tailrec requires many Returns

Extend opt_manage framework with MANY_RETURNS condition.

Since normalize_n_returns might introduce unreachable code,
the order should be handled in the framework instead of the
optimization.

Fix opt/gap test.

include/libfirm/irgraph.h

@@ -462,6 +462,8 @@ typedef enum {
 	IR_GRAPH_STATE_CONSISTENT_ENTITY_USAGE   = 1U << 14,
 	/** extended basic blocks have been formed and are up to date */
 	IR_GRAPH_STATE_VALID_EXTENDED_BLOCKS     = 1U << 15,
+	/** graph contains as many returns as possible */
+	IR_GRAPH_STATE_MANY_RETURNS              = 1U << 16,
 } ir_graph_state_t;
 ENUM_BITSET(ir_graph_state_t)
 

ir/opt/opt_manage.c

@@ -25,9 +25,13 @@ void perform_irg_optimization(ir_graph *irg, optdesc_t *opt)
 	ir_graph_state_t required = opt->requirements;
 	const bool dump = get_irp_optimization_dumps();
 
+	/* It does not make sense to require both: */
+	assert (!((required & IR_GRAPH_STATE_ONE_RETURN) && (required & IR_GRAPH_STATE_MANY_RETURNS)));
+
 	/* assure that all requirements for the optimization are fulfilled */
 #define PREPARE(st,func) if (st & (required ^ irg->state)) {func(irg); set_irg_state(irg,st);}
 	PREPARE(IR_GRAPH_STATE_ONE_RETURN,               normalize_one_return)
+	PREPARE(IR_GRAPH_STATE_MANY_RETURNS,             normalize_n_returns)
 	PREPARE(IR_GRAPH_STATE_NO_CRITICAL_EDGES,        remove_critical_cf_edges)
 	PREPARE(IR_GRAPH_STATE_NO_UNREACHABLE_CODE,      remove_unreachable_code)
 	PREPARE(IR_GRAPH_STATE_NO_BADS,                  remove_bads)
@@ -57,6 +61,7 @@ void perform_irg_optimization(ir_graph *irg, optdesc_t *opt)
 	INVALIDATE(IR_GRAPH_STATE_NO_UNREACHABLE_CODE,      nop)
 	INVALIDATE(IR_GRAPH_STATE_NO_BADS,                  nop)
 	INVALIDATE(IR_GRAPH_STATE_ONE_RETURN,               nop)
+	INVALIDATE(IR_GRAPH_STATE_MANY_RETURNS,             nop)
 	INVALIDATE(IR_GRAPH_STATE_CONSISTENT_DOMINANCE,     nop)
 	INVALIDATE(IR_GRAPH_STATE_CONSISTENT_POSTDOMINANCE, nop)
 	INVALIDATE(IR_GRAPH_STATE_CONSISTENT_OUTS,          nop)

ir/opt/tailrec.c

@@ -594,12 +594,6 @@ static ir_graph_state_t do_tailrec(ir_graph *irg)
 			env.variants[i] = TR_DIRECT;
 	}
 
-	/*
-	 * This tail recursion optimization works best
-	 * if the Returns are normalized.
-	 */
-	normalize_n_returns(irg);
-
 	ir_reserve_resources(irg, IR_RESOURCE_IRN_LINK);
 
 	end_block = get_irg_end_block(irg);
@@ -661,7 +655,7 @@ static ir_graph_state_t do_tailrec(ir_graph *irg)
 				break;
 			}
 			if (var == TR_DIRECT)
-				var = env.variants[j];
+			var = env.variants[j];
 			else if (env.variants[j] == TR_DIRECT)
 				env.variants[j] = var;
 			if (env.variants[j] != var) {
@@ -699,9 +693,14 @@ static ir_graph_state_t do_tailrec(ir_graph *irg)
 	return 0;
 }
 
+
+/*
+ * This tail recursion optimization works best
+ * if the Returns are normalized.
+ */
 static optdesc_t opt_tailrec = {
 	"tail-recursion",
-	IR_GRAPH_STATE_NO_BADS | IR_GRAPH_STATE_CONSISTENT_OUTS,
+	IR_GRAPH_STATE_MANY_RETURNS | IR_GRAPH_STATE_NO_BADS | IR_GRAPH_STATE_CONSISTENT_OUTS,
 	do_tailrec,
 };