diff --git a/mach/powerpc/mcg/table b/mach/powerpc/mcg/table
index 3be30c306..7023c08b6 100644
--- a/mach/powerpc/mcg/table
+++ b/mach/powerpc/mcg/table
@@ -617,12 +617,14 @@ PATTERNS
 		cost 4;
 
 	out:(int)reg = MOD.I(left:(int)reg, right:(int)reg)
+        with preserved(%left), preserved(%right)
 		emit "divw %out, %left, %right"
         emit "mullw %out, %out, %right"
         emit "subf %out, %out, %left"
 		cost 12;
 
 	out:(int)reg = MODU.I(left:(int)reg, right:(int)reg)
+        with preserved(%left), preserved(%right)
 		emit "divwu %out, %left, %right"
         emit "mullw %out, %out, %right"
         emit "subf %out, %out, %left"
diff --git a/mach/proto/mcg/hop.h b/mach/proto/mcg/hop.h
index 0cc5dc0b1..21c7e9293 100644
--- a/mach/proto/mcg/hop.h
+++ b/mach/proto/mcg/hop.h
@@ -31,6 +31,7 @@ struct insel
 struct constraint
 {
     uint32_t attrs;
+	bool preserved;
     struct vreg* equals_to;
 };
 
diff --git a/mach/proto/mcg/pass_instructionselection.c b/mach/proto/mcg/pass_instructionselection.c
index 2bf5e5b59..860dad02f 100644
--- a/mach/proto/mcg/pass_instructionselection.c
+++ b/mach/proto/mcg/pass_instructionselection.c
@@ -100,6 +100,16 @@ static void constrain_input_reg(int child, uint32_t attr)
     get_constraint(vreg)->attrs = attr;
 }
 
+static void constrain_input_reg_preserved(int child)
+{
+    struct vreg* vreg = find_vreg_of_child(child);
+    struct constraint* c;
+
+    assert(vreg);
+    array_appendu(&current_hop->throughs, vreg);
+    get_constraint(vreg)->preserved = true;
+}
+
 static uint32_t find_type_from_constraint(uint32_t attr)
 {
     /* Looks through the registers and finds a concrete register implementing
@@ -158,6 +168,7 @@ static const struct burm_emitter_data emitter_data =
     &emit_value,
     &emit_eoi,
     &constrain_input_reg,
+    &constrain_input_reg_preserved,
     &constrain_output_reg,
     &constrain_output_reg_equal_to,
 };
diff --git a/util/mcgg/gram.y b/util/mcgg/gram.y
index 99fdeda95..891030a10 100644
--- a/util/mcgg/gram.y
+++ b/util/mcgg/gram.y
@@ -38,6 +38,7 @@ extern int yylex(void);
 %term NOTEQUALS
 %term PATTERNS
 %term PREFERS
+%term PRESERVED
 %term REGISTERS
 %term WHEN
 %term WITH
@@ -170,6 +171,8 @@ constraint
                                           $$->type = CONSTRAINT_EQUALS; $$->left = $2; $$->right = $5; }
     | CORRUPTED '(' ID ')'              { $$ = calloc(1, sizeof(*$$));
                                           $$->type = CONSTRAINT_CORRUPTED_ATTR; $$->left = $3; }
+    | PRESERVED '(' '%' ID ')'          { $$ = calloc(1, sizeof(*$$));
+                                          $$->type = CONSTRAINT_PRESERVED; $$->left = $4; }
     ;
 
 qfragments
diff --git a/util/mcgg/iburg.c b/util/mcgg/iburg.c
index 55a24e717..23705c7d8 100644
--- a/util/mcgg/iburg.c
+++ b/util/mcgg/iburg.c
@@ -1199,6 +1199,28 @@ static void emit_output_constraints(Rule r)
 	}
 }
 
+static void emit_input_constraints(Rule r)
+{
+	int i;
+	for (i=0; i<r->constraints.count; i++)
+	{
+		int index;
+		struct constraint* c = r->constraints.item[i];
+
+		if (c->type == CONSTRAINT_PRESERVED)
+		{
+			if (strcmp(c->left, r->label) == 0)
+				yyerror("cannot preserve an output register!");
+
+			index = 0;
+			if (!find_child_index(r->pattern, c->left, &index, NULL))
+				label_not_found(r, c->left);
+
+			print("%1data->constrain_input_reg_preserved(%d);\n", index);
+		}
+	}
+}
+
 /* emitinsndata - emit the code generation data */
 static void emitinsndata(Rule rules)
 {
@@ -1234,6 +1256,7 @@ static void emitinsndata(Rule rules)
 		}
 		
 		emit_output_constraints(r);
+		emit_input_constraints(r);
 		
 		while (f)
 		{
diff --git a/util/mcgg/iburg.h b/util/mcgg/iburg.h
index 8ba4f5ab9..739641d4d 100644
--- a/util/mcgg/iburg.h
+++ b/util/mcgg/iburg.h
@@ -21,6 +21,7 @@ enum
 {
 	CONSTRAINT_EQUALS,
 	CONSTRAINT_CORRUPTED_ATTR,
+	CONSTRAINT_PRESERVED,
 };
 
 struct constraint
diff --git a/util/mcgg/mcgg.h b/util/mcgg/mcgg.h
index a068fa660..c0c930a27 100644
--- a/util/mcgg/mcgg.h
+++ b/util/mcgg/mcgg.h
@@ -45,6 +45,7 @@ struct burm_emitter_data
     void (*emit_value)(int child);
     void (*emit_eoi)(void);
     void (*constrain_input_reg)(int child, uint32_t attr);
+    void (*constrain_input_reg_preserved)(int child);
     void (*constrain_output_reg)(uint32_t attr);
     void (*constrain_output_reg_equal_to)(int child);
 };
diff --git a/util/mcgg/scan.l b/util/mcgg/scan.l
index 272dd2bf1..447a7d395 100644
--- a/util/mcgg/scan.l
+++ b/util/mcgg/scan.l
@@ -46,6 +46,7 @@ static int braces = 0;
 "fragment"                  return FRAGMENT;
 "named"                     return NAMED;
 "prefers"                   return PREFERS;
+"preserved"                 return PRESERVED;
 "when"                      return WHEN;
 "with"                      return WITH;
 "=="                        return EQUALS;