(des, scope, lv, need_const_idx);

      if (use_sel == index_component_t::SEL_PART)
	    elaborate_lval_net_part_(des, scope, lv);

      if (use_sel == index_component_t::SEL_IDX_UP ||
          use_sel == index_component_t::SEL_IDX_DO)
	    elaborate_lval_net_idx_(des, scope, lv, use_sel, need_const_idx);

      return lv;
}

bool PEIdent::elaborate_lval_net_bit_(Design*des,
				      NetScope*scope,
				      NetAssign_*lv,
				      bool need_const_idx) const
{
      list<long>prefix_indices;
      bool rc = calculate_packed_indices_(des, scope, lv->sig(), prefix_indices);
      if (!rc) return false;

      const name_component_t&name_tail = path_.back();
      ivl_assert(*this, !name_tail.index.empty());

      const index_component_t&index_tail = name_tail.index.back();
      ivl_assert(*this, index_tail.msb != 0);
      ivl_assert(*this, index_tail.lsb == 0);

      NetNet*reg = lv->sig();
      ivl_assert(*this, reg);

	// Bit selects have a single select expression. Evaluate the
	// constant value and treat it as a part select with a bit
	// width of 1.
      NetExpr*mux = elab_and_eval(des, scope, index_tail.msb, -1);
      long lsb = 0;

      if (mux && mux->expr_type() == IVL_VT_REAL) {
           cerr << get_fileline() << ": error: Index expression for "
                << reg->name() << "[" << *mux
                << "] cannot be a real value." << endl;
           des->errors += 1;
           return false;
      }

      if (NetEConst*index_con = dynamic_cast<NetEConst*> (mux)) {
	      // The index has a constant defined value.
	    if (index_con->value().is_defined()) {
		  lsb = index_con->value().as_long();
		  mux = 0;
	      // The index is undefined and this is a packed array.
	    } else if (prefix_indices.size()+2 <= reg->packed_dims().size()) {
		  long loff;
		  unsigned long lwid;
		  bool rcl = reg->sb_to_slice(prefix_indices, lsb, loff, lwid);
		  ivl_assert(*this, rcl);
		  if (warn_ob_select) {
			cerr << get_fileline()
			     << ": warning: L-value packed array select of "
			     << reg->name();
			if (reg->unpacked_dimensions() > 0) cerr << "[]";
			cerr << " has an undefined index." << endl;
		  }
		  lv->set_part(new NetEConst(verinum(verinum::Vx)), lwid);
		  return true;
	      // The index is undefined and this is a bit select.
	    } else {
		  if (warn_ob_select) {
			cerr << get_fileline()
			     << ": warning: L-value bit select of "
			     << reg->name();
			if (reg->unpacked_dimensions() > 0) cerr << "[]";
			cerr << " has an undefined index." << endl;
		  }
		  lv->set_part(new NetEConst(verinum(verinum::Vx)), 1);
		  return true;
	    }
      }

      if (debug_elaborate && (reg->type()==NetNet::UNRESOLVED_WIRE)) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval_net_bit_: "
		 << "Try to assign bits of unresolved wire."
		 << endl;
      }

	// Notice that we might be assigning to an unresolved wire. This
	// can happen if we are actually assigning to a variable that
	// has a partial continuous assignment to it. If that is the
	// case, then the bit select must be constant.
      ivl_assert(*this, need_const_idx || (reg->type()!=NetNet::UNRESOLVED_WIRE));


      if (prefix_indices.size()+2 <= reg->packed_dims().size()) {
	      // Special case: this is a slice of a multi-dimensional
	      // packed array. For example:
	      //   reg [3:0][7:0] x;
	      //   x[2] = ...
	      // This shows up as the prefix_indices being too short
	      // for the packed dimensions of the vector. What we do
	      // here is convert to a "slice" of the vector.
	    if (mux == 0) {
		  long loff;
		  unsigned long lwid;
		  bool rcl = reg->sb_to_slice(prefix_indices, lsb, loff, lwid);
		  ivl_assert(*this, rcl);

		  if (reg->type()==NetNet::UNRESOLVED_WIRE) {
			bool rct = reg->test_and_set_part_driver(loff+lwid-1, loff);
			if (rct) {
			      cerr << get_fileline() << ": error: "
				   << "These bits are already driven." << endl;
			      des->errors += 1;
			}
		  }

		  lv->set_part(new NetEConst(verinum(loff)), lwid);

	    } else {
		  ivl_assert(*this, reg->type()!=NetNet::UNRESOLVED_WIRE);
		  unsigned long lwid;
		  mux = normalize_variable_slice_base(prefix_indices, mux,
						      reg, lwid);
		  lv->set_part(mux, lwid);
	    }

