On December 7, 2016 6:27:56 PM GMT+01:00, Florian Weimer <f...@deneb.enyo.de>
wrote:
>* Alexander Monakov:
>
>> On Wed, 7 Dec 2016, Segher Boessenkool wrote:
>>> > For example, this might have impact on writing test for GCC:
>>> >
>>> > When I am writing a test with noinline + noclone then my
>>> > expectation is that no such propagation happens, because
>>> > otherwise a test might turn trivial...
>>>
>>> The usual ways to prevent that are to add some volatile, or an
>>> asm("" : "+g"(some_var)); etc.
>>
>> No, that doesn't sound right. As far as I can tell from looking
>> that the GCC testsuite, the prevailing way is actually the
>> noinline+noclone combo, not the per-argument asms or volatiles.
>
>Agreed, that's what I've been using in the past for glibc test cases.
>
>If that doesn't work, we'll need something else. Separate compilation
>of test cases just to thwart compiler optimizations is a significant
>burden, and will stop working once we have LTO anyway.
>
>What about making the function definitions weak? Would that be more
>reliable?
Adding attribute((used)) should do the trick. It introduces unknown callers
and thus without cloning disables IPA.
Richard.
