diff --git a/mach/proto/mcg/ir.c b/mach/proto/mcg/ir.c
index c4755b275..d2b64b162 100644
--- a/mach/proto/mcg/ir.c
+++ b/mach/proto/mcg/ir.c
@@ -68,17 +68,18 @@ struct ir* new_localir(int offset)
 
 struct ir* ir_walk(struct ir* ir, ir_walker_t* cb, void* user)
 {
+    assert(ir->root);
     if (cb(ir, user))
         return ir;
 
-    if (ir->left && !ir->left->is_root)
+    if (ir->left && (ir->left->root == ir->root))
     {
         struct ir* irr = ir_walk(ir->left, cb, user);
         if (irr)
             return irr;
     }
 
-    if (ir->right && !ir->right->is_root)
+    if (ir->right && (ir->right->root == ir->root))
     {
         struct ir* irr = ir_walk(ir->right, cb, user);
         if (irr)
@@ -106,7 +107,7 @@ static void print_expr(char k, const struct ir* ir)
     tracef(k, "%s", ir_data[ir->opcode].name);
     if (ir->size)
         tracef(k, "%d", ir->size);
-    tracef(k, "(");
+    tracef(k, ":%d(", ir->id);
 
 	switch (ir->opcode)
 	{
@@ -123,10 +124,23 @@ static void print_expr(char k, const struct ir* ir)
 			tracef(k, "%s", ir->u.bvalue->name);
 			break;
 
+        case IR_PHI:
+        {
+            int i;
+
+            for (i=0; i<ir->u.phivalue.count; i++)
+            {
+                if (i > 0)
+                    tracef(k, ", ");
+                tracef(k, "$%d", ir->u.phivalue.item[i]->id);
+            }
+            break;
+        }
+
 		default:
             if (ir->left)
             {
-                if (ir->left->is_root)
+                if (ir->left->root == ir->root)
                     tracef(k, "$%d", ir->left->id);
                 else
                     print_expr(k, ir->left);
@@ -134,7 +148,7 @@ static void print_expr(char k, const struct ir* ir)
             if (ir->right)
             {
                 tracef(k, ", ");
-                if (ir->right->is_root)
+                if (ir->right->root == ir->root)
                     tracef(k, "$%d", ir->right->id);
                 else
                     print_expr(k, ir->right);
diff --git a/mach/proto/mcg/ir.h b/mach/proto/mcg/ir.h
index abf4a1792..dc66ff757 100644
--- a/mach/proto/mcg/ir.h
+++ b/mach/proto/mcg/ir.h
@@ -10,21 +10,20 @@ struct ir
 	int size;
 	struct ir* left;
 	struct ir* right;
+	struct ir* root;
 	union
 	{
 		arith ivalue;
 		int rvalue;
 		const char* lvalue;
 		struct basicblock* bvalue;
+		ARRAYOF(struct ir) phivalue;
 	} u;
 
 	void* state_label; /* used by the iburg instruction selector */
 	int insn_no;       /* the table rule number for this instruction */
 	int goal_no;       /* the semantic type of this instruction; not stmt */
 	ARRAYOF(struct hop) hops; /* only for root IRs */
-
-	bool is_root : 1;
-	bool is_generated : 1;
 };
 
 extern const char* ir_names[];
diff --git a/mach/proto/mcg/mcg.h b/mach/proto/mcg/mcg.h
index ddd33aecf..3db29b86c 100644
--- a/mach/proto/mcg/mcg.h
+++ b/mach/proto/mcg/mcg.h
@@ -125,6 +125,7 @@ extern void pass_remove_dead_blocks(struct procedure* proc);
 extern void pass_eliminate_trivial_blocks(struct procedure* proc);
 extern void pass_instruction_selector(struct procedure* proc);
 extern void pass_promote_float_ops(struct procedure* proc);
+extern void pass_group_irs(struct procedure* proc);
 
 extern void procedure_compile(struct procedure* proc);
 
diff --git a/mach/proto/mcg/mcgg_generated_header.h b/mach/proto/mcg/mcgg_generated_header.h
index b37fe8cd3..eead127f1 100644
--- a/mach/proto/mcg/mcgg_generated_header.h
+++ b/mach/proto/mcg/mcgg_generated_header.h
@@ -4,20 +4,13 @@
 
 #define PANIC printf
 
-static int OP_LABEL(struct ir* ir)
-{
-	if (ir->is_root && ir->is_generated)
-	{
-		return ir_to_esn(IR_REG, ir->size);
-	}
-	return ir_to_esn(ir->opcode, ir->size);
-}
-
+#define OP_LABEL(p) burm_calculate_label(p)
 #define LEFT_CHILD(p) ((p)->left)
 #define RIGHT_CHILD(p) ((p)->right)
 	 
 #define burm_assert(b, s) assert(b)
 