      } else if (reg->data_type() == IVL_VT_STRING) {
	    ivl_assert(*this, reg->type()!=NetNet::UNRESOLVED_WIRE);
	      // Special case: This is a select of a string
	      // variable. The target of the assignment is a character
	      // select of a string. Force the r-value to be an 8bit
	      // vector and set the "part" to be the character select
	      // expression. The code generator knows what to do with
	      // this.
	    if (debug_elaborate) {
		  cerr << get_fileline() << ": debug: "
		       << "Bit select of string becomes character select." << endl;
	    }
	    if (!mux)
		  mux = new NetEConst(verinum(lsb));
	    lv->set_part(mux, &netvector_t::atom2s8);

      } else if (mux) {
	    ivl_assert(*this, reg->type()!=NetNet::UNRESOLVED_WIRE);

	      // Non-constant bit mux. Correct the mux for the range
	      // of the vector, then set the l-value part select
	      // expression.
	    if (need_const_idx) {
		  cerr << get_fileline() << ": error: '" << reg->name()
		       << "' bit select must be a constant in this context."
		       << endl;
		  des->errors += 1;
		  return false;
	    }
	    mux = normalize_variable_bit_base(prefix_indices, mux, reg);
	    lv->set_part(mux, 1);

      } else if (reg->vector_width() == 1 && reg->sb_is_valid(prefix_indices,lsb)) {
	      // Constant bit mux that happens to select the only bit
	      // of the l-value. Don't bother with any select at all.

	      // NOTE: Don't know what to do about unresolved wires
	      // here, but they are probably wrong.
	    ivl_assert(*this, reg->type()!=NetNet::UNRESOLVED_WIRE);

      } else {
	      // Constant bit select that does something useful.
	    long loff = reg->sb_to_idx(prefix_indices,lsb);

	    if (warn_ob_select && (loff < 0 || loff >= (long)reg->vector_width())) {
		  cerr << get_fileline() << ": warning: bit select "
		       << reg->name() << "[" <<lsb<<"]"
		       << " is out of range." << endl;
	    }

	    if (reg->type()==NetNet::UNRESOLVED_WIRE) {
		  bool rct = reg->test_and_set_part_driver(loff, loff);
		  if (rct) {
			cerr << get_fileline() << ": error: "
			     << "Bit " << loff << " is already driven." << endl;
			des->errors += 1;
		  }
	    }

	    lv->set_part(new NetEConst(verinum(loff)), 1);
      }

      return true;
}

bool PEIdent::elaborate_lval_darray_bit_(Design*des, NetScope*scope, NetAssign_*lv)const
{
      const name_component_t&name_tail = path_.back();
      ivl_assert(*this, !name_tail.index.empty());

	// For now, only support single-dimension dynamic arrays.
      ivl_assert(*this, name_tail.index.size() == 1);

      if (lv->sig()->type()==NetNet::UNRESOLVED_WIRE) {
	    cerr << get_fileline() << ": error: "
		 << path_ << " Unable to darray word select unresolved wires."
		 << endl;
	    des->errors += 1;
	    return false;
      }

      const index_component_t&index_tail = name_tail.index.back();
      ivl_assert(*this, index_tail.msb != 0);
      ivl_assert(*this, index_tail.lsb == 0);

	// Evaluate the select expression...
      NetExpr*mux = elab_and_eval(des, scope, index_tail.msb, -1);

      lv->set_word(mux);

      return true;
}

bool PEIdent::elaborate_lval_net_part_(Design*des,
				       NetScope*scope,
				       NetAssign_*lv) const
{
      if (lv->sig()->data_type() == IVL_VT_STRING) {
           cerr << get_fileline() << ": error: Cannot part select assign to a string ('"
                << lv->sig()->name() << "')." << endl;
           des->errors += 1;
           return false;
      }

      list<long> prefix_indices;
      bool rc = calculate_packed_indices_(des, scope, lv->sig(), prefix_indices);
      ivl_assert(*this, rc);

	// The range expressions of a part select must be
	// constant. The calculate_parts_ function calculates the
	// values into msb and lsb.
      long msb, lsb;
      bool parts_defined_flag;
      bool flag = calculate_parts_(des, scope, msb, lsb, parts_defined_flag);
      if (!flag) return false;

      NetNet*reg = lv->sig();
      ivl_assert(*this, reg);

      if (! parts_defined_flag) {
	    if (warn_ob_select) {
		  cerr << get_fileline()
		       << ": warning: L-value part select of "
		       << reg->name();
		  if (reg->unpacked_dimensions() > 0) cerr << "[]";
		  cerr << " has an undefined index." << endl;
	    }
	      // Use a width of two here so we can distinguish between an
	      // undefined bit or part select.
	    lv->set_part(new NetEConst(verinum(verinum::Vx)), 2);
	    return true;
      }

      if (reg->type()==NetNet::UNRESOLVED_WIRE) {
	    bool rct = reg->test_and_set_part_driver(msb, lsb);
	    if (rct) {
		  cerr << get_fileline() << ": error: "
		       << path_ << "Part select is double-driving unresolved wire."
		       << endl;
		  des->errors += 1;
		  return false;
	    }
      }

