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Previously the pattern to extract status flags from inline assembly blocks was to use setcc in the block to write the flag to a register. This was suboptimal in a few ways: - It would lead to code like: sete %cl; test %cl; jne, i.e. a flag would just be loaded into a register and then reloaded to a flag. - The setcc would force the block to use an additional register. - If the client code didn't care for the flag value then the setcc would be entirely pointless but could not be eliminated by the optimizer. A more modern inline asm construct (since gcc 6 and clang 9) allows for "flag output operands", where a C variable can be written directly from a flag. The optimizer can then use this to produce direct code where the flag does not take a trip through a register. In practice this makes each affected operation sequence shorter by five bytes of instructions. It's unlikely this has a measurable performance impact. Reviewed by: kib, markj, mjg Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D23869
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