+extern int burm_calculate_label(struct ir* ir);
 extern void burm_panic_cannot_match(struct ir* ir);
 
 static bool burm_predicate_int(struct ir* ir)
diff --git a/mach/proto/mcg/pass_convertstackops.c b/mach/proto/mcg/pass_convertstackops.c
index 285ca1626..c34eddf16 100644
--- a/mach/proto/mcg/pass_convertstackops.c
+++ b/mach/proto/mcg/pass_convertstackops.c
@@ -112,22 +112,20 @@ static void convert_block(struct procedure* proc, struct basicblock* bb)
         for (i=0; i<pushes.count; i++)
         {
             struct ir* ir = pushes.item[i];
-            assert(ir->is_root);
             *ir = *ir->left;
-            ir->is_root = true;
         }
 
         for (i=0; i<pops.count; i++)
         {
             struct ir* ir = pops.item[i];
-            struct ir* pushir = pushes.item[0];
-            struct ir* phi = new_ir1(IR_PHI, ir->size, pushir);
+            struct ir* phi = new_ir0(IR_PHI, ir->size);
 
-            for (j=1; j<pushes.count; j++)
-                phi = new_ir2(IR_PHI, ir->size, phi, pushes.item[j]);
+            for (j=0; j<pushes.count; j++)
+                array_appendu(&phi->u.phivalue, pushes.item[j]);
+            phi->root = phi;
 
-            phi->is_root = ir->is_root;
             *ir = *phi;
+            array_insert(&bb->irs, ir, 0);
         }
     }
 }
diff --git a/mach/proto/mcg/pass_groupirs.c b/mach/proto/mcg/pass_groupirs.c
new file mode 100644
index 000000000..833809b1d
--- /dev/null
+++ b/mach/proto/mcg/pass_groupirs.c
@@ -0,0 +1,95 @@
+#include "mcg.h"
+
+static ARRAYOF(struct ir) allirs;
+static ARRAYOF(struct ir) rootirs;
+
+static void addall(struct ir* ir)
+{
+    if (array_appendu(&allirs, ir))
+        return;
+
+    if (ir->left)
+        addall(ir->left);
+    if (ir->right)
+        addall(ir->right);
+}
+
+static void collect_irs(struct procedure* proc)
+{
+    int i;
+    
+    allirs.count = rootirs.count = 0;
+	for (i=0; i<proc->blocks.count; i++)
+    {
+        struct basicblock* bb = proc->blocks.item[i];
+        int j;
+
+        for (j=0; j<bb->irs.count; j++)
+		{
+			struct ir* ir = bb->irs.item[j];
+            addall(ir);
+			array_appendu(&rootirs, ir);
+		}
+    }
+}
+
+static void clear_roots(void)
+{
+	int i;
+
+	for (i=0; i<allirs.count; i++)
+	{
+		struct ir* ir = allirs.item[i];
+		ir->root = NULL;
+	}
+}
+
+static void find_roots(void)
+{
+	int i;
+
+	for (i=0; i<rootirs.count; i++)
+	{
+		struct ir* ir = rootirs.item[i];
+		assert(!ir->root);
+		ir->root = ir;
+	}
+}
+
+static void recursively_mark_root(struct ir* node, struct ir* root)
+{
+	if (node != root)
+	{
+		if (node->root)
+			return;
+		node->root = root;
+	}
+
+	if (node->left)
+		recursively_mark_root(node->left, root);
+	if (node->right)
+		recursively_mark_root(node->right, root);
+}
+
+static void find_non_roots(void)
+{
+	int i;
+
+	for (i=0; i<rootirs.count; i++)
+	{
+		struct ir* ir = rootirs.item[i];
+		recursively_mark_root(ir, ir);
+	}
+}
+
+void pass_group_irs(struct procedure* proc)
+{
+	collect_irs(proc);
+	clear_roots();
+	find_roots();
+	find_non_roots();
+}
+
+/* vim: set sw=4 ts=4 expandtab : */
+
+
diff --git a/mach/proto/mcg/pass_instructionselection.c b/mach/proto/mcg/pass_instructionselection.c
index ea13ae52b..2cb070dde 100644
--- a/mach/proto/mcg/pass_instructionselection.c
+++ b/mach/proto/mcg/pass_instructionselection.c
@@ -2,6 +2,7 @@
 
 static struct basicblock* current_bb;
 static struct hop* current_hop;
+static struct ir* current_ir;
 
 static const struct burm_emitter_data emitter_data;
 
@@ -19,6 +20,13 @@ void burm_panic_cannot_match(struct ir* ir)
 	exit(1);
 }
 
+int burm_calculate_label(struct ir* ir)
+{
+    if (ir->root != current_ir)
+		return ir_to_esn(IR_REG, ir->size);
+	return ir_to_esn(ir->opcode, ir->size);
+}
+
 static void emit_reg(struct ir* ir, int goal)
 {
     hop_add_reg_insel(current_hop, ir, goal);
@@ -81,14 +89,12 @@ static void walk_instructions(struct ir* ir, int goal)
     for (i=0; nts[i]; i++)
         walk_instructions(children[i], nts[i]);
 