      const netranges_t&packed = reg->packed_dims();

      long loff, moff;
      long wid;
      if (prefix_indices.size()+1 < packed.size()) {
	      // If there are fewer indices then there are packed
	      // dimensions, then this is a range of slices. Calculate
	      // it into a big slice.
	    bool lrc, mrc;
	    unsigned long tmp_lwid, tmp_mwid;
	    lrc = reg->sb_to_slice(prefix_indices, lsb, loff, tmp_lwid);
	    mrc = reg->sb_to_slice(prefix_indices, msb, moff, tmp_mwid);
	    if (!mrc || !lrc) {
		  cerr << get_fileline() << ": error: ";
		  cerr << "Part-select [" << msb << ":" << lsb;
		  cerr << "] exceeds the declared bounds for ";
		  cerr << reg->name();
		  if (reg->unpacked_dimensions() > 0) cerr << "[]";
		  cerr << "." << endl;
		  des->errors += 1;
		  return 0;
	    }

	    if (loff < moff) {
		  moff = moff + tmp_mwid - 1;
	    } else {
		  long ltmp = moff;
		  moff = loff + tmp_lwid - 1;
		  loff = ltmp;
	    }
	    wid = moff - loff + 1;

      } else {
	    loff = reg->sb_to_idx(prefix_indices,lsb);
	    moff = reg->sb_to_idx(prefix_indices,msb);
	    wid = moff - loff + 1;

	    if (moff < loff) {
		  cerr << get_fileline() << ": error: part select "
		       << reg->name() << "[" << msb<<":"<<lsb<<"]"
		       << " is reversed." << endl;
		  des->errors += 1;
		  return false;
	    }
      }

	// Special case: The range winds up selecting the entire
	// vector. Treat this as no part select at all.
      if (loff == 0 && moff == (long)(reg->vector_width()-1)) {
	    return true;
      }

	/* If the part select extends beyond the extremes of the
	   variable, then output a warning. Note that loff is
	   converted to normalized form so is relative the
	   variable pins. */

      if (warn_ob_select && (loff < 0 || moff >= (long)reg->vector_width())) {
	    cerr << get_fileline() << ": warning: Part select "
		 << reg->name() << "[" << msb<<":"<<lsb<<"]"
		 << " is out of range." << endl;
      }

      lv->set_part(new NetEConst(verinum(loff)), wid);

      return true;
}

bool PEIdent::elaborate_lval_net_idx_(Design*des,
				      NetScope*scope,
				      NetAssign_*lv,
				      index_component_t::ctype_t use_sel,
				      bool need_const_idx) const
{
      if (lv->sig()->data_type() == IVL_VT_STRING) {
           cerr << get_fileline() << ": error: Cannot index part select assign to a string ('"
                << lv->sig()->name() << "')." << endl;
           des->errors += 1;
           return false;
      }

      list<long>prefix_indices;
      bool rc = calculate_packed_indices_(des, scope, lv->sig(), prefix_indices);
      ivl_assert(*this, rc);

      const name_component_t&name_tail = path_.back();;
      ivl_assert(*this, !name_tail.index.empty());

      const index_component_t&index_tail = name_tail.index.back();
      ivl_assert(*this, index_tail.msb != 0);
      ivl_assert(*this, index_tail.lsb != 0);

      NetNet*reg = lv->sig();
      ivl_assert(*this, reg);

      unsigned long wid;
      calculate_up_do_width_(des, scope, wid);

      NetExpr*base = elab_and_eval(des, scope, index_tail.msb, -1);

      if (base && base->expr_type() == IVL_VT_REAL) {
	    cerr << get_fileline() << ": error: Indexed part select base "
	            "expression for ";
	    cerr << lv->sig()->name() << "[" << *base;
	    if (index_tail.sel == index_component_t::SEL_IDX_UP) {
		  cerr << "+:";
	    } else {
		  cerr << "-:";
	    }
	    cerr << wid << "] cannot be a real value." << endl;
	    des->errors += 1;
	    return 0;
      }

      ivl_select_type_t sel_type = IVL_SEL_OTHER;

