Add support for const variables

PExpr.h

@@ -172,7 +172,8 @@ class PExpr : public LineInfo {
  virtual NetAssign_* elaborate_lval(Design*des,
  NetScope*scope,
  bool is_cassign,
- bool is_force) const;
+ bool is_force,
+ bool is_init = false) const;
 
  // This method returns true if the expression represents a
  // structural net that can have multiple drivers. This is
@@ -262,7 +263,8 @@ class PEConcat : public PExpr {
  virtual NetAssign_* elaborate_lval(Design*des,
  NetScope*scope,
  bool is_cassign,
- bool is_force) const;
+ bool is_force,
+ bool is_init = false) const;
  virtual bool is_collapsible_net(Design*des, NetScope*scope,
  NetNet::PortType port_type) const;
  private:
@@ -361,7 +363,8 @@ class PEIdent : public PExpr {
  virtual NetAssign_* elaborate_lval(Design*des,
  NetScope*scope,
  bool is_cassign,
- bool is_force) const;
+ bool is_force,
+ bool is_init = false) const;
 
  virtual NetExpr*elaborate_expr(Design*des, NetScope*scope,
  ivl_type_t type, unsigned flags) const;
@@ -647,7 +650,8 @@ class PENumber : public PExpr {
  virtual NetAssign_* elaborate_lval(Design*des,
  NetScope*scope,
  bool is_cassign,
- bool is_force) const;
+ bool is_force,
+ bool is_init = false) const;
 
  private:
  verinum*const value_;

PWire.h

@@ -68,6 +68,9 @@ class PWire : public PNamedItem {
  NetNet::PortType get_port_type() const;
  bool set_port_type(NetNet::PortType);
 
+ void set_const(bool is_const) { is_const_ = is_const; };
+ bool get_const() const { return is_const_; };
+
  void set_signed(bool flag);
  bool get_signed() const;
 
@@ -100,6 +103,9 @@ class PWire : public PNamedItem {
  NetNet::PortType port_type_;
  bool signed_;
 
+ // Whether the wire is variable declared with the const keyword.
+ bool is_const_ = false;
+
  // These members hold expressions for the bit width of the
  // wire. If they do not exist, the wire is 1 bit wide. If they
  // do exist, they represent the packed dimensions of the

Statement.cc

@@ -29,8 +29,9 @@ Statement::~Statement()
 {
 }
 
-PAssign_::PAssign_(PExpr*lval__, PExpr*ex, bool is_constant)
-: event_(0), count_(0), lval_(lval__), rval_(ex), is_constant_(is_constant)
+PAssign_::PAssign_(PExpr*lval__, PExpr*ex, bool is_constant, bool is_init)
+: event_(0), count_(0), lval_(lval__), rval_(ex), is_constant_(is_constant),
+ is_init_(is_init)
 {
  delay_ = 0;
 }
@@ -73,8 +74,8 @@ PAssign::PAssign(PExpr*lval__, PExpr*cnt, PEventStatement*d, PExpr*ex)
 {
 }
 
-PAssign::PAssign(PExpr*lval__, PExpr*ex, bool is_constant)
-: PAssign_(lval__, ex, is_constant), op_(0)
+PAssign::PAssign(PExpr*lval__, PExpr*ex, bool is_constant, bool is_init)
+: PAssign_(lval__, ex, is_constant, is_init), op_(0)
 {
 }
 

Statement.h

@@ -95,7 +95,8 @@ class Statement : virtual public LineInfo {
  */
 class PAssign_ : public Statement {
  public:
- explicit PAssign_(PExpr*lval, PExpr*ex, bool is_constant);
+ explicit PAssign_(PExpr*lval, PExpr*ex, bool is_constant,
+ bool is_init = false);
  explicit PAssign_(PExpr*lval, PExpr*de, PExpr*ex);
  explicit PAssign_(PExpr*lval, PExpr*cnt, PEventStatement*de, PExpr*ex);
  virtual ~PAssign_() =0;
@@ -122,6 +123,8 @@ class PAssign_ : public Statement {
  PExpr* lval_;
  PExpr* rval_;
  bool is_constant_;
+ // Whether the assignment is a variable initializer expression
+ bool is_init_ = false;
 };
 
