+// Traverse the program, discovering the functions that are roots of strongly
+// connected components. The goal of this phase to produce a set of functions
+// that must be analyzed in order.
+
+class Escape_analysis_discover : public Traverse
+{
+ public:
+ Escape_analysis_discover(Gogo* gogo)
+ : Traverse(traverse_functions),
+ gogo_(gogo), component_ids_()
+ { }
+
+ int
+ function(Named_object*);
+
+ int
+ visit(Named_object*);
+
+ int
+ visit_code(Named_object*, int);
+
+ private:
+ // A counter used to generate the ID for the function node in the graph.
+ static int id;
+
+ // Type used to map functions to an ID in a graph of connected components.
+ typedef Unordered_map(Named_object*, int) Component_ids;
+
+ // The Go IR.
+ Gogo* gogo_;
+ // The list of functions encountered during connected component discovery.
+ Component_ids component_ids_;
+ // The stack of functions that this component consists of.
+ std::stack<Named_object*> stack_;
+};
+
+int Escape_analysis_discover::id = 0;
+
+// Visit each function.
+
+int
+Escape_analysis_discover::function(Named_object* fn)
+{
+ this->visit(fn);
+ return TRAVERSE_CONTINUE;
+}
+
+// Visit a function FN, adding it to the current stack of functions
+// in this connected component. If this is the root of the component,
+// create a set of functions to be analyzed later.
+//
+// Finding these sets is finding strongly connected components
+// in the static call graph. The algorithm for doing that is taken
+// from Sedgewick, Algorithms, Second Edition, p. 482, with two
+// adaptations.
+//
+// First, a closure (fn->func_value()->enclosing() == NULL) cannot be the
+// root of a connected component. Refusing to use it as a root
+// forces it into the component of the function in which it appears.
+// This is more convenient for escape analysis.
+//
+// Second, each function becomes two virtual nodes in the graph,
+// with numbers n and n+1. We record the function's node number as n
+// but search from node n+1. If the search tells us that the component
+// number (min) is n+1, we know that this is a trivial component: one function
+// plus its closures. If the search tells us that the component number is
+// n, then there was a path from node n+1 back to node n, meaning that
+// the function set is mutually recursive. The escape analysis can be
+// more precise when analyzing a single non-recursive function than
+// when analyzing a set of mutually recursive functions.
+
+int
+Escape_analysis_discover::visit(Named_object* fn)
+{
+ Component_ids::const_iterator p = this->component_ids_.find(fn);
+ if (p != this->component_ids_.end())
+ // Already visited.
+ return p->second;
+
+ this->id++;
+ int id = this->id;
+ this->component_ids_[fn] = id;
+ this->id++;
+ int min = this->id;
+
+ this->stack_.push(fn);
+ min = this->visit_code(fn, min);
+ if ((min == id || min == id + 1)
+ && fn->is_function()
+ && fn->func_value()->enclosing() == NULL)
+ {
+ bool recursive = min == id;
+ std::vector<Named_object*> group;
+
+ for (; !this->stack_.empty(); this->stack_.pop())
+ {
+ Named_object* n = this->stack_.top();
+ if (n == fn)
+ {
+ this->stack_.pop();
+ break;
+ }
+
+ group.push_back(n);
+ this->component_ids_[n] = std::numeric_limits<int>::max();
+ }
+ group.push_back(fn);
+ this->component_ids_[fn] = std::numeric_limits<int>::max();
+
+ std::reverse(group.begin(), group.end());
+ this->gogo_->add_analysis_set(group, recursive);
+ }
+
+ return min;
+}
+
+// Helper class for discovery step. Traverse expressions looking for
+// function calls and closures to visit during the discovery step.
+
+class Escape_discover_expr : public Traverse
+{
+ public:
+ Escape_discover_expr(Escape_analysis_discover* ead, int min)
+ : Traverse(traverse_expressions),
+ ead_(ead), min_(min)
+ { }
+
+ int
+ min()
+ { return this->min_; }
+
+ int
+ expression(Expression** pexpr);
+
+ private:
+ // The original discovery analysis.
+ Escape_analysis_discover* ead_;
+ // The minimum component ID in this group.
+ int min_;
+};
+
+// Visit any calls or closures found when discovering expressions.
+
+int
+Escape_discover_expr::expression(Expression** pexpr)
+{
+ Expression* e = *pexpr;
+ Named_object* fn = NULL;
+ if (e->call_expression() != NULL
+ && e->call_expression()->fn()->func_expression() != NULL)
+ {
+ // Method call or function call.
+ fn = e->call_expression()->fn()->func_expression()->named_object();
+ }
+ else if (e->func_expression() != NULL
+ && e->func_expression()->closure() != NULL)
+ {
+ // Closure.
+ fn = e->func_expression()->named_object();
+ }
+
+ if (fn != NULL)
+ this->min_ = std::min(this->min_, this->ead_->visit(fn));
+ return TRAVERSE_CONTINUE;
+}
+
+// Visit the body of each function, returns ID of the minimum connected
+// component found in the body.
+
+int
+Escape_analysis_discover::visit_code(Named_object* fn, int min)
+{
+ if (!fn->is_function())
+ return min;
+
+ Escape_discover_expr ede(this, min);
+ fn->func_value()->traverse(&ede);
+ return ede.min();
+}
+
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