Investigate unused opcodes

[bettio]

None of our tests are generating code making use of the following opcodes:

X_OPCODE(OP_ALLOCATE_ZERO, 14, allocate_zero)
X_OPCODE(OP_KILL, 17, kill)
X_OPCODE(OP_PUT, 71, put)
X_OPCODE(OP_MAKE_FUN2, 103, make_fun2)
X_OPCODE(OP_BS_ADD, 111, bs_add)

Are they still in use? Should we remove them?

[petermm]

According to Amp they are safe to remove since AtomVM is otp26+

https://ampcode.com/threads/T-019d2531-b068-713f-bcc3-41a784564a1c

Retired BEAM Opcodes in AtomVM

All five opcodes are officially retired in Erlang/OTP's genop.tab (marked with -). The modern Erlang compiler has zero code paths that emit any of them.

Opcode	#	Replaced By	Since
allocate_zero	14	allocate + init_yregs	OTP 24
kill (actually init)	17	init_yregs	OTP 24
put	71	put_tuple2	OTP 22
make_fun2	103	make_fun3	OTP 24
bs_add	111	bs_create_bin	OTP 25

Safe to remove if AtomVM only targets .beam files compiled with OTP 25+. Note that OP_PUT already has no case implementation in opcodesswitch.h.

[pguyot]

allocate_zero and make_fun2 can be emitted by OTP26:

• Test allocate_zero opcode on OTP26 #2236
• Test make_fun2 opcode on OTP26 #2237

[pguyot]

bs_add can also be emitted by OTP26 and OTP27.

See #2245

[pguyot]

I wasn't able to emit kill, I think we can close this issue.