[LLVMdev] Summer of code proposal: add directive to uniquely identify loops of interest

[Dmitry Mikushin]

Dear all,

I would like to propose an average technical project that might have a
great use in many parts/derivatives of LLVM, including ours.

Consider you have dozens of regression tests in high-level languages,
reporting whether or not the recent changes in compiler are breaking some
kind of loop handling (vectorization, parallelization, etc.). Consider you
have a post-processing utility, which parses diagnostic output from each
test and tries to determine whether particular loop was handled properly.

In lower level, LLVM already has an infrastructure to test if a pass or a
backend transforms the given LLVM IR into expected form. Rather than that,
this proposal aims to address more high-level scope of use, where
developers need to verify the consistency of many parts of compiler
pipeline - from frontend to code generation. One natural solution might be
to markup loops in high-level language:

#pragma llvm loopname Loop1
for (int i = 0; i < n; i++)
{
    ...
}

and pass this name through the frontend to LLVM IR metadata node or
annotation intrinsic attached to the loop header.

In order to support multiple target languages (we are mostly interested in
C and Fortran), it is preferred to have GCC frontend support (maybe over
plugin and emitting to debug info, rather than to GIMPLE), and then - to
parse this additional info at DragonEgg level.

I'm not sure what is the situation with GSoC for LLVM this year. In any
case, we at KernelGen would like to support a student effort in
implementing this functionality and invite other groups to co-mentor the
process.

Dear students, should you have any questions - please do not hesitate to
contact me directly. You can also learn more about our work here [1].

[1]
https://hpcforge.org/plugins/mediawiki/wiki/kernelgen/index.php/Main_Page

--
Best regards,
- Dmitry Mikushin, on behalf of KernelGen team
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