-    ir->is_generated = true;
     ir->insn_no = insn_no;
     if (goal != 1)
         ir->goal_no = goal;
 
-    tracef('I', "I: $%d %s goal %d selected %s %d: %s\n",
+    tracef('I', "I: $%d goal %d selected %s %d: %s\n",
         ir->id,
-        ir->is_root ? "S" : " ",
         ir->goal_no,
         insndata->is_fragment ? "fragment" : "instruction",
         insn_no,
@@ -114,15 +120,15 @@ static void select_instructions(void)
 	for (i=0; i<current_bb->irs.count; i++)
 	{
 		int insnno;
-		struct ir* ir = current_bb->irs.item[i];
-		burm_label(ir);
+		current_ir = current_bb->irs.item[i];
+		burm_label(current_ir);
 
-		insnno = burm_rule(ir->state_label, 1);
+		insnno = burm_rule(current_ir->state_label, 1);
 		if (!insnno)
-			burm_panic_cannot_match(ir);
+			burm_panic_cannot_match(current_ir);
 
-        ir_print('I', ir);
-		walk_instructions(ir, 1);
+        ir_print('I', current_ir);
+		walk_instructions(current_ir, 1);
 	}
 }
 
diff --git a/mach/proto/mcg/procedure.c b/mach/proto/mcg/procedure.c
index 300882eb9..dc11e0a43 100644
--- a/mach/proto/mcg/procedure.c
+++ b/mach/proto/mcg/procedure.c
@@ -26,6 +26,7 @@ void procedure_compile(struct procedure* proc)
 
 	print_blocks('1', proc);
 
+    pass_group_irs(proc);
     pass_eliminate_trivial_blocks(proc);
     pass_remove_dead_blocks(proc);
     pass_convert_stack_ops(proc);
diff --git a/mach/proto/mcg/treebuilder.c b/mach/proto/mcg/treebuilder.c
index 58f19bdc2..8835c0b46 100644
--- a/mach/proto/mcg/treebuilder.c
+++ b/mach/proto/mcg/treebuilder.c
@@ -1,6 +1,5 @@
 #include "mcg.h"
 
-static struct symbol* currentproc;
 static struct basicblock* current_bb;
 
 static int stackptr;
@@ -76,7 +75,6 @@ static struct ir* appendir(struct ir* ir)
     int i;
 
     assert(current_bb != NULL);
-    ir->is_root = true;
     array_append(&current_bb->irs, ir);
 
     ir_print('0', ir);
@@ -479,8 +477,7 @@ static void insn_ivalue(int opcode, arith value)
         case op_dup:
         {
             struct ir* v = pop(value);
-            if (!v->is_root)
-                appendir(v);
+            appendir(v);
             push(v);
             push(v);
             break;
diff --git a/modules/src/data/array.c b/modules/src/data/array.c
index 8943323cb..bfaaf8e84 100644
--- a/modules/src/data/array.c
+++ b/modules/src/data/array.c
@@ -1,11 +1,10 @@
 #include <stdlib.h>
 #include <stdbool.h>
+#include <string.h>
 #include "array.h"
 
-void array_append(void* arrayp, void* value)
+static void extend(struct array* array)
 {
-    struct array* array = arrayp;
-
 	if (array->count == array->max)
 	{
 		int newmax = (array->max == 0) ? 8 : (array->max * 2);
@@ -14,7 +13,13 @@ void array_append(void* arrayp, void* value)
 		array->max = newmax;
 		array->item = newarray;
 	}
+}
 
+void array_append(void* arrayp, void* value)
+{
+    struct array* array = arrayp;
+
+    extend(array);
     array->item[array->count] = value;
     array->count++;
 }
@@ -40,6 +45,17 @@ bool array_appendu(void* arrayp, void* value)
     return false;
 }
 
+void array_insert(void* arrayp, void* value, int before)
+{
+    struct array* array = arrayp;
+
+    extend(array);
+    memmove(&array->item[before+1], &array->item[before],
+        (array->count-before) * sizeof(*array));
+    array->item[before] = value;
+    array->count++;
+}
+
 void array_remove(void* arrayp, void* value)
 {
     struct array* array = arrayp;
diff --git a/modules/src/data/array.h b/modules/src/data/array.h
index 601873571..63951ff5d 100644
--- a/modules/src/data/array.h
+++ b/modules/src/data/array.h
@@ -19,6 +19,7 @@ struct array
 
 extern void array_append(void* array, void* value);
 extern bool array_appendu(void* array, void* value);
+extern void array_insert(void* array, void* value, int before);
 extern void array_remove(void* array, void* value);
 extern bool array_contains(void* array, void* value);