 class PAssign : public PAssign_ {
@@ -135,7 +138,7 @@ class PAssign : public PAssign_ {
  explicit PAssign(PExpr*lval, char op, PExpr*ex);
  explicit PAssign(PExpr*lval, PExpr*de, PExpr*ex);
  explicit PAssign(PExpr*lval, PExpr*cnt, PEventStatement*de, PExpr*ex);
- explicit PAssign(PExpr*lval, PExpr*ex, bool is_constant);
+ explicit PAssign(PExpr*lval, PExpr*ex, bool is_constant, bool is_init);
  ~PAssign();
 
  virtual void dump(std::ostream&out, unsigned ind) const;

elab_lval.cc

@@ -76,7 +76,7 @@ using namespace std;
  * 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) const
+NetAssign_* PExpr::elaborate_lval(Design*, NetScope*, bool, bool, bool) const
 {
  cerr << get_fileline() << ": Assignment l-value too complex." << endl;
  return 0;
@@ -98,7 +98,8 @@ NetAssign_* PExpr::elaborate_lval(Design*, NetScope*, bool, bool) const
 NetAssign_* PEConcat::elaborate_lval(Design*des,
  NetScope*scope,
  bool is_cassign,
- bool is_force) const
+ bool is_force,
+ bool is_init) const
 {
  if (repeat_) {
  cerr << get_fileline() << ": error: Repeat concatenations make "
@@ -119,7 +120,7 @@ NetAssign_* PEConcat::elaborate_lval(Design*des,
  }
 
  NetAssign_*tmp = parms_[idx]->elaborate_lval(des, scope,
- is_cassign, is_force);
+ 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
@@ -157,7 +158,8 @@ NetAssign_* PEConcat::elaborate_lval(Design*des,
 NetAssign_* PEIdent::elaborate_lval(Design*des,
  NetScope*scope,
  bool is_cassign,
- bool is_force) const
+ bool is_force,
+ bool is_init) const
 {
 
  if (debug_elaborate) {
@@ -213,6 +215,13 @@ NetAssign_* PEIdent::elaborate_lval(Design*des,
  << 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);
 }
@@ -1535,7 +1544,7 @@ bool PEIdent::elaborate_lval_net_packed_member_(Design*des, NetScope*scope,
  return false;
 }
 
-NetAssign_* PENumber::elaborate_lval(Design*des, NetScope*, bool, bool) const
+NetAssign_* PENumber::elaborate_lval(Design*des, NetScope*, bool, bool, bool) const
 {
  cerr << get_fileline() << ": error: Constant values not allowed "
  << "in l-value expressions." << endl;

elab_net.cc

@@ -556,6 +556,12 @@ NetNet* PEIdent::elaborate_lnet_common_(Design*des, NetScope*scope,
  << endl;
  }
 
+ if (sig->get_const()) {
+ cerr << get_fileline() << ": error: Continuous assignment to const"
+ << " signal `" << sig->name() << "` is not allowed." << endl;
+ des->errors++;
+ return nullptr;
+ }
 
  // If this is SystemVerilog and the variable is not yet
  // assigned by anything, then convert it to an unresolved

elab_sig.cc

@@ -1204,5 +1204,7 @@ NetNet* PWire::elaborate_sig(Design*des, NetScope*scope) const
  for (unsigned idx = 0 ; idx < nattrib ; idx += 1)
  sig->attribute(attrib_list[idx].key, attrib_list[idx].val);
 
+ sig->set_const(is_const_);
+
  return sig;
 }

elaborate.cc

@@ -2378,7 +2378,7 @@ NetAssign_* PAssign_::elaborate_lval(Design*des, NetScope*scope) const
  << "lval_ expr type = " << typeid(*lval_).name() << endl;
  }
 
- return lval_->elaborate_lval(des, scope, false, false);
+ return lval_->elaborate_lval(des, scope, false, false, is_init_);
 }
 