	// Handle the special case that the base is constant. For this
	// case we can reduce the expression.
      if (NetEConst*base_c = dynamic_cast<NetEConst*> (base)) {
	      // For the undefined case just let the constant pass and
	      // we will handle it in the code generator.
	    if (base_c->value().is_defined()) {
		  long lsv = base_c->value().as_long();
		  long rel_base = 0;
		    // Get the signal range.
		  const netranges_t&packed = reg->packed_dims();
		  if (prefix_indices.size()+1 < reg->packed_dims().size()) {
			  // Here we are selecting one or more sub-arrays.
			  // Make this work by finding the indexed sub-arrays and
			  // creating a generated slice that spans the whole range.
			long loff, moff;
			unsigned long lwid, mwid;
			bool lrc, mrc;
			mrc = reg->sb_to_slice(prefix_indices, lsv, moff, mwid);
			if (use_sel == index_component_t::SEL_IDX_UP)
			      lrc = reg->sb_to_slice(prefix_indices, lsv+wid-1, loff, lwid);
			else
			      lrc = reg->sb_to_slice(prefix_indices, lsv-wid+1, loff, lwid);
			if (!mrc || !lrc) {
			      cerr << get_fileline() << ": error: ";
			      cerr << "Part-select [" << lsv;
			      if (index_tail.sel == index_component_t::SEL_IDX_UP) {
				    cerr << "+:";
			      } else {
				    cerr << "-:";
			      }
			      cerr << wid << "] exceeds the declared bounds for ";
			      cerr << reg->name();
			      if (reg->unpacked_dimensions() > 0) cerr << "[]";
			      cerr << "." << endl;
			      des->errors += 1;
			      return 0;
			}
			ivl_assert(*this, lwid == mwid);

			if (moff > loff) {
			      rel_base = loff;
			      wid = moff + mwid - loff;
			} else {
			      rel_base = moff;
			      wid = loff + lwid - moff;
			}
		  } else {
			long offset = 0;
			  // We want the last range, which is where we work.
			const netrange_t&rng = packed.back();
			if (((rng.get_msb() < rng.get_lsb()) &&
			     use_sel == index_component_t::SEL_IDX_UP) ||
			    ((rng.get_msb() > rng.get_lsb()) &&
			     use_sel == index_component_t::SEL_IDX_DO)) {
			      offset = -wid + 1;
			}
			rel_base = reg->sb_to_idx(prefix_indices,lsv) + offset;
		  }
		  delete base;
		    /* If we cover the entire lvalue just skip the select. */
		  if (rel_base == 0 && wid == reg->vector_width()) return true;
		  base = new NetEConst(verinum(rel_base));
		  if (warn_ob_select) {
			if (rel_base < 0) {
			      cerr << get_fileline() << ": warning: " << reg->name();
			      if (reg->unpacked_dimensions() > 0) cerr << "[]";
			      cerr << "[" << lsv;
			      if (use_sel == index_component_t::SEL_IDX_UP) {
				    cerr << "+:";
			      } else {
				    cerr << "-:";
			      }
			      cerr << wid << "] is selecting before vector." << endl;
			}
			if (rel_base + wid > reg->vector_width()) {
			      cerr << get_fileline() << ": warning: " << reg->name();
			      if (reg->unpacked_dimensions() > 0) cerr << "[]";
			      cerr << "[" << lsv;
			      if (use_sel == index_component_t::SEL_IDX_UP) {
				    cerr << "+:";
			      } else {
				    cerr << "-:";
			      }
			      cerr << wid << "] is selecting after vector." << endl;
			}
		  }
	    } else if (warn_ob_select) {
		  cerr << get_fileline() << ": warning: L-value indexed part "
		       << "select of " << reg->name();
		  if (reg->unpacked_dimensions() > 0) cerr << "[]";
		  cerr << " has an undefined base." << endl;
	    }
      } else {
	    if (need_const_idx) {
		  cerr << get_fileline() << ": error: '" << reg->name()
		       << "' base index must be a constant in this context."
		       << endl;
		  des->errors += 1;
		  return false;
	    }
	    ivl_assert(*this, prefix_indices.size()+1 == reg->packed_dims().size());
	      /* Correct the mux for the range of the vector. */
	    if (use_sel == index_component_t::SEL_IDX_UP) {
		  base = normalize_variable_part_base(prefix_indices, base,
						      reg, wid, true);
		  sel_type = IVL_SEL_IDX_UP;
	    } else {
		    // This is assumed to be a SEL_IDX_DO.
		  base = normalize_variable_part_base(prefix_indices, base,
						      reg, wid, false);
		  sel_type = IVL_SEL_IDX_DOWN;
	    }
      }

      if (debug_elaborate)
	    cerr << get_fileline() << ": debug: Set part select width="
		 << wid << ", base=" << *base << endl;

      lv->set_part(base, wid, sel_type);

      return true;
}

/*
 * When the l-value turns out to be a class object, this method is
 * called with the bound variable, and the method path. For example,
 * if path_=a.b.c and a.b binds to the variable, then sig is b, and
 * member_path=c. if path_=obj.base.x, and base_path=obj, then sig is
 * obj, and member_path=base.x.
 */
NetAssign_* PEIdent::elaborate_lval_net_class_member_(Design*des, NetScope*scope,
				    const netclass_t *class_type, NetNet*sig,
				    pform_name_t member_path) const
{
      if (debug_elaborate) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval_net_class_member_: "
		 << "l-value is property " << member_path
		 << " of " << sig->name() << "." << endl;
      }

      ivl_assert(*this, class_type);

