How to track down a bad llvm optimization pass

David Nadlinger via digitalmars-d-ldc digitalmars-d-ldc at
Mon Jun 20 03:32:15 PDT 2016

On 19 Jun 2016, at 7:58, Joakim via digitalmars-d-ldc wrote:
> Anyone know if we're breaking some llvm assumptions here?

I'm not aware of any – if that is the case (which is quite likely), 
then it's of course a bug in our code gen.

What I'd be inclined to do is to have a manual look at the IR 
immediately before GVN and see whether there is anything fishy to spot 
there already. I might also use a debugger on GVN to see exactly why it 
thinks it can perform a certain replacement – the LLVM pass internals 
are usually fairly well documented, although GVN is of course 
algorithmically a bit cumbersome to trace.

  — David

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