diff --git a/mach/proto/mcg/mcg.h b/mach/proto/mcg/mcg.h
index dc70028c9..07da36467 100644
--- a/mach/proto/mcg/mcg.h
+++ b/mach/proto/mcg/mcg.h
@@ -24,7 +24,7 @@
 #include "ir.h"
 #include "mcgg.h"
 #include "hop.h"
-#include "vreg.h"
+#include "reg.h"
 #include "basicblock.h"
 #include "procedure.h"
 
diff --git a/mach/proto/mcg/pass_splitcriticaledges.c b/mach/proto/mcg/pass_splitcriticaledges.c
index a7fa63ee9..9237be750 100644
--- a/mach/proto/mcg/pass_splitcriticaledges.c
+++ b/mach/proto/mcg/pass_splitcriticaledges.c
@@ -88,4 +88,3 @@ void pass_split_critical_edges(struct procedure* proc)
 
 /* vim: set sw=4 ts=4 expandtab : */
 
-
diff --git a/mach/proto/mcg/reg.c b/mach/proto/mcg/reg.c
new file mode 100644
index 000000000..c4cf71058
--- /dev/null
+++ b/mach/proto/mcg/reg.c
@@ -0,0 +1,32 @@
+#include "mcg.h"
+
+static int vreg_count = 1;
+
+struct vreg* new_vreg(void)
+{
+	struct vreg* vreg = calloc(1, sizeof *vreg);
+	vreg->id = vreg_count++;
+	return vreg;
+}
+
+struct hreg* new_hreg(struct burm_register_data* brd)
+{
+	struct hreg* hreg = calloc(1, sizeof *hreg);
+	hreg->name = brd->name;
+	hreg->attrs = brd->attrs;
+	hreg->is_stacked = false;
+	return hreg;
+}
+
+struct hreg* new_stacked_hreg(int offset, uint32_t attrs)
+{
+	struct hreg* hreg = calloc(1, sizeof *hreg);
+	hreg->name = aprintf("stacked_%d", offset);
+	hreg->attrs = attrs;
+	hreg->is_stacked = true;
+	hreg->offset = offset;
+	return hreg;
+}
+
+/* vim: set sw=4 ts=4 expandtab : */
+
diff --git a/mach/proto/mcg/reg.h b/mach/proto/mcg/reg.h
new file mode 100644
index 000000000..62bbb6900
--- /dev/null
+++ b/mach/proto/mcg/reg.h
@@ -0,0 +1,26 @@
+#ifndef REG_H
+#define REG_H
+
+#define WITH_ATTR(a) (1<<(a))
+
+struct hreg
+{
+	const char* name;
+	uint32_t attrs;
+	bool is_stacked;
+	int offset;
+};
+
+struct vreg
+{
+	int id;
+};
+
+extern struct vreg* new_vreg(void);
+
+extern struct hreg* new_hreg(struct burm_register_data* brd);
+extern struct hreg* new_stacked_hreg(int offset, uint32_t attrs);
+
+#endif
+
+/* vim: set sw=4 ts=4 expandtab : */
diff --git a/mach/proto/mcg/table b/mach/proto/mcg/table
index c333a6310..8ff3b2416 100644
--- a/mach/proto/mcg/table
+++ b/mach/proto/mcg/table
@@ -1,28 +1,28 @@
 REGISTERS
 
-	r0  any int ret;
-	r1  any int;
-	r2  any int;
-	r3  any int;
-	r4  any int;
-	r5  any int;
-	r6  any int;
-	r7  any int;
-	r8  any int;
-	r9  any int;
-	r10 any int;
-	r11 any int;
+	r0  bytes4 int ret;
+	r1  bytes4 int;
+	r2  bytes4 int;
+	r3  bytes4 int;
+	r4  bytes4 int;
+	r5  bytes4 int;
+	r6  bytes4 int;
+	r7  bytes4 int;
+	r8  bytes4 int;
+	r9  bytes4 int;
+	r10 bytes4 int;
+	r11 bytes4 int;
 
-	s0  any float;
-	s1  any float;
-	s2  any float;
-	s3  any float;
-	s4  any float;
-	s5  any float;
-	s6  any float;
-	s7  any float;
-	s8  any float;
-	s9  any float;
+	s0  bytes4 float;
+	s1  bytes4 float;
+	s2  bytes4 float;
+	s3  bytes4 float;
+	s4  bytes4 float;
+	s5  bytes4 float;
+	s6  bytes4 float;
+	s7  bytes4 float;
+	s8  bytes4 float;
+	s9  bytes4 float;
 
 	cc  cc;
 