	// Iterate over the member_path. This handles nested class
	// object, by generating nested NetAssign_ object. We start
	// with lv==0, so the front of the member_path is the member
	// of the outermost class. This generates an lv from sig. Then
	// iterate over the remaining of the member_path, replacing
	// the outer lv with an lv that nests the lv from the previous
	// iteration.
      NetAssign_*lv = 0;
      do {
	      // Start with the first component of the member path...
	    perm_string method_name = peek_head_name(member_path);
	      // Pull that component from the member_path. We need to
	      // know the current member being worked on, and will
	      // need to know if there are more members to be worked on.
	    name_component_t member_cur = member_path.front();
	    member_path.pop_front();

	    if (debug_elaborate) {
		  cerr << get_fileline() << ": PEIdent::elaborate_lval_net_class_member_: "
		       << "Processing member_cur=" << member_cur
		       << endl;
	    }

	      // Make sure the property is really present in the class. If
	      // not, then generate an error message and return an error.
	    int pidx = class_type->property_idx_from_name(method_name);
	    if (pidx < 0) {
		  cerr << get_fileline() << ": error: Class " << class_type->get_name()
		       << " does not have a property " << method_name << "." << endl;
		  des->errors += 1;
		  return 0;
	    }

	    property_qualifier_t qual = class_type->get_prop_qual(pidx);
	    if (qual.test_local() && ! class_type->test_scope_is_method(scope)) {
		  cerr << get_fileline() << ": error: "
		       << "Local property " << class_type->get_prop_name(pidx)
		       << " is not accessible (l-value) in this context."
		       << " (scope=" << scope_path(scope) << ")" << endl;
		  des->errors += 1;

	    } else if (qual.test_static()) {

		    // Special case: this is a static property. Ignore the
		    // "this" sig and use the property itself, which is not
		    // part of the sig, as the l-value.
		  NetNet*psig = class_type->find_static_property(method_name);
		  ivl_assert(*this, psig);

		  lv = new NetAssign_(psig);
		  return lv;

	    } else if (qual.test_const()) {
		 if (class_type->get_prop_initialized(pidx)) {
		       cerr << get_fileline() << ": error: "
			    << "Property " << class_type->get_prop_name(pidx)
			    << " is constant in this method."
			    << " (scope=" << scope_path(scope) << ")" << endl;
		       des->errors++;
		 } else if (scope->basename() != "new" && scope->basename() != "new@") {
		       cerr << get_fileline() << ": error: "
			    << "Property " << class_type->get_prop_name(pidx)
			    << " is constant in this method."
			    << " (scope=" << scope_path(scope) << ")" << endl;
		       des->errors++;
		 } else {
			 // Mark this property as initialized. This is used
			 // to know that we have initialized the constant
			 // object so the next assignment will be marked as
			 // illegal.
		       class_type->set_prop_initialized(pidx);

		       if (debug_elaborate) {
			     cerr << get_fileline() << ": PEIdent::elaborate_lval_method_class_member_: "
				  << "Found initializers for property " << class_type->get_prop_name(pidx) << endl;
		       }
		 }
	    }

	    lv = lv? new NetAssign_(lv) : new NetAssign_(sig);
	    lv->set_property(method_name, pidx);

	      // Now get the type of the property.
	    ivl_type_t ptype = class_type->get_prop_type(pidx);
	    const netdarray_t*mtype = dynamic_cast<const netdarray_t*> (ptype);
	    if (mtype) {
		  if (! member_cur.index.empty()) {
			cerr << get_fileline() << ": sorry: "
			     << "Array index of array properties not supported."
			     << endl;
			des->errors += 1;
		  }
	    }
	    NetExpr *canon_index = nullptr;
	    if (!member_cur.index.empty()) {
		  if (const netsarray_t *stype = dynamic_cast<const netsarray_t*>(ptype)) {
			canon_index = make_canonical_index(des, scope, this,
							   member_cur.index, stype, false);

		  } else {
			cerr << get_fileline() << ": error: "
			     << "Index expressions don't apply to this type of property." << endl;
			des->errors++;
		  }
	    }

	    if (const netuarray_t *tmp_ua = dynamic_cast<const netuarray_t*>(ptype)) {
		  const auto &dims = tmp_ua->static_dimensions();

		  if (debug_elaborate) {
			cerr << get_fileline() << ": PEIdent::elaborate_lval_method_class_member_: "
			     << "Property " << class_type->get_prop_name(pidx)
			     << " has " << dims.size() << " dimensions, "
			     << " got " << member_cur.index.size() << " indices." << endl;
			if (canon_index) {
			      cerr << get_fileline() << ": PEIdent::elaborate_lval_method_class_member_: "
				   << "Canonical index is:" << *canon_index << endl;
			}
		  }

		  if (dims.size() != member_cur.index.size()) {
			cerr << get_fileline() << ": error: "
			     << "Got " << member_cur.index.size() << " indices, "
			     << "expecting " << dims.size()
			     << " to index the property " << class_type->get_prop_name(pidx) << "." << endl;
			des->errors++;
		  }
	    }

	    if (canon_index)
		  lv->set_word(canon_index);

