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Re: 2.95, x86: severe performance problems with short arithmetic
- To: zack@bitmover.com
- Subject: Re: 2.95, x86: severe performance problems with short arithmetic
- From: John Wehle <john@feith.com>
- Date: Tue, 10 Aug 1999 16:38:09 -0400 (EDT)
- Cc: gcc@gcc.gnu.org
>> 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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