jdoerfert marked an inline comment as done.
jdoerfert added inline comments.
================
Comment at: llvm/lib/Frontend/OpenMPIRBuilder.cpp:228
+ getOrCreateThreadID(getOrCreateIdent(SrcLocStr))};
+ bool UseCancelBarrier = !ForceSimpleCall && CancellationBlock;
+ Value *Result = Builder.CreateCall(
----------------
ABataev wrote:
> jdoerfert wrote:
> > ABataev wrote:
> > > ABataev wrote:
> > > > ABataev wrote:
> > > > > jdoerfert wrote:
> > > > > > ABataev wrote:
> > > > > > > jdoerfert wrote:
> > > > > > > > ABataev wrote:
> > > > > > > > > jdoerfert wrote:
> > > > > > > > > > ABataev wrote:
> > > > > > > > > > > jdoerfert wrote:
> > > > > > > > > > > > ABataev wrote:
> > > > > > > > > > > > > jdoerfert wrote:
> > > > > > > > > > > > > > ABataev wrote:
> > > > > > > > > > > > > > > Maybe add an assert when the cancellation version
> > > > > > > > > > > > > > > is requested but the cancellation block is not
> > > > > > > > > > > > > > > set? Instead of the generating simple version of
> > > > > > > > > > > > > > > barrier.
> > > > > > > > > > > > > > The interface doesn't work that way as we do not
> > > > > > > > > > > > > > know here if the cancellation was requested except
> > > > > > > > > > > > > > if the block was set. That is basically the flag
> > > > > > > > > > > > > > (and I expect it to continue to be that way).
> > > > > > > > > > > > > Maybe instead of `ForceSimpleBarrier` add a flag
> > > > > > > > > > > > > `EmitCancelBarrier` and if it set to true, always
> > > > > > > > > > > > > emit cancel barrier, otherwise always emit simple
> > > > > > > > > > > > > barrier? And add an assertion for non-set
> > > > > > > > > > > > > cancellation block or even accept it as a parameter
> > > > > > > > > > > > > here.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Also, what if we have inner exception handling in the
> > > > > > > > > > > > > region? Will you handle the cleanup correctly in case
> > > > > > > > > > > > > of the cancelation barrier?
> > > > > > > > > > > > > Maybe instead of ForceSimpleBarrier add a flag
> > > > > > > > > > > > > EmitCancelBarrier and if it set to true, always emit
> > > > > > > > > > > > > cancel barrier, otherwise always emit simple barrier?
> > > > > > > > > > > > > And add an assertion for non-set cancellation block
> > > > > > > > > > > > > or even accept it as a parameter here.
> > > > > > > > > > > >
> > > > > > > > > > > > What is the difference in moving some of the boolean
> > > > > > > > > > > > logic to the caller? Also, we have test to verify we
> > > > > > > > > > > > get cancellation barriers if we need them, both unit
> > > > > > > > > > > > tests and clang lit tests.
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > > Also, what if we have inner exception handling in the
> > > > > > > > > > > > > region? Will you handle the cleanup correctly in case
> > > > > > > > > > > > > of the cancelation barrier?
> > > > > > > > > > > >
> > > > > > > > > > > > I think so. Right now through the code in clang that
> > > > > > > > > > > > does the set up of the cancellation block, later
> > > > > > > > > > > > through callbacks but we only need that for regions
> > > > > > > > > > > > where we actually go out of some scope, e.g., parallel.
> > > > > > > > > > > 1. I'm just thinking about future users of thus
> > > > > > > > > > > interface. It woild be good if we could provide safe
> > > > > > > > > > > interface for all the users, not only clang.
> > > > > > > > > > > 2. Exit out of the OpenMP region is not allowed. But you
> > > > > > > > > > > may have inner try...catch or just simple compound
> > > > > > > > > > > statement with local vars that require
> > > > > > > > > > > constructors/destructors. And the cancellation barrier
> > > > > > > > > > > may exit out of these regions. And you need to call all
> > > > > > > > > > > required destructors. You'd better to think about it now,
> > > > > > > > > > > not later.
> > > > > > > > > > > 2. [...] You'd better to think about it now, not later.
> > > > > > > > > >
> > > > > > > > > > First, I do think about it now and I hope this was not an
> > > > > > > > > > insinuation to suggest otherwise.
> > > > > > > > > >
> > > > > > > > > > > 1. I'm just thinking about future users of thus
> > > > > > > > > > > interface. It woild be good if we could provide safe
> > > > > > > > > > > interface for all the users, not only clang.
