Prior to this commit, the emitter would unconditionally emit a 10-byte
instruction known as MOVABS when loading a 64-bit immediate to a
register.
0: 48 b8 ef be ad de 00 movabs rax,0xdeadbeef
7: 00 00 00
With this change, it will instead rely on the fact that on x64 writes to
32-bit registers are automatically zero extended to 64-bits, allowing
us to emit a 5 or 6-bytes instruction with the same effect for certain
immediates.
0: b8 ef be ad de mov eax,0xdeadbeef
Prior to this commit, the emitter would unconditionally emit a 10-byte
instruction known as MOVABS when loading a 64-bit immediate to a
register.
0: 48 b8 ef be ad de ff movabs rax,0xffffffffdeadbeef
7: ff ff ff
With this change, it will instead emit a 7-byte instruction when it is
possible to express the 64-bit immediate using a signed 32-bit value.
0: 48 c7 c0 ef be ad de mov rax,0xffffffffdeadbeef
There's no real requirement to make this const, and this should also
be decided by the calling code, considering we had places that would
simply cast away the const and carry on.
These are only used internally. This also allows us to eliminate some
symbols that get dumped into the exposed Gen namespace.
By extension this also hides the Write[X] functions from OpArg's public
interface. This is only used internally by XEmitter, so they shouldn't
be usable by anything else.
MerryMage
TilkaandGitHub
Sintendo
Lioncash
spycrab
degasus
hthh
Matt Mastracci
Pierre Bourdon
aroulin