Re: [Xen-devel] [PATCH] x86/string: Use compiler builtins whenever possible

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/08/16 15:01, Jan Beulich wrote:
>>>> On 09.08.16 at 14:41, <andrew.cooper3@xxxxxxxxxx> wrote:
>> The use of -fno-builtin inhibits this automatic transformation.  Manually
>> tranform the callsites.  This causes constructs such as strlen("literal") to
>> be evaluated at compile time, and certain simple operations to be replaced
>> with repeated string operations.
> Iirc this was specifically avoided in at least older Linux because of
> compiler issues. Are you reasonably certain that those issues
> predate gcc 4.1.x (and don't exist at all in clang)? Other than that
> I'm of course fine with this patch.

Do you have any reference to these issues?  I cant find any reference.

I notice that Linux doesn't use these builtins, even today, but does
have arch specific implementations which are more efficient than our
common ones.  Still, it doesn't appear to be able to do any compile-time
evaluation.

~Andrew

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