Re: [Xen-devel] [PATCH] x86: fix variable_test_bit() asmconstraints

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 14/3/08 13:59, "Samuel Thibault" <samuel.thibault@xxxxxxxxxxxxx> wrote:

>> Atomic ops imply a barrier (otherwise the compiler can defeat the
>> purpose of the atomic operation). The non-atomic ones don't need a
>> dummy operand, but one that precisely describes the place in memory
>> that changes.
> 
> Mmm, won't that unnecessarily make the compiler put code to compute that
> place?

x86 has enough fancy addressing modes that usually the compiler can emit the
effective address without pre-computing any part of it. It's not guaranteed
to do this, though, it's true.

 -- Keir



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