2.95, x86: severe performance problems with short arithmetic

[John Wehle]

>>   1) A 16 bit write to a register immediately followed by a 32 bit read
>>      of the register.  This will cause a stall.  Converting the 16 bit
>>      write to a 32 bit write avoids the stall, however this may cause a
>>      stall with an earlier instruction (if I recall correctly).
>
>Does this include something like this?
>
>	movzbw %dl, %ax
>	addl %eax, %esi
>

Probably ... I don't have the relevant Intel document handy at
the moment.  There are certain special cases (if I recall).  More
information is available in the Intel Optimization Manual which
should be available from http://developer.intel.com .

-- John
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