[llvm-dev] How to interpret Selection DAG error output

David Chisnall via llvm-dev llvm-dev at lists.llvm.org
Fri Feb 19 04:26:34 PST 2016

On 18 Feb 2016, at 18:43, Rail Shafigulin via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> As far as I can understand LLVM cannot select it because the pattern is not specified. Unfortunately for me, I can't understand how to interpret this output. Would anybody be able to help me out?

You’ve had a few answers already, but just to add one more:

SelectionDAG has a viewGraph family of methods, that will dump a .dot file and open it with GraphViz.  These can be run from the debugger and produce *much* more readable output.  When I’m debugging, I generally stick a breakpoint on the code that’s triggering this error and get the pretty picture to try to figure out what’s going on.  It’s a lot easier to understand for nontrivial examples.


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