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Re: Functions locality and instruction fetch

On Sun, Jan 27, 2013 at 05:14:24PM +0000, Sad Clouds wrote:
> The question that was bugging me is this: if in the source file I write
> functions in linear order:
> f1()
> f2()
> f3()
> ...
> f10()
> will GCC generate their binary code in the same linear order,
> clustering them together in memory addresses?
> I ran 'nm' on binary files and it seems the above holds true, at least
> for GCC, but I would be wrong...

I've seen object code where that isn't true.
I've sure some versions of gcc re-order stuff - especially for static

Why do you want functions adjacent?
- to reduce the number of active TLB ?
- NUMA systems copying physical pages into local memory
- avoid some long instruction sequences for long jumps (don't they have
  to be generated anyway - unless they are linker generated trampolines)?

Sun might have had NUMA systems.


David Laight:

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