core: Implement the addex instruction

The addex instruction is like adde but uses the XER[OV] bit for the
carry in and out rather than XER[CA].

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

decode1.vhdl

@@ -172,6 +172,7 @@ architecture behaviour of decode1 is
         2#1000001010#  =>       (ALU,    OP_ADD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', ZERO, '1', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- addco
         2#0010001010#  =>       (ALU,    OP_ADD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', CA,   '1', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- adde
         2#1010001010#  =>       (ALU,    OP_ADD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', CA,   '1', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- addeo
+        2#0010101010#  =>       (ALU,    OP_ADD,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', OV,   '1', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- addex
         2#0011101010#  =>       (ALU,    OP_ADD,       RA,         CONST_M1,    NONE, RT,   '0', '0', '0', '0', CA,   '1', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- addme
         2#1011101010#  =>       (ALU,    OP_ADD,       RA,         CONST_M1,    NONE, RT,   '0', '0', '0', '0', CA,   '1', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- addmeo
         2#0011001010#  =>       (ALU,    OP_ADD,       RA,         NONE,        NONE, RT,   '0', '0', '0', '0', CA,   '1', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- addze

decode_types.vhdl

@@ -26,7 +26,7 @@ package decode_types is
     type input_reg_c_t is (NONE, RS, RCR);
     type output_reg_a_t is (NONE, RT, RA, SPR);
     type rc_t is (NONE, ONE, RC);
-    type carry_in_t is (ZERO, CA, ONE);
+    type carry_in_t is (ZERO, CA, OV, ONE);
 
     constant SH_OFFSET : integer := 0;
     constant MB_OFFSET : integer := 1;

execute1.vhdl

@@ -164,6 +164,8 @@ architecture behaviour of execute1 is
 	    return '0';
 	when CA =>
 	    return xerc.ca;
+        when OV =>
+            return xerc.ov;
 	when ONE =>
 	    return '1';
 	end case;
@@ -594,7 +596,13 @@ begin
                 carry_64 := result_with_carry(64);
                 if e_in.insn_type = OP_ADD then
                     if e_in.output_carry = '1' then
-                        set_carry(v.e, carry_32, carry_64);
+                        if e_in.input_carry /= OV then
+                            set_carry(v.e, carry_32, carry_64);
+                        else
+                            v.e.xerc.ov := carry_64;
+                            v.e.xerc.ov32 := carry_32;
+                            v.e.write_xerc_enable := '1';
+                        end if;
                     end if;
                     if e_in.oe = '1' then
                         set_ov(v.e,