[OpenMP] Replace GPU globalization calls with shared memory in the middle-end

[jhuber6]

Summary

The changes introduced in D97680 create a simpler interface to code that needs to be globalized. This interface is used to simplify the globalization calls in the middle end. We can check any globalization call that is only called by a single thread in the team and replace it with a static shared memory buffer.

[jdoerfert]

some initial comments.

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

991

994

No cast needed

999

prefer early exit, if (!...) return false;

1002

No need for it to be a constant

1006

Don't assume an order. Check all users, one should be a free, others can be whatever. If you find bitcast users, remember the type, if they all agree, use that for the alloca.

1708

no need to go over the free calls. they need to be users of the alloc and we remove them with the alloc.

1715

No need, use *CI below.

[jdoerfert]

We can reuse Attributor HeapToStack for this :)

[jhuber6]

Changing this optimization to replace the globalization calls with shared memory. Removing them will be done by the attributor using HeapToStack once we add the allocation calls and improve the attributor.

[jdoerfert]

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

68

I don't think we need this after all.

1010

For now, check isKernel(F) and only do this for kernel functions. Later we can be more aggressive but for now that should limit it properly, also with regards to the lifetime of those allocations.

1068

You cannot recollect while looping.
Move the recollect for free after the loop, delete the other one. Return true from this function when it deleted the use, that will update the alloc use list.

1072

return true;

[jhuber6]

Changing the test to simply check if we are in a non-SPMD kernel function. A more advanced approach can be used in the future.

[jdoerfert]

LGTM, one nit.

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

1031

Can you use a enum here or variable instead of "3".

[jhuber6]

Making changes.

[jhuber6]

Adding enum for address space constant.