diff --git a/mach/proto/mcg/vreg.c b/mach/proto/mcg/vreg.c
deleted file mode 100644
index 636475de7..000000000
--- a/mach/proto/mcg/vreg.c
+++ /dev/null
@@ -1,10 +0,0 @@
-#include "mcg.h"
-
-static int vreg_count = 1;
-
-struct vreg* new_vreg(void)
-{
-	struct vreg* vreg = calloc(1, sizeof *vreg);
-	vreg->id = vreg_count++;
-	return vreg;
-}
diff --git a/mach/proto/mcg/vreg.h b/mach/proto/mcg/vreg.h
deleted file mode 100644
index ef92fd224..000000000
--- a/mach/proto/mcg/vreg.h
+++ /dev/null
@@ -1,12 +0,0 @@
-#ifndef VREG_H
-#define VREG_H
-
-struct vreg
-{
-	int id;
-};
-
-extern struct vreg* new_vreg(void);
-
-#endif
-
diff --git a/util/mcgg/gram.y b/util/mcgg/gram.y
index 5dc23a8be..a7ba08d70 100644
--- a/util/mcgg/gram.y
+++ b/util/mcgg/gram.y
@@ -74,7 +74,7 @@ registers
 
 register
     : ID                              { $$ = makereg($1); }
-    | register ID                     { $$ = $1; addregclass($1, $2); }
+    | register ID                     { $$ = $1; addregattr($1, $2); }
     ;
 
 declarations
@@ -95,7 +95,7 @@ allocates
             $$ = $1;
             if ($$->allocate)
                 yyerror("pattern type is defined to already allocate a register");
-            $$->allocate = getregclass($4);
+            $$->allocate = getregattr($4);
         }
     ;
 
diff --git a/util/mcgg/iburg.c b/util/mcgg/iburg.c
index 3eb703bcf..b9ecd2cd2 100644
--- a/util/mcgg/iburg.c
+++ b/util/mcgg/iburg.c
@@ -29,11 +29,12 @@ static Rule rules;
 static int nrules;
 
 static SMAPOF(struct reg) registers;
-static SMAPOF(struct regclass) registerclasses;
+static SMAPOF(struct regattr) registerattrs;
 
 static void print(char* fmt, ...);
 static void ckreach(Nonterm p);
 static void registerterminals(void);
+static struct regattr* makeregattr(const char* id);
 static void emitclosure(Nonterm nts);
 static void emitcost(Tree t, const char* v);
 static void emitcostcalc(Rule r);
@@ -47,7 +48,7 @@ static void emitleaf(Term p, int ntnumber);
 static void emitnts(Rule rules, int nrules);
 static void emitpredicatedefinitions(Rule rules);
 static void emitrecord(char* pre, Rule r, int cost);
-static void emitregisterclasses();
+static void emitregisterattrs();
 static void emitregisters();
 static void emitrule(Nonterm nts);
 static void emitstate(Term terms, Nonterm start, int ntnumber);
@@ -125,6 +126,10 @@ int main(int argc, char* argv[])
 	registerterminals();
 
 	start = nonterm("stmt", true);
+	makeregattr("bytes1");
+	makeregattr("bytes2");
+	makeregattr("bytes4");
+	makeregattr("bytes8");
 
 	yyin = infp;
 	yyparse();
@@ -137,7 +142,7 @@ int main(int argc, char* argv[])
 			yyerror("can't reach non-terminal `%s'\n", p->name);
 	#endif
 
-	emitregisterclasses();
+	emitregisterattrs();
 	emitregisters();
 	emitdefs(nts, ntnumber);
 	emitstruct(nts, ntnumber);
@@ -194,7 +199,7 @@ struct entry
 		struct term t;
 		struct nonterm nt;
 		struct reg r;
-		struct regclass rc;
+		struct regattr rc;
 	} sym;
 	struct entry* link;
 } * table[211];
@@ -236,7 +241,7 @@ static void* install(const char* name)
 struct reg* makereg(const char* id)
 {
 	struct reg* p = smap_get(&registers, id);
-	static int number = 1;
+	static int number = 0;
 
 	if (p)
 		yyerror("redefinition of '%s'", id);
@@ -248,25 +253,34 @@ struct reg* makereg(const char* id)
 	return p;
 }
 
-void addregclass(struct reg* reg, const char* id)
+struct regattr* makeregattr(const char* id)
 {
-	struct regclass* p = smap_get(&registerclasses, id);
-	static int number = 1;
+	struct regattr* p = smap_get(&registerattrs, id);
+	static int number = 0;
 
-	if (!p)
-	{
-		p = calloc(1, sizeof(*p));
-		p->name = id;
-		p->number = number++;
-		smap_put(&registerclasses, id, p);
-	}
+	if (p)
+		yyerror("redefinition of '%s'", id);
+	p = calloc(1, sizeof(*p));
+	p->name = id;
+	p->number = number++;
+	smap_put(&registerattrs, id, p);
 
