Basically you have to do two things at a minimum. First, decide whether the bug crashes the compiler (or an LLVM pass), or if the compiler is miscompiling the program. Based on what type of bug it is, follow the instructions in the linked section to narrow down the bug so that the person who fixes it will be able to find the problem more easily.

Once you have a reduced test-case, email information about the bug to: llvmbugs@cs.uiuc.edu. This should include all of the information necessary to reproduce the problem, including where you got the LLVM tree from (if you're not working out of CVS).

Thanks for helping us make LLVM better!

To figure out which program is crashing (the front-end, gccas, or gccld), run the llvm-gcc command line as you were when the crash occurred, but add a -v option to the command line. The compiler will print out a bunch of stuff, and should end with telling you that one of cc1, gccas, or gccld crashed.

• If cc1 crashed, you found a problem with the front-end. Jump ahead to the section on front-end bugs.
• If gccas crashed, you found a bug in one of the passes in gccas.
• If gccld crashed, you found a bug in one of the passes in gccld.
• Otherwise, something really weird happened. Email the list with what you have at this point.

  gccas -debug-pass=Arguments < /dev/null -o - > /dev/null

... which will print a list of arguments, indicating the list of passes that gccas runs. Once you have the input file and the list of passes, go to the section on debugging bugs in LLVM passes.

  llvm-as < /dev/null > null.bc
  gccld -debug-pass=Arguments null.bc

... which will print a list of arguments, indicating the list of passes that gccld runs. Once you have the input files and the list of passes, go to the section on debugging bugs in LLVM passes.

  bugpoint <input files> <list of passes>

bugpoint will print a bunch of output as it reduces the test-case, but it should eventually print something like this:

  ...
  Emitted bytecode to 'bugpoint-reduced-simplified.bc'

  *** You can reproduce the problem with: opt bugpoint-reduced-simplified.bc -licm

Once you complete this, please send the LLVM bytecode file and the command line to reproduce the problem to the llvmbugs mailing list.

To debug a miscompilation, you should choose which program you wish to run the output through, e.g. C backend, the JIT, or LLC, and a selection of passes, one of which may be causing the error, and run, for example:

  bugpoint -run-cbe -mode=compile [... optimization passes ...] file-to-test.bc

To debug the JIT:

  bugpoint -run-jit -mode=codegen -output=[correct output file] [bytecodefile]

  bugpoint -run-llc -mode=codegen -output=[correct output file] [bytecodefile]

To reproduce the error that bugpoint found, it is sufficient to do the following:

1. Regenerate the shared object from the safe bytecode file:
   

     llvm-dis -c safe.bc -o safe.c
   
     gcc -shared safe.c -o safe.so
   

2. If debugging LLC, compile test bytecode native and link with the shared object:
   

     llc test.bc -o test.s -f
   
     gcc test.s safe.so -o test.llc
   
     ./test.llc [program options]
   

If debugging the JIT, load the shared object and supply the test bytecode:


  lli -load=safe.so test.bc [program options]