Fix expression type for compressed assignment statements.

A compressed assignment statement should give exactly the same
result as the equivalent uncompressed statement. This means
that the type (signed/unsigned) of the LHS affects the type of
the RHS expression (unlike in normal assignments). We need to
take care that bit/part selects and concatenations are correctly
identified as unsigned values, even in the cases where they
reduce to a single whole signal.

Statement.h

@@ -108,7 +108,8 @@ class PAssign_  : public Statement {
       NetAssign_* elaborate_lval(Design*, NetScope*scope) const;
       NetExpr* elaborate_rval_(Design*, NetScope*, ivl_type_t lv_net_type,
 			       ivl_variable_type_t lv_type,
-			       unsigned lv_width) const;
+			       unsigned lv_width,
+			       bool force_unsigned =false) const;
       NetExpr* elaborate_rval_(Design*, NetScope*, ivl_type_t ntype) const;
 
       NetExpr* elaborate_rval_obj_(Design*, NetScope*,

elab_expr.cc

@@ -90,7 +90,7 @@ static NetBranch* find_existing_implicit_branch(NetNet*sig, NetNet*gnd)
 
 NetExpr* elaborate_rval_expr(Design*des, NetScope*scope, ivl_type_t lv_net_type,
 			     ivl_variable_type_t lv_type, unsigned lv_width,
-			     PExpr*expr, bool need_const)
+			     PExpr*expr, bool need_const, bool force_unsigned)
 {
       if (debug_elaborate) {
 	    cerr << expr->get_fileline() << ": elaborate_rval_expr: "
@@ -135,7 +135,7 @@ NetExpr* elaborate_rval_expr(Design*des, NetScope*scope, ivl_type_t lv_net_type,
       }
 
       return elab_and_eval(des, scope, expr, context_wid, need_const,
-			   false, lv_type);
+			   false, lv_type, force_unsigned);
 }
 
 /*

elab_lval.cc

@@ -138,6 +138,9 @@ NetAssign_* PEConcat::elaborate_lval(Design*des,
 		  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)
@@ -399,6 +402,7 @@ NetAssign_* PEIdent::elaborate_lval(Design*des,
 	/* No select expressions. */
 
       NetAssign_*lv = new NetAssign_(reg);
+      lv->set_signed(reg->get_signed());
 
       return lv;
 }

elaborate.cc

@@ -2307,7 +2307,8 @@ NetExpr* PAssign_::elaborate_rval_(Design*des, NetScope*scope,
 NetExpr* PAssign_::elaborate_rval_(Design*des, NetScope*scope,
 				   ivl_type_t lv_net_type,
 				   ivl_variable_type_t lv_type,
-				   unsigned lv_width) const
+				   unsigned lv_width,
+				   bool force_unsigned) const
 {
       ivl_assert(*this, rval_);
 
@@ -2316,7 +2317,7 @@ NetExpr* PAssign_::elaborate_rval_(Design*des, NetScope*scope,
 	// should look into fixing calls to this method to pass a
 	// net_type instead of the separate lv_width/lv_type values.
       NetExpr*rv = elaborate_rval_expr(des, scope, lv_net_type, lv_type, lv_width,
-				       rval(), is_constant_);
+				       rval(), is_constant_, force_unsigned);
 
       if (!is_constant_ || !rv) return rv;
 
@@ -2434,7 +2435,12 @@ NetProc* PAssign::elaborate_compressed_(Design*des, NetScope*scope) const
       NetAssign_*lv = elaborate_lval(des, scope);
       if (lv == 0) return 0;
 
-      NetExpr*rv = elaborate_rval_(des, scope, 0, lv->expr_type(), count_lval_width(lv));
+	// Compressed assignments should behave identically to the
+	// equivalent uncompressed assignments. This means we need
+	// to take the type of the LHS into account when determining
+	// the type of the RHS expression.
+      NetExpr*rv = elaborate_rval_(des, scope, 0, lv->expr_type(),
+				   count_lval_width(lv), !lv->get_signed());
       if (rv == 0) return 0;
 
       NetAssign*cur = new NetAssign(lv, op_, rv);

net_assign.cc

@@ -44,6 +44,7 @@ NetAssign_::NetAssign_(NetAssign_*n)
 {
       lwid_ = 0;
       more = 0;
+      signed_ = false;
       turn_sig_to_wire_on_release_ = false;
 }
 