-	reg->classes |= 1<<(p->number);
+	return p;
 }
 
-struct regclass* getregclass(const char* id)
+void addregattr(struct reg* reg, const char* id)
 {
-	struct regclass* p = smap_get(&registerclasses, id);
+	struct regattr* p = smap_get(&registerattrs, id);
+
+	if (!p)
+		p = makeregattr(id);
+
+	reg->attrs |= 1<<(p->number);
+}
+
+struct regattr* getregattr(const char* id)
+{
+	struct regattr* p = smap_get(&registerattrs, id);
 	if (!p)
 		yyerror("'%s' is not the name of a register class", id);
 	return p;
@@ -318,9 +332,6 @@ Term term(const char* id, int esn)
 		    p->name, p->esn);
 	p->link = *q;
 	*q = p;
-
-	if (esn != -1)
-		print("enum { %s = %d };\n", id, esn);
 	return p;
 }
 
@@ -415,10 +426,6 @@ static void print(char* fmt, ...)
 					fprintf(outfp, "%x", va_arg(ap, uint32_t));
 					break;
 
-				case 'X':
-					fprintf(outfp, "0x%" PRIx64 "ULL", va_arg(ap, uint64_t));
-					break;
-
 				case 's':
 					fputs(va_arg(ap, char*), outfp);
 					break;
@@ -499,16 +506,15 @@ static void ckreach(Nonterm p)
 		reach(r->pattern);
 }
 
-static void emitregisterclasses(void)
+static void emitregisterattrs(void)
 {
 	int i;
 
 	print("const char* %Pregister_class_names[] = {\n");
-	print("%1NULL,\n"); /* register class id 0 is invalid */
-	for (i=0; i<registerclasses.count; i++)
+	for (i=0; i<registerattrs.count; i++)
 	{
-		struct regclass* rc = registerclasses.item[i].right;
-		assert(rc->number == (i+1));
+		struct regattr* rc = registerattrs.item[i].right;
+		assert(rc->number == i);
 
 		print("%1\"%s\",\n", rc->name);
 	}
@@ -520,14 +526,14 @@ static void emitregisters(void)
 	int i;
 
 	print("const struct %Pregister_data %Pregister_data[] = {\n");
-	print("%1{ 0 },\n"); /* register id 0 is invalid */
 	for (i=0; i<registers.count; i++)
 	{
 		struct reg* r = registers.item[i].right;
-		assert(r->number == (i+1));
+		assert(r->number == i);
 
-		print("%1{ \"%s\", %X },\n", r->name, r->classes);
+		print("%1{ \"%s\", 0x%x },\n", r->name, r->attrs);
 	}
+	print("%1{ NULL }\n");
 	print("};\n\n");
 }
 
@@ -1168,6 +1174,11 @@ static void emitterms(Term terms)
 	Term p;
 	int k;
 
+	print("enum {\n");
+	for (k = 0, p = terms; p; p = p->link)
+		print("%1%S = %d,\n", p, p->esn);
+	print("};\n\n");
+
 	print("static const char %Parity[] = {\n");
 	for (k = 0, p = terms; p; p = p->link)
 	{
diff --git a/util/mcgg/iburg.h b/util/mcgg/iburg.h
index 24700e5e4..60e51d7b4 100644
--- a/util/mcgg/iburg.h
+++ b/util/mcgg/iburg.h
@@ -47,18 +47,18 @@ struct reg
 {
 	const char* name;      /* register name */
 	int number;            /* identifying number */
-	uint64_t classes;      // bitfield of classes */
+	uint32_t attrs;        /* bitfield of register attributes */
 };
 
-struct regclass
+struct regattr
 {
 	const char* name;      /* class name */
 	int number;            /* identifying number */
 };
 
 extern struct reg* makereg(const char* name);
-extern void addregclass(struct reg* reg, const char* regclass);
-extern struct regclass* getregclass(const char* name);
+extern void addregattr(struct reg* reg, const char* regattr);
+extern struct regattr* getregattr(const char* name);
 
 struct term
 { /* terminals: */
@@ -82,7 +82,7 @@ struct nonterm
 	Rule chain;       /* chain rules w/non-terminal on rhs */
 	Nonterm link;     /* next terminal in number order */
 	bool is_fragment; /* these instructions are all fragments */
-	struct regclass* allocate; /* allocate this kind of register */
+	struct regattr* allocate; /* allocate this kind of register */
 };
 extern void* lookup(const char* name);
 extern Nonterm nonterm(const char* id, bool allocate);
diff --git a/util/mcgg/mcgg.h b/util/mcgg/mcgg.h
index a3ff0197b..65dc26f54 100644
--- a/util/mcgg/mcgg.h
+++ b/util/mcgg/mcgg.h
@@ -61,12 +61,20 @@ extern const struct burm_instruction_data burm_instruction_data[];
 struct burm_register_data
 {
     const char* name;
-    uint32_t classes;
+    uint32_t attrs;
 };
 
 extern const struct burm_register_data burm_register_data[];
 extern const char* burm_register_class_names[];
 
+enum
+{
+    REGATTR_BYTES1 = 0,
+    REGATTR_BYTES2,
+    REGATTR_BYTES4,
+    REGATTR_BYTES8
+};
+
 #endif
 
 /* vim: set sw=4 ts=4 expandtab : */