Implement neg using OP_ADD

We have all the machinery in place to implement the neg instruction
as OP_ADD.  Doing that means we can ditch OP_NEG, and saves about
66 slice LUTs on the A7-100.

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

decode1.vhdl

@@ -243,7 +243,7 @@ architecture behaviour of decode1 is
 		2#0011101001#  =>       (MUL,    OP_MUL_L64,   RA,         RB,          NONE, RT,   '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '1', RC,   '0', '1'), -- mulld
 		2#0011101011#  =>       (MUL,    OP_MUL_L64,   RA,         RB,          NONE, RT,   '0', '1', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '1', '1', RC,   '0', '1'), -- mullw
 		2#0111011100#  =>       (ALU,    OP_AND,       NONE,       RB,          RS,   RA,   '0', '0', '0', '1', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- nand
-		2#0001101000#  =>       (ALU,    OP_NEG,       RA,         RB,          NONE, RT,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- neg
+		2#0001101000#  =>       (ALU,    OP_ADD,       RA,         NONE,        NONE, RT,   '0', '0', '1', '0', ONE,  '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- neg
 		2#0001111100#  =>       (ALU,    OP_OR,        NONE,       RB,          RS,   RA,   '0', '0', '0', '1', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- nor
 		2#0110111100#  =>       (ALU,    OP_OR,        NONE,       RB,          RS,   RA,   '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- or
 		2#0110011100#  =>       (ALU,    OP_OR,        NONE,       RB,          RS,   RA,   '0', '0', '1', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', RC,   '0', '0'), -- orc

decode_types.vhdl

@@ -13,7 +13,7 @@ package decode_types is
 		OP_LOAD, OP_STORE, OP_MADDHD, OP_MADDHDU, OP_MADDLD, OP_MCRF,
 		OP_MCRXR, OP_MCRXRX, OP_MFCR, OP_MFSPR, OP_MOD,
 		OP_MTCRF, OP_MTSPR, OP_MUL_L64,
-		OP_MUL_H64, OP_MUL_H32, OP_NEG, OP_OR,
+		OP_MUL_H64, OP_MUL_H32, OP_OR,
 		OP_POPCNTB, OP_POPCNTD, OP_POPCNTW, OP_PRTYD,
 		OP_PRTYW, OP_RLC, OP_RLCL, OP_RLCR, OP_SETB,
 		OP_SHL, OP_SHR,

execute1.vhdl

@@ -311,9 +311,6 @@ begin
                                         elsif std_match(e_in.insn(20 downto 11), "0100000000") then
                                                 ctrl_tmp.lr <= e_in.read_data3;
                                         end if;
-				when OP_NEG =>
-					result := ppc_neg(e_in.read_data1);
-					result_en := 1;
 				when OP_POPCNTB =>
 					result := ppc_popcntb(e_in.read_data3);
 					result_en := 1;