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Extend the fastops test to cover instructions that operate on 8-bit data. Support for 8-bit instructions was omitted from the original commit purely due to complications with BT not having a r/m8 variant. To keep the RFLAGS.CF behavior deterministic and not heavily biased to '0' or '1', continue using BT, but cast and load the to-be-tested value into a dedicated 32-bit constraint. Supporting 8-bit operations will allow using guest_test_fastops() as-is to provide full coverage for DIV and IDIV. For divide operations, covering all operand sizes _is_ interesting, because KVM needs provide exception fixup for each size (failure to handle a #DE could panic the host). Link: https://lore.kernel.org/all/aIF7ZhWZxlkcpm4y@google.com Link: https://lore.kernel.org/r/20250909202835.333554-3-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>