Option -Zg: Masm-compatible Code Generation

Option -Zg: Masm-compatible Code Generation

Option -Zg makes JWasm try an exact copy of Masm's code generation, which results in the following changes:

• the default prologue for procedures will use
    add [e]sp, - localsize
  instead of
    sub [e]sp, localsize.
• the default epilogue for procedures will almost always prefer to generate opcode LEAVE if possible.
• expressions
    <reg> == 0 and <reg> != 0
  will generate code
    or <reg>,<reg>
  instead of
    cmp <reg>,0.
• if invoke must extend an argument's size from word to dword, register eax remains unchanged.
• the segment value of FAR externals will always be assumed unknown, no matter whether the external is defined inside or outside of a segment block. Thus those labels are excluded from "far call optimization".
• if indirect addressing uses 2 (32- or 64-bit) registers and no scaling factor is used and the second register isn't ESP/RSP, then the registers are swapped: the second becomes base and the first becomes index ( the registers in an expression are counted from left to right ). [ since v2.10, this is standard behavior ].