Pass runtime strings in the target's global address space

[maleadt]

Exception names and backtrace strings are emitted in the target's global address space, but the runtime declarations used Ptr{Cchar} and cast them to the default address space. For SPIR-V, that does not describe the cross-workgroup storage containing the strings.

Represent runtime string arguments with a placeholder resolved per compiler job. Keep Ptr{Cchar} as the default and derive SPIR-V's pointer type from the data layout's global address space, avoiding an address-space cast. Cover both typed and opaque LLVM pointers and translate the result through both SPIR-V back-ends.

[maleadt]

I don't particularly like the new interface though, so I'm also going to explore getting this out of LLVM.

[vchuravy]

I thought we had already tried to fix this before?

[vchuravy]

https://github.com/JuliaGPU/OpenCL.jl/pull/302/changes

We have globalstring_ptr!(builder, String(fmt); addrspace=AS.Constant)

Edit: Ah I see the issue, we are emitting in AS.Constant, but your intrinsics would like to see AS 0

[maleadt]

Edit: Ah I see the issue, we are emitting in AS.Constant, but your intrinsics would like to see AS 0

Yes. But in the latest version, I made it so that we respecialize the runtime functions on a different type, so they are really accepting AS1 now, i.e., what globalstring_ptr! produces.

[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.41%. Comparing base (19e9962) to head (62c0c7b).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rtlib.jl	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #920      +/-   ##
==========================================
+ Coverage   85.14%   85.41%   +0.27%     
==========================================
  Files          29       29              
  Lines        5566     5582      +16     
==========================================
+ Hits         4739     4768      +29     
+ Misses        827      814      -13     

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