[llvm-dev] LLVM Backend Issues

Krzysztof Parzyszek via llvm-dev llvm-dev at lists.llvm.org
Tue Jun 21 09:19:01 PDT 2016

On 6/