ABataev added inline comments.
================
Comment at: llvm/lib/Frontend/OpenMPIRBuilder.cpp:228
+ getOrCreateThreadID(getOrCreateIdent(SrcLocStr))};
+ bool UseCancelBarrier = !ForceSimpleCall && CancellationBlock;
+ Value *Result = Builder.CreateCall(
----------------
jdoerfert wrote:
> 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?
There must be different code for _kmpc_cancel_barrier call and further
processing. Will try to check with your patch tomorrow.
Repository:
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