 NetExpr* PAssign_::elaborate_rval_(Design*des, NetScope*scope,

ivtest/ivltests/sv_const1.v

@@ -0,0 +1,18 @@
+// Check that const variables in module scope are supported.
+
+module test;
+
+ const integer x = 10;
+
+ // The initializer expression is allowed to reference other const variables.
+ const integer y = 20 + x;
+
+ initial begin
+ if (x === 10 && y === 30) begin
+ $display("PASSED");
+ end else begin
+ $display("FAILED");
+ end
+ end
+
+endmodule

ivtest/ivltests/sv_const2.v

@@ -0,0 +1,29 @@
+// Check that const variables are supported in function and task scope.
+
+module test;
+
+ function automatic integer f(integer x);
+ // Automatic const variables can have a non-const initializer epxression
+ const integer y = 2 * x;
+ return y;
+ endfunction
+
+ task automatic t(input integer x, output integer y);
+ // Automatic const variables can have a non-const initializer epxression
+ const integer z = 2 * x;
+ y = z;
+ endtask
+
+ initial begin
+ integer y;
+
+ t(15, y);
+
+ if (f(10) === 20 && y === 30) begin
+ $display("PASSED");
+ end else begin
+ $display("FAILED");
+ end
+ end
+
+endmodule

ivtest/ivltests/sv_const3.v

@@ -0,0 +1,17 @@
+// Check that const variables in block scope are supported.
+
+module test;
+
+ initial begin
+ const static integer x = 10;
+ // The initializer expression is allowed to reference other const variables.
+ const static integer y = 20 + x;
+
+ if (x === 10 && y === 30) begin
+ $display("PASSED");
+ end else begin
+ $display("FAILED");
+ end
+ end
+
+endmodule

ivtest/ivltests/sv_const4.v

@@ -0,0 +1,18 @@
+// Check that const variables are supported in the unit scope.
+
+const integer x = 10;
+
+// The initializer expression is allowed to reference other const variables.
+const integer y = 20 + x;
+
+module test;
+
+ initial begin
+ if (x === 10 && y === 30) begin
+ $display("PASSED");
+ end else begin
+ $display("FAILED");
+ end
+ end
+
+endmodule

ivtest/ivltests/sv_const5.v

@@ -0,0 +1,20 @@
+// Check that const variables are supported in a package scope.
+
+package P;
+ const integer x = 10;
+
+ // The initializer expression is allowed to reference other const variables.
+ const integer y = 20 + x;
+endpackage
+
+module test;
+
+ initial begin
+ if (P::x === 10 && P::y === 30) begin
+ $display("PASSED");
+ end else begin
+ $display("FAILED");
+ end
+ end
+
+endmodule

ivtest/ivltests/sv_const_fail1.v

@@ -0,0 +1,13 @@
+// Check that continuous assignment to a const variable fails.
+
+module test;
+
+ const integer x = 10;
+
+ assign x = 20; // Error: Assignment to const variable
+
+ initial begin
+ $display("FAILED");
+ end
+
+endmodule

ivtest/ivltests/sv_const_fail2.v

@@ -0,0 +1,12 @@
+// Check that blocking assignment to a const variable fails.
+
+module test;
+
+ const integer x = 10;
+
+ initial begin
+ x = 20; // Error: Assignment to const variable
+ $display("FAILED");
+ end
+
+endmodule

ivtest/ivltests/sv_const_fail3.v

@@ -0,0 +1,12 @@
+// Check that non-blocking assignment to a const variable fails.
+
+module test;
+
+ const integer x = 10;
+
+ initial begin
+ x <= 20; // Error: Assignment to const variable
+ $display("FAILED");
+ end
+
+endmodule

ivtest/ivltests/sv_const_fail4.v

@@ -0,0 +1,12 @@
+// Check that force assignment to a const variable fails.
+
+module test;
+
+ const integer x = 10;
+
+ initial begin
+ force x = 20; // Error: Assignment to const variable
+ $display("FAILED");
+ end
+
+endmodule

ivtest/ivltests/sv_const_fail5.v

@@ -0,0 +1,12 @@
+// Check that procedural continuous assignment to a const variable fails.
+
+module test;
+
+ const integer x = 10;
+
+ initial begin
+ assign x = 20; // Error: Assignment to const variable
+ $display("FAILED");
+ end
+
+endmodule

ivtest/ivltests/sv_const_fail6.v

@@ -0,0 +1,16 @@
+// Check that binding a const variable to a task output port fails.
+
+module test;
+
+ const integer x = 10;
+
+ task t(output integer x);
+ x = 20;
+ endtask
+
+ initial begin
+ t(x);
+ $display("FAILED");
+ end
+
+endmodule