search for: nosynch

> Since the scope is “opaque” and target specific, can you elaborate what kind of generic optimization can be performed? Some optimizations that are related to a single thread could be done without needing to know the actual memory scope. For example, an atomic acquire can restrict reordering memory operations after it, but allow reordering of memory operations (except another atomic acquire)

...might communicate (synchronize) with another thread causing that other thread to delete the memory. For this reason, to use dereferenceable as we currently do, we also need to know that the function does not synchronize with any other threads. To solve this problem, like nofree, I propose to add a nosynch attribute (to indicate that a function does not use (non-relaxed) atomics or otherwise synchronize with any other threads (e.g., perform I/O or, as a practical matter, use volatile accesses). I've posted a patch for the nofree attribute (https://reviews.llvm.org/D49165). nosynch's implemen...

[+Richard] On 07/11/2018 08:29 AM, Sanjoy Das wrote: > I'm not sure if nosynch is sufficient. What if we had: > > void f(int& x) { > if (false) { > int r0 = x; > } > } > > // other thread > free(<pointer to x>); > > The source program is race free, but LLVM may speculate the read from > x (seeing that it is dereferenceabl...

...ayingwithpointers.com> wrote: > > Hi, > > [Sorry for chiming in so late.] > > I understand why a straightforward metadata scheme won't work here, > but have you considered an alternate scheme that works in the > following way: > > - We add a MD node called !nosynch that lists a set of "domains" a > certain memory operation does *not* synchronize with. > > - Memory operations with !nosynch synchronize with memory operations > without any !nosynch metadata (so dropping !nosynch is safe). I’m not sure, but isn’t the synchscope id (...

...06:43 PM, Richard Smith wrote: > On Wed, 11 Jul 2018 at 16:13, Hal Finkel via llvm-dev > <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > [+Richard] > > > On 07/11/2018 08:29 AM, Sanjoy Das wrote: > > I'm not sure if nosynch is sufficient.  What if we had: > > > > void f(int& x) { > >   if (false) { > >     int r0 = x; > >   } > > } > > > > // other thread > > free(<pointer to x>); > > > > The source...