[U-Boot-Users] Re: what means this symbol "@"?
Charles.Wells at NielsenMedia.com
Mon May 12 15:05:29 CEST 2003
>I've never figured out why someone would want to use addi instead of ori in
>the second instruction of the load sequence.
The only authoritative explanation I've seen comes from IBM's
_The_PowerPC_Compiler_Writer's_Guide_; Steve Hoxey, et.al., 1/1996. Section
18.104.22.168 (p. 48-49) is entitled Loading a Constant into a Register. After
discussing the different techniques, they say:
"The add instructions are preferred to logical instructions because future
implementations may have a three-input adder, which permits executing the
two instructions (and other forms of add-feeding-add) in parallel, even
are not independent."
If your hand-crafted assembly language is being used to optimize an inner
loop, then it may make a difference. If it's used in some one-time
initialization code, it doesn't matter.
BTW, the CWG is a wonderfully entertaining resource for folks that want to
better understand the PowerPC architecture. It's available at:
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