Introduce assign_modify_operation

This adds class assign_modify_operation, which implements
BINOP_ASSIGN_MODIFY.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expop.h (class assign_modify_operation): New.
	* eval.c (eval_binop_assign_modify): No longer static.
	* ax-gdb.c (assign_modify_operation::do_generate_ax): New method.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2021-03-08  Tom Tromey  <tom@tromey.com>
+
+	* expop.h (class assign_modify_operation): New.
+	* eval.c (eval_binop_assign_modify): No longer static.
+	* ax-gdb.c (assign_modify_operation::do_generate_ax): New method.
+
 2021-03-08  Tom Tromey  <tom@tromey.com>
 
 	* expop.h (class assign_operation): New.

gdb/ax-gdb.c

@@ -2609,6 +2609,48 @@ assign_operation::do_generate_ax (struct expression *exp,
 	     "may not assign to it"), name);
 }
 
+void
+assign_modify_operation::do_generate_ax (struct expression *exp,
+					 struct agent_expr *ax,
+					 struct axs_value *value,
+					 struct type *cast_type)
+{
+  operation *subop = std::get<1> (m_storage).get ();
+  if (subop->opcode () != OP_INTERNALVAR)
+    error (_("May only assign to trace state variables"));
+
+  internalvar_operation *ivarop
+    = dynamic_cast<internalvar_operation *> (subop);
+  gdb_assert (ivarop != nullptr);
+
+  const char *name = internalvar_name (ivarop->get_internalvar ());
+  struct trace_state_variable *tsv;
+
+  tsv = find_trace_state_variable (name);
+  if (tsv)
+    {
+      /* The tsv will be the left half of the binary operation.  */
+      ax_tsv (ax, aop_getv, tsv->number);
+      if (ax->tracing)
+	ax_tsv (ax, aop_tracev, tsv->number);
+      /* Trace state variables are always 64-bit integers.  */
+      struct axs_value value1, value2;
+      value1.kind = axs_rvalue;
+      value1.type = builtin_type (ax->gdbarch)->builtin_long_long;
+      /* Now do right half of expression.  */
+      std::get<2> (m_storage)->generate_ax (exp, ax, &value2);
+      gen_expr_binop_rest (exp, std::get<0> (m_storage), ax,
+			   value, &value1, &value2);
+      /* We have a result of the binary op, set the tsv.  */
+      ax_tsv (ax, aop_setv, tsv->number);
+      if (ax->tracing)
+	ax_tsv (ax, aop_tracev, tsv->number);
+    }
+  else
+    error (_("$%s is not a trace state variable, "
+	     "may not assign to it"), name);
+}
+
 }
 
 /* This handles the middle-to-right-side of code generation for binary

gdb/eval.c

@@ -2074,7 +2074,7 @@ eval_op_type (struct type *expect_type, struct expression *exp,
 
 /* A helper function for BINOP_ASSIGN_MODIFY.  */
 
-static struct value *
+struct value *
 eval_binop_assign_modify (struct type *expect_type, struct expression *exp,
 			  enum noside noside, enum exp_opcode op,
 			  struct value *arg1, struct value *arg2)

gdb/expop.h

@@ -197,6 +197,12 @@ extern struct value *eval_op_memval (struct type *expect_type,
 				     struct expression *exp,
 				     enum noside noside,
 				     struct value *arg1, struct type *type);
+extern struct value *eval_binop_assign_modify (struct type *expect_type,
+					       struct expression *exp,
+					       enum noside noside,
+					       enum exp_opcode op,
+					       struct value *arg1,
+					       struct value *arg2);
 
 namespace expr
 {
@@ -1800,6 +1806,36 @@ protected:
     override;
 };
 
+/* Assignment with modification, like "+=".  */
+class assign_modify_operation
+  : public tuple_holding_operation<exp_opcode, operation_up, operation_up>
+{
+public:
+
+  using tuple_holding_operation::tuple_holding_operation;
+
+  value *evaluate (struct type *expect_type,
+		   struct expression *exp,
+		   enum noside noside) override
+  {
+    value *lhs = std::get<1> (m_storage)->evaluate (nullptr, exp, noside);
+    value *rhs = std::get<2> (m_storage)->evaluate (expect_type, exp, noside);
+    return eval_binop_assign_modify (expect_type, exp, noside,
+				     std::get<0> (m_storage), lhs, rhs);
+  }
+
+  enum exp_opcode opcode () const override
+  { return BINOP_ASSIGN_MODIFY; }
+
+protected:
+
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override;
+};
+
 } /* namespace expr */
 
 #endif /* EXPOP_H */