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Re: basic asm and memory clobbers

On 11/20/2015 04:20 PM, Segher Boessenkool wrote:
On Fri, Nov 20, 2015 at 02:05:01PM +0100, Richard Henderson wrote:
I'd be perfectly happy to deprecate and later completely remove basic asm
within functions.

Because IMO it's essentially useless.  It has no inputs, no outputs, and no
way to tell the compiler what machine state has been changed.  We can say
that "it clobbers everything", but that's not actually useful, and quite
difficult as you're finding out.

It seems to me that it would be better to remove the feature, forcing what
must be an extremely small number of users to audit and update to extended

Should  asm("bla");  then be an extended asm with no input, no outputs,
no (non-automatic) clobbers?  That would be the most straightforward and
logical semantics, but will it break user code?

I'm suggesting that we don't accept that at all inside a function. One must audit the source and make a conscious decision to write asm("bla" : ); instead.

Accepting basic asm outside of a function is perfectly ok, since that's just a mechanism by which one can inject complete assembly routines into a C translation unit.


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