> > > > > > > > > > > 2. Exit out of the OpenMP region is not allowed. But you
> > > > > > > > > > > may have inner try...catch or just simple compound
> > > > > > > > > > > statement with local vars that require
> > > > > > > > > > > constructors/destructors. And the cancellation barrier
> > > > > > > > > > > may exit out of these regions. And you need to call all
> > > > > > > > > > > required destructors.
> > > > > > > > > >
> > > > > > > > > > Generally speaking, we shall not add features that we
> > > > > > > > > > cannot use or test with the assumption we will use them in
> > > > > > > > > > the future. This is suggested by the LLVM best practices.
> > > > > > > > > > If you have specific changes in mind that are testable and
> > > > > > > > > > better than what I suggested so far, please bring them
> > > > > > > > > > forward. You can also bring forward suggestions on how it
> > > > > > > > > > might look in the future but without a real use case now it
> > > > > > > > > > is not practical to block a review based on that, given
> > > > > > > > > > that we can change the interface once the time has come.
> > > > > > > > > >
> > > > > > > > > > I said before, we will need callbacks for destructors,
> > > > > > > > > > actual handling of cancellation blocks, and there are
> > > > > > > > > > various other features missing right now. Nevertheless, we
> > > > > > > > > > cannot build them into the current interface, or even try
> > > > > > > > > > to prepare for all of them, while keeping the patches small
> > > > > > > > > > and concise.
> > > > > > > > > It won't work for clang, I'm afraid. You need a list of
> > > > > > > > > desructors here. But clang uses recursive codegen and it is
> > > > > > > > > very hard to walk over the call tree and gather all required
> > > > > > > > > destructors into a list. At least, it will require
> > > > > > > > > significant rework in clang frontend.
> > > > > > > > > Instead of generating the branch to cancellation block in the
> > > > > > > > > builder, I would suggest to call a single callback function
> > > > > > > > > provided by the frontend, which will generate correct branch
> > > > > > > > > over a chain of the destructor blocks. In this case, you
> > > > > > > > > won't need this cancellation block at all. This is what I
> > > > > > > > > meant when said that you need to think about this problem
> > > > > > > > > right now. That current solution is not very suitable for the
> > > > > > > > > use in the frontend.
> > > > > > > > > It won't work for clang,
> > > > > > > >
> > > > > > > > It won't work in the future or it does not work now? If the
> > > > > > > > latter, do you have a mwe to show the problem?
> > > > > > > 1. Both.
> > > > > > > 2. What is mwe? Sure, will simple test tomorrow.
> > > > > > both what?
> > > > > > A simple test is what I wanted, thx.
> > > > > Both - it won't work now and in tbe future it is going to be very
> > > > > hard to adapt clang to this interface.
> > > > I mean, handling of the cleanups.
> > > As an example, you can take a look at the code in
> > > `clang/test/OpenMP/cancel_codegen_cleanup.cpp` test. It is very simple.
> > > The simplest version of the same code will something like this:
> > > ```
> > > struct Obj {
> > > int a;
> > > Obj();
> > > ~Obj();
> > > };
> > >
> > > void foo() {
> > > #pragma omp for
> > > for (int i=0; i<1000; i++) {
> > > if(i==100) {
> > > Obj obj;
> > > #pragma omp cancel for
> > > }
> > > }
> > > }
> > >
> > > ```
> > > The object `obj` won't be deleted correctly with your scheme.
> > How did you run/compare this to come to the conclusion it does not work?
> >
> > I run it with the OpenMPIRBuilder for barriers enabled (D69922 +
> > -fopenmp-enable-irbuilder) and without, here is the full diff:
> >
> > ```
> > -declare dso_local void @__kmpc_barrier(%struct.ident_t*, i32)
> > +declare void @__kmpc_barrier(%struct.ident_t*, i32)
> > ```
> >
> > I don't see what you mean by it doesn't work, looks fine to me.
> >
> >
> > ---
> >
> > The above notwithstanding, if you have examples that expose problems with
> > this patch, please let me know.
> Try this one:
>
> ```
> struct Obj {
> int a;
> Obj();
> ~Obj();
> };
>
> void foo() {
> #pragma omp parallel
> for (int i=0; i<1000; i++) {
> if(i==100) {
> Obj obj;
> #pragma omp cancel parallel
> #pragma omp barrier
> }
> }
> }
> ```
Same result, cancel semantic is unaffected. Are you trying these?
Repository:
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https://reviews.llvm.org/D69785
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