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:
> > 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
}
}
}
```
Repository:
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https://reviews.llvm.org/D69785/new/
https://reviews.llvm.org/D69785
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