Calculate the dominators of each node in the flow graph.

The dominators are represented by sets using the node numbers.

tools/qfcc/include/flow.h

@@ -45,6 +45,7 @@ int flow_is_return (struct statement_s *s);
 struct sblock_s *flow_get_target (struct statement_s *s);
 void flow_build_vars (struct function_s *func);
 void flow_build_graph (struct function_s *func);
+void flow_calc_dominators (struct function_s *func);
 
 //@}
 

tools/qfcc/include/statements.h

@@ -81,6 +81,7 @@ typedef struct sblock_s {
 	int         number;			///< number of this block in flow graph
 	statement_t *statements;
 	statement_t **tail;
+	struct set_s *dom;			///< set of nodes that dominate this node
 } sblock_t;
 
 struct expr_s;

tools/qfcc/source/flow.c

@@ -44,6 +44,7 @@
 #include "dags.h"
 #include "flow.h"
 #include "function.h"
+#include "set.h"
 #include "statements.h"
 #include "symtab.h"
 
@@ -226,3 +227,42 @@ flow_build_graph (function_t *func)
 		}
 	}
 }
+
+void
+flow_calc_dominators (function_t *func)
+{
+	set_t      *work;
+	sblock_t  **pred;
+	int         i;
+	int         changed;
+
+	if (!func->num_nodes)
+		return;
+
+	// First, create a base set for the initial state of the non-initial nodes
+	work = set_new ();
+	for (i = 0; i < func->num_nodes; i++)
+		set_add (work, i);
+
+	func->graph[0]->dom = set_new ();
+	set_add (func->graph[0]->dom, 0);
+
+	// initialize dom for the non-initial nodes
+	for (i = 1; i < func->num_nodes; i++) {
+		func->graph[i]->dom = set_new ();
+		set_assign (func->graph[i]->dom, work);
+	}
+
+	do {
+		changed = 0;
+		for (i = 1; i < func->num_nodes; i++) {
+			set_assign (work, func->graph[i]->pred[0]->dom);
+			for (pred = func->graph[i]->pred + 1; *pred; pred++)
+				set_intersection (work, (*pred)->dom);
+			set_add (work, i);
+			if (!set_is_equivalent (work, func->graph[i]->dom))
+				changed = 1;
+			set_assign (func->graph[i]->dom, work);
+		}
+	} while (changed);
+}

tools/qfcc/source/function.c

@@ -645,6 +645,7 @@ emit_function (function_t *f, expr_t *e)
 	f->sblock = make_statements (e);
 	flow_build_vars (f);
 	flow_build_graph (f);
+	flow_calc_dominators (f);
 	if (options.block_dot.flow)
 		print_flow (f->sblock, nva ("%s.%s.%s.dot", GETSTR (pr.source_file),
 									f->name, "flow"));