x86, hweight: Use a 32-bit popcnt for __arch_hweight32()

Use a 32-bit popcnt instruction for __arch_hweight32(), even on
x86-64.  Even though the input register will *usually* be
zero-extended due to the standard operation of the hardware, it isn't
necessarily so if the input value was the result of truncating a
64-bit operation.

Note: the POPCNT32 variant used on x86-64 has a technically
unnecessary REX prefix to make it five bytes long, the same as a CALL
instruction, therefore avoiding an unnecessary NOP.

Reported-by: Linus Torvalds <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
Cc: Borislav Petkov <[email protected]>
LKML-Reference: <[email protected]>

0 files changed, 0 insertions, 0 deletions