@@ -53,6 +54,7 @@ NetAssign_::NetAssign_(NetNet*s)
       lwid_ = sig_->vector_width();
       sig_->incr_lref();
       more = 0;
+      signed_ = false;
       turn_sig_to_wire_on_release_ = false;
 }
 

netlist.h

@@ -2764,6 +2764,12 @@ class NetAssign_ {
       void set_property(const perm_string&name);
       inline perm_string get_property(void) const { return member_; }
 
+	// Determine if the assigned object is signed or unsigned.
+	// This is used when determining the expression type for
+	// a compressed assignment statement.
+      bool get_signed() const { return signed_; }
+      void set_signed(bool flag) { signed_ = flag; }
+
 	// Get the width of the r-value that this node expects. This
 	// method accounts for the presence of the mux, so it is not
 	// necessarily the same as the pin_count().
@@ -2814,6 +2820,7 @@ class NetAssign_ {
 	// member/property if signal is a class.
       perm_string member_;
 
+      bool signed_;
       bool turn_sig_to_wire_on_release_;
 	// indexed part select base
       NetExpr*base_;

netmisc.cc

@@ -802,9 +802,10 @@ NetExpr* condition_reduce(NetExpr*expr)
 }
 
 static NetExpr* do_elab_and_eval(Design*des, NetScope*scope, PExpr*pe,
-				 int context_width, bool need_const, bool annotatable,
-				 bool force_expand,
-				 ivl_variable_type_t cast_type)
+				 int context_width, bool need_const,
+				 bool annotatable, bool force_expand,
+				 ivl_variable_type_t cast_type,
+				 bool force_unsigned)
 {
       PExpr::width_mode_t mode = PExpr::SIZED;
       if ((context_width == -2) && !gn_strict_expr_width_flag)
@@ -824,6 +825,11 @@ static NetExpr* do_elab_and_eval(Design*des, NetScope*scope, PExpr*pe,
       if ((pe->expr_type() != IVL_VT_REAL) && (expr_width < pos_context_width))
             expr_width = pos_context_width;
 
+	// If this is the RHS of a compressed assignment, the LHS also
+	// affects the expression type (signed/unsigned).
+      if (force_unsigned)
+	    pe->cast_signed(false);
+
       if (debug_elaborate) {
             cerr << pe->get_fileline() << ": elab_and_eval: test_width of "
                  << *pe << endl;
@@ -910,10 +916,11 @@ static NetExpr* do_elab_and_eval(Design*des, NetScope*scope, PExpr*pe,
 
 NetExpr* elab_and_eval(Design*des, NetScope*scope, PExpr*pe,
 		       int context_width, bool need_const, bool annotatable,
-		       ivl_variable_type_t cast_type)
+		       ivl_variable_type_t cast_type, bool force_unsigned)
 {
       return do_elab_and_eval(des, scope, pe, context_width,
-			      need_const, annotatable, false, cast_type);
+			      need_const, annotatable, false,
+			      cast_type, force_unsigned);
 }
 
 /*
@@ -926,7 +933,8 @@ NetExpr* elab_and_eval_lossless(Design*des, NetScope*scope, PExpr*pe,
 				 ivl_variable_type_t cast_type)
 {
       return do_elab_and_eval(des, scope, pe, context_width,
-			      need_const, annotatable, true, cast_type);
+			      need_const, annotatable, true,
+			      cast_type, false);
 }
 
 NetExpr* elab_and_eval(Design*des, NetScope*scope, PExpr*pe,

netmisc.h

@@ -258,7 +258,8 @@ extern NetExpr* elab_and_eval(Design*des, NetScope*scope,
 			      PExpr*pe, int context_width,
                               bool need_const =false,
                               bool annotatable =false,
-			      ivl_variable_type_t cast_type =IVL_VT_NO_TYPE);
+			      ivl_variable_type_t cast_type =IVL_VT_NO_TYPE,
+			      bool force_unsigned =false);
 
 extern NetExpr* elab_and_eval_lossless(Design*des, NetScope*scope,
 			      PExpr*pe, int context_width,
@@ -297,7 +298,8 @@ extern NetExpr* elaborate_rval_expr(Design*des, NetScope*scope,
 				    ivl_type_t lv_net_type,
 				    ivl_variable_type_t lv_type,
 				    unsigned lv_width, PExpr*expr,
-                                    bool need_const =false);
+				    bool need_const =false,
+				    bool force_unsigned =false);
 
 extern bool evaluate_ranges(Design*des, NetScope*scope,
 			    std::vector<netrange_t>&llist,