	      // If the current member is a class object, then get the
	      // type. We may wind up iterating, and need the proper
	      // class type.
	    class_type = dynamic_cast<const netclass_t*>(ptype);

      } while (!member_path.empty());


      return lv;
}

/*
 * This method is caled to handle l-value identifiers that are packed
 * structs. The lv is already attached to the variable, so this method
 * calculates the part select that is defined by the member_path. For
 * example, if the path_ is main.sub.sub_local, and the variable is
 * main, then we know at this point that main is a packed struct, and
 * lv contains the reference to the bound variable (main). In this
 * case member_path==sub.sub_local, and it is up to this method to
 * work out the part select that the member_path represents.
 */
bool PEIdent::elaborate_lval_net_packed_member_(Design*des, NetScope*scope,
						NetAssign_*lv,
						pform_name_t member_path) const
{
      if (debug_elaborate) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
		 << "path_=" << path_
		 << " member_path=" << member_path
		 << endl;
      }

      NetNet*reg = lv->sig();
      ivl_assert(*this, reg);

      const netstruct_t*struct_type = reg->struct_type();
      ivl_assert(*this, struct_type);
      if (debug_elaborate) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
		 << "Type=" << *struct_type
		 << endl;
      }

      if (! struct_type->packed()) {
	    cerr << get_fileline() << ": sorry: Only packed structures "
		 << "are supported in l-value." << endl;
	    des->errors += 1;
	    return false;
      }

	// Looking for the base name. We need that to know about
	// indices we may need to apply. This is to handle the case
	// that the base is an array of structs, and not just a
	// struct.
      pform_name_t::const_reverse_iterator name_idx = path_.name.rbegin();
      for (size_t idx = 1 ; idx < member_path.size() ; idx += 1)
	    ++ name_idx;
      if (name_idx->name != peek_head_name(member_path)) {
	    cerr << get_fileline() << ": internal error: "
		 << "name_idx=" << name_idx->name
		 << ", expecting member_name=" << peek_head_name(member_path)
		 << endl;
	    des->errors += 1;
	    return false;
      }
      ivl_assert(*this, name_idx->name == peek_head_name(member_path));
      ++ name_idx;
      const name_component_t&name_base = *name_idx;

	// Shouldn't be seeing unpacked arrays of packed structs...
      ivl_assert(*this, reg->unpacked_dimensions() == 0);

	// These make up the "part" select that is the equivilent of
	// following the member path through the nested structs. To
	// start with, the off[set] is zero, and use_width is the
	// width of the entire variable. The first member_comp is at
	// some offset within the variable, and will have a reduced
	// width. As we step through the member_path the off
	// increases, and use_width shrinks.
      unsigned long off = 0;
      unsigned long use_width = struct_type->packed_width();
      ivl_type_t member_type;

      pform_name_t completed_path;
      do {
	    const name_component_t member_comp = member_path.front();
	    const perm_string&member_name = member_comp.name;

	    if (debug_elaborate) {
		  cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
		       << "Processing member_comp=" << member_comp
		       << " (completed_path=" << completed_path << ")"
		       << endl;
	    }

	      // This is a packed member, so the name is of the form
	      // "a.b[...].c[...]" which means that the path_ must have at
	      // least 2 components. We are processing "c[...]" at that
	      // point (otherwise known as member_name) and we have a
	      // reference to it in member_comp.

	      // The member_path is the members we want to follow for the
	      // variable. For example, main[N].a.b may have main[N] as the
	      // base_name, and member_path=a.b. The member_name is the
	      // start of the member_path, and is "a". The member_name
	      // should be a member of the struct_type type.

	      // Calculate the offset within the packed structure of the
	      // member, and any indices. We will add in the offset of the
	      // struct into the packed array later. Note that this works
	      // for packed unions as well (although the offset will be 0
	      // for union members).
	    unsigned long tmp_off;
	    const netstruct_t::member_t* member = struct_type->packed_member(member_name, tmp_off);

	    if (member == 0) {
		  cerr << get_fileline() << ": error: Member " << member_name
		       << " is not a member of struct type of "
		       << reg->name()
		       << "." << completed_path << endl;
		  des->errors += 1;
		  return false;
	    }
	    if (debug_elaborate) {
		  cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
		       << "Member type: " << *(member->net_type)
		       << endl;
	    }

	    off += tmp_off;
	    ivl_assert(*this, use_width >= (unsigned long)member->net_type->packed_width());
	    use_width = member->net_type->packed_width();

	      // At this point, off and use_width are the part select
	      // expressed by the member_comp, which is a member of the
	      // struct. We can further refine the part select with any
	      // indices that might be present.

