Rosetta runs AVX2, FMA, BMI1/2, F16C and MOVBE, but, unlike an Intel
host, it has neither RDSEED, CLWB nor RDPID. --to-rosetta converts
everything --to-intel does and lowers these three as well:
- RDSEED becomes RDRAND (the /6 form of the same opcode), which also
returns a random value and sets CF.
- CLWB only writes a cache line back, so it becomes a NOP of the same
length.
- RDPID becomes a load of 0 through an optional stub: Rosetta's TSC_AUX
is a constant, not a processor index, so every thread reports
processor 0. A site with no movable instruction after it for the jump
is kept.
The flag implies --to-intel and conflicts with --windows. It is
independent of --macos: it only changes what the conversion produces, so
--macos alone leaves these instructions as they are, as on an Intel Mac,
and a title for Rosetta is relinked with --macos --to-rosetta. Intel
output is unchanged: the target is a parameter of the converter, Intel by
default.
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