On Mon, 7 Mar 2016, David Laight wrote: > From: Sedat Dilek > ... > > Did someone look at the next/follow-ups in this thread? > > For example: D6629 "x86: Emit LAHF/SAHF instead of PUSHF/POPF" [2]? > > LAHF and SAHF come with the following note: > > This instruction executes as described above in compatibility mode and legacy > mode. > It is valid in 64-bit mode only if CPUID.80000001H:ECX.LAHF-SAHF[bit 0] = 1. > > So I suspect they can't be used.
Of course, there are other ways to save a single flag value (such as setz). It's up to the compiler developers to decide what they think is best. Alan Stern
