On Wed, Dec 07, 2016 at 04:12:48PM +0300, Alexander Monakov wrote: > [adding gcc@ for the compiler-testsuite-related discussion, please drop either > gcc@ or gcc-help@ from Cc: as appropriate in replies] > > 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. > > This behavior is new in gcc-7 due to new IPA-VRP functionality. So > -fno-ipa-vrp > gets the old behavior. I think from the testsuite perspective the situation > got > a bit worse due to this, as now in existing testcases stuff can get propagated > where the testcase used noinline+noclone to suppress propagation. This means > that some testcases may get weaker and no longer test what they were supposed > to. And writing new testcases gets less convenient too. > > However, this actually demonstrates how the noinline+noclone was not > future-proof, and in a way backfired now. Should there be, ideally, a single > 'noipa' attribute encompassing noinline, noclone, -fno-ipa-vrp, -fno-ipa-ra > and > all future transforms using inter-procedural knowledge?
Or just disable IPA-VRP into functions with noclone attribute, consider IPA-VRP as kind of virtual cloning. Jakub