Re: [PATCH GIT 0.6] make use of register variables & size_t

[Bodo Eggert <harvested.in.lkml@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

Matthias-Christian Ott <matthias.christian@xxxxxxxxxx> wrote:

> And if you think "register" variables are outdated, please remove the
> CONFIG_REGPARM option from the Kernel source.

Register variables are outdated because they hinder the compiler from
optimizing by taking away 1/7 of the usable registers on x86. Use six
register variables and you're back to a accumulator-machine.
Use -O2 or -Os instead, the compiler is smarter than you.

The regparm calling convention will change the
load value -> store value on stack -> call sequence into
load value -> call -> store if needed
Obviously the second form can be better optimized than the first one.
Therefore it's a gain instead of a loss.

If you really want to help the compiler, look for something like repeated
pointer dereference or access to global variables and cache them in block-
local variables (pointers, int and uint only, even for caching chars).
Beware of volatile variables, and don't forget to look at the assembler code.
-- 
The generation of random numbers is too important to be left to chance. 

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