[LLVMdev] Emitting IR in older formats (for NVVM)

[Jonathan Ragan-Kelley]

Thanks, all.




I didn’t realize a 7.0 RC was public and changed to 3.4—I will go down that road for now, though I’ll probably also look into integrating variants of the SPIR converter in the future.

Another possibility is to skip libnvvm altogether and use LLVM's NVPTX target.  This is of course harder since you have to configure the passes yourself instead of just calling a few C functions, but it does give you more control over the optimization pipeline and gives you full visibility into the compiler.  Unfortunately, there are some NVVM-specific optimizations missing upstream that we are not able to contribute back.


I appreciate the suggestion, but this is actually for a project which has been using NVPTX for years. The problem is that we see (dramatically) better performance from our OpenCL backend (via CL C source kernels) on NVIDIA hardware simply because kernels actually get optimized through the full NVCC-style stack. Based on related experience in other projects, I expect NVVM to provide a similar or greater bump over NVPTX. In short, I’d *love* to stick with NVPTX and the open source stack in LLVM trunk, but until it provides competitive performance on real programs (which, in my experience so far, it ~never does), it’s unfortunately not a strong alternative.
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