[fpc-devel] x86_64 question
J. Gareth Moreton
gareth at moreton-family.com
Thu Oct 1 19:17:47 CEST 2020
I have a small question with assembler size optimisation that maybe one
of you guys can give me a second opinion on:
If you are using the "test" instruction to test some of the lower bits
of an instruction, e.g. TEST RCX, $2, is there a penalty with calling
TEST CL, $2 instead? The instruction size is a lot smaller on account of
the immediate only being 1 byte long instead of 4 bytes, and are
mathematically equivalent. I know you have to be careful with partial
write penalties, but partial reads seem to be a bit more nebulous (the
register is not modified with TEST).
Gareth aka. Kit
This email has been checked for viruses by Avast antivirus software.
More information about the fpc-devel