On 22 Aug 2018, at 18:45, Hans Wennborg <h...@chromium.org> wrote: > > On Wed, Aug 22, 2018 at 3:48 AM, Dimitry Andric <dimi...@andric.com> wrote: >> On 22 Aug 2018, at 05:58, Wei Mi <w...@google.com> wrote: >>> >>> On Fri, Aug 17, 2018 at 1:27 PM, Dimitry Andric <dimi...@andric.com> wrote: >>> On 16 Aug 2018, at 00:51, Joerg Sonnenberger via llvm-dev >>> <llvm-...@lists.llvm.org> wrote: >>>> On Tue, Aug 07, 2018 at 09:49:16PM +0200, Dimitry Andric via llvm-dev >>>> wrote: >>>>> This is a regression caused by https://reviews.llvm.org/rL323281: >>>>> >>>>> ------------------------------------------------------------------------ >>>>> r323281 | wmi | 2018-01-23 23:27:57 +0000 (Tue, 23 Jan 2018) | 12 lines >>>>> >>>>> Adjust MaxAtomicInlineWidth for i386/i486 targets. >>>>> >>>>> This is to fix the bug reported in >>>>> https://bugs.llvm.org/show_bug.cgi?id=34347#c6. >>>>> Currently, all MaxAtomicInlineWidth of x86-32 targets are set to 64. >>>>> However, >>>>> i386 doesn't support any cmpxchg related instructions. i486 only supports >>>>> cmpxchg. >>>>> So in this patch MaxAtomicInlineWidth is reset as follows: >>>>> For i386, the MaxAtomicInlineWidth should be 0 because no cmpxchg is >>>>> supported. >>>>> For i486, the MaxAtomicInlineWidth should be 32 because it supports >>>>> cmpxchg. >>>>> For others 32 bits x86 cpu, the MaxAtomicInlineWidth should be 64 because >>>>> of cmpxchg8b. >>>> >>>> This seems to be somewhat undesirable. Does *anyone* care about real >>>> i386 support at this point? NetBSD certainly doesn't and I think we are >>>> already the odd man for a number of cases like this. >>> >>> >>> Yes, and since this causes quite a number of regressions for us, I would >>> really prefer this revision to be reverted, at least in the 7.0.0 >>> branch. I have already reverted it locally in our FreeBSD project >>> branch for importing llvm/clang 7.0.0. Hans, what is your opinion about >>> this? >>> >>> -Dimitry >>> >>> >>> Sorry I missed the thread for quite a while. Dimitry, I am very confused >>> because you reported the issue in >>> https://bugs.llvm.org/show_bug.cgi?id=34347#c6, so you want r323281 to be >>> reverted and let llvm to generate cmxchg8b instruction for i486? >> >> Since it's been doing this for a number of years now, I don't think it would >> be bad at all, at least not for FreeBSD. At least, a lot more effort is >> needed to supply properly working atomic libcalls for 64 bit values on i386. >> (They can't be implemented without at least a bit of kernel assistance.) > > According to the release schedule we should tag RC2 today. Do you > think there's any chance of getting this figured out by today?
Since I'm testing on FreeBSD 11.x, and that will take quite a while to get any new changes, I'd say it's safer to revert for now, at least on the branch. At least then I can build and test the RCs on i386-freebsd. :) -Dimitry
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