	      // Get the index component type. At this point, we only
	      // support bit select or none.
	    index_component_t::ctype_t use_sel = index_component_t::SEL_NONE;
	    if (!member_comp.index.empty())
		  use_sel = member_comp.index.back().sel;

	    if (use_sel != index_component_t::SEL_NONE
		&& use_sel != index_component_t::SEL_BIT
		&& use_sel != index_component_t::SEL_PART) {
		  cerr << get_fileline() << ": sorry: Assignments to part selects of "
			"a struct member are not yet supported." << endl;
		  des->errors += 1;
		  return false;
	    }

	    member_type = member->net_type;

	    if (const netvector_t*mem_vec = dynamic_cast<const netvector_t*>(member->net_type)) {
		    // If the member type is a netvector_t, then it is a
		    // vector of atom or scaler objects. For example, if the
		    // l-value expression is "foo.member[1][2]",
		    // then the member should be something like:
		    //    ... logic [h:l][m:n] member;
		    // There should be index expressions index the vector
		    // down, but there doesn't need to be all of them. We
		    // can, for example, be selecting a part of the vector.

		    // We only need to process this if there are any
		    // index expressions. If not, then the packed
		    // vector can be handled atomically.

		    // In any case, this should be the tail of the
		    // member_path, because the array element of this
		    // kind of array cannot be a struct.
		  if (!member_comp.index.empty()) {
			  // These are the dimensions defined by the type
			const netranges_t&mem_packed_dims = mem_vec->packed_dims();

			if (member_comp.index.size() > mem_packed_dims.size()) {
			      cerr << get_fileline() << ": error: "
				   << "Too many index expressions for member." << endl;
			      des->errors += 1;
			      return false;
			}

			  // Evaluate all but the last index expression, into prefix_indices.
			list<long>prefix_indices;
			bool rc = evaluate_index_prefix(des, scope, prefix_indices, member_comp.index);
			ivl_assert(*this, rc);

			if (debug_elaborate) {
			      cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
				   << "prefix_indices.size()==" << prefix_indices.size()
				   << ", mem_packed_dims.size()==" << mem_packed_dims.size()
				   << " (netvector_t context)"
				   << endl;
			}

			long tail_off = 0;
			unsigned long tail_wid = 0;
			rc = calculate_part(this, des, scope, member_comp.index.back(), tail_off, tail_wid);
			ivl_assert(*this, rc);

			if (debug_elaborate) {
			      cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
				   << "calculate_part for tail returns tail_off=" << tail_off
				   << ", tail_wid=" << tail_wid
				   << endl;
			}

			  // Now use the prefix_to_slice function to calculate the
			  // offset and width of the addressed slice of the member.
			long loff;
			unsigned long lwid;
			prefix_to_slice(mem_packed_dims, prefix_indices, tail_off, loff, lwid);

			if (debug_elaborate) {
			      cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
				   << "Calculate loff=" << loff << " lwid=" << lwid
				   << " tail_off=" << tail_off << " tail_wid=" << tail_wid
				   << " off=" << off << " use_width=" << use_width
				   << endl;
			}

			off += loff;
			use_width = lwid * tail_wid;
			member_type = nullptr;
		  }

		    // The netvector_t only has atom elements, to
		    // there is no next struct type.
		  struct_type = 0;

	    } else if (const netparray_t*array = dynamic_cast<const netparray_t*> (member->net_type)) {
		    // If the member is a parray, then the elements
		    // are themselves packed object, including
		    // possibly a struct. Handle this by taking the
		    // part select of the current part of the
		    // variable, then stepping to the element type to
		    // possibly iterate through more of the member_path.

		  ivl_assert(*this, array->packed());
		  ivl_assert(*this, !member_comp.index.empty());

		    // These are the dimensions defined by the type
		  const netranges_t&mem_packed_dims = array->static_dimensions();

		  if (member_comp.index.size() != mem_packed_dims.size()) {
			cerr << get_fileline() << ": error: "
			     << "Incorrect number of index expressions for member "
			     << member_name << "." << endl;
			des->errors += 1;
			return false;
		  }

		    // Evaluate all but the last index expression, into prefix_indices.
		  list<long>prefix_indices;
		  bool rc = evaluate_index_prefix(des, scope, prefix_indices, member_comp.index);
		  ivl_assert(*this, rc);

		  if (debug_elaborate) {
			cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
			     << "prefix_indices.size()==" << prefix_indices.size()
			     << ", mem_packed_dims.size()==" << mem_packed_dims.size()
			     << " (netparray_t context)"
			     << endl;
		  }

