solcasm (evm-assembler)

Install it

npm i solcasm

solc --asm compatible assembler

1.- Write EVM assembly in the same format as solc --asm output

  mstore(0x40, 0x80)
  callvalue
  dup1
  iszero
  tag_1
  jumpi
  0x00
  dup1
  revert
tag_1:
  pop
  dataSize(sub_0)
  dup1
  dataOffset(sub_0)
  0x00
  codecopy
  0x00
  return
stop

sub_0: assembly {
      mstore(0x40, 0x80)
}

2.- Compile it

npx solcasm contract.evm contract.bin

output:

6080604052348015600f57600080fd5b50600580601d6000396000f3006080604052