[SYCL][CUDA][libclc] Clone functions rather than aliasing in remangler

[joeatodd]

The libclc remangler handles function overloads with e.g. long long long and int, ensuring consistency with OpenCL C primitives. Previously, this was achieved by creating a GlobalAlias for each of the various overloads. However, the NVPTX target does not work with function aliases. Normally, an optimization pass removes these aliases, but the present approach prevents compiling with DPC++ for CUDA with -O0.

This PR changes the behaviour of the remangler to emit function clones (a copy of the function with a different name). There is a risk that this bloats the compiled code, but optimization should remove unneeded clones, as it did with unneeded aliases.

There is an additional barrier to -O0 compilation for NVPTX relating to nvvm_reflect, addressed here: #5900

Note: this PR is best reviewed as separate commits. The first commit makes the (small) functional change. The second commit is simply renaming all 'Alias*' variables to 'Clone*'.

[mlychkov]

Is it possible to add a LIT test for libclc-remangler?

[joeatodd]

Is it possible to add a LIT test for libclc-remangler?

Yes, good idea. I'll start working on this, but perhaps it ought to be a separate PR?

[mlychkov]

Is it possible to add a LIT test for libclc-remangler?

Yes, good idea. I'll start working on this, but perhaps it ought to be a separate PR?

I'm ok with adding a LIT test in a separate patch. Thank you.

[joeatodd]

@bader ping - I rebased to retrigger broken CI but it dismissed approvals

[bader]

@bader ping - I rebased to retrigger broken CI but it dismissed approvals

Please, use GitHub UI to re-request review, otherwise, it's hard to find PRs where inputs are needed.

[joeatodd]

@bader ping - I rebased to retrigger broken CI but it dismissed approvals

Please, use GitHub UI to re-request review, otherwise, it's hard to find PRs where inputs are needed.

Apologies - I will do this in future 👍