		    // Evaluate the last index expression into a constant long.
		  NetExpr*texpr = elab_and_eval(des, scope, member_comp.index.back().msb, -1, true);
		  long tmp;
		  if (texpr == 0 || !eval_as_long(tmp, texpr)) {
			cerr << get_fileline() << ": error: "
			     << "Array index expressions for member " << member_name
			     << " must be constant here." << endl;
			des->errors += 1;
			return false;
		  }

		  delete texpr;

		    // Now use the prefix_to_slice function to calculate the
		    // offset and width of the addressed slice of the member.
		  long loff;
		  unsigned long lwid;
		  prefix_to_slice(mem_packed_dims, prefix_indices, tmp, loff, lwid);

		  ivl_type_t element_type = array->element_type();
		  long element_width = element_type->packed_width();
		  if (debug_elaborate) {
			cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
			     << "parray subselection loff=" << loff
			     << ", lwid=" << lwid
			     << ", element_width=" << element_width
			     << endl;
		  }

		    // The width and offset calculated from the
		    // indices is actually in elements, and not
		    // bits. In fact, in this context, the lwid should
		    // come down to 1 (one element).
		  off += loff * element_width;
		  ivl_assert(*this, lwid==1);
		  use_width = element_width;

		    // To move on to the next component in the member
		    // path, get the element type. For example, for
		    // the path a.b[1].c, we are processing b[1] here,
		    // and the element type should be a netstruct_t
		    // that will wind up containing the member c.
		  struct_type = dynamic_cast<const netstruct_t*> (element_type);

	    } else if (const netstruct_t*tmp_struct = dynamic_cast<const netstruct_t*> (member->net_type)) {
		    // If the member is itself a struct, then get
		    // ready to go on to the next iteration.
		  struct_type = tmp_struct;

	    } else if (const netenum_t*tmp_enum = dynamic_cast<const netenum_t*> (member->net_type)) {
		    // If the element is an enum, then we don't have
		    // anything special to do.
		  if (debug_elaborate) {
			cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
			     << "Tail element is an enum: " << *tmp_enum
			     << endl;
		  }
		  struct_type = 0;

	    } else {
		    // Unknown type?
		  cerr << get_fileline() << ": internal error: "
		       << "Unexpected member type? " << *(member->net_type)
		       << endl;
		  des->errors += 1;
		  return false;
	    }

	      // Complete this component of the path, mark it
	      // completed, and set up for the next component.
	    completed_path .push_back(member_comp);
	    member_path.pop_front();

      } while (!member_path.empty() && struct_type != 0);

      if (debug_elaborate) {
	    cerr << get_fileline() << ": PEIdent::elaborate_lval_net_packed_member_: "
		 << "After processing member_path, "
		 << "off=" << off
		 << ", use_width=" << use_width
		 << ", completed_path=" << completed_path
		 << ", member_path=" << member_path
		 << endl;
      }

	// The dimensions in the expression must match the packed
	// dimensions that are declared for the variable. For example,
	// if foo is a packed array of struct, then this expression
	// must be "b[n][m]" with the right number of dimensions to
	// match the declaration of "b".
	// Note that one of the packed dimensions is the packed struct
	// itself.
      ivl_assert(*this, name_base.index.size()+1 == reg->packed_dimensions());

	// Generate an expression that takes the input array of
	// expressions and generates a canonical offset into the
	// packed array.
      NetExpr*packed_base = 0;
      if (reg->packed_dimensions() > 1) {
	    list<index_component_t>tmp_index = name_base.index;
	    index_component_t member_select;
	    member_select.sel = index_component_t::SEL_BIT;
	    member_select.msb = new PENumber(new verinum(off));
	    tmp_index.push_back(member_select);
	    packed_base = collapse_array_indices(des, scope, reg, tmp_index);
      }

      long tmp;
      if (packed_base && eval_as_long(tmp, packed_base)) {
	    off = tmp;
	    delete packed_base;
	    packed_base = 0;
      }

      if (reg->type()==NetNet::UNRESOLVED_WIRE) {
	    cerr << get_fileline() << ": error: "
		 << path_ << " Unable to member-select unresolved wires."
		 << endl;
	    des->errors += 1;
	    return false;
      }

      if (packed_base == 0) {
	    NetExpr *base = new NetEConst(verinum(off));
	    if (member_type)
		  lv->set_part(base, member_type);
	    else
		  lv->set_part(base, use_width);
	    return true;
      }

	// Oops, packed_base is not fully evaluated, so I don't know
	// yet what to do with it.
      cerr << get_fileline() << ": internal error: "
	   << "I don't know how to handle this index expression? " << *packed_base << endl;
      ivl_assert(*this, 0);
      return false;
}

NetAssign_* PENumber::elaborate_lval(Design*des, NetScope*, bool, bool, bool) const
{
      cerr << get_fileline() << ": error: Constant values not allowed "
	   << "in l-value expressions." << endl;
      des->errors += 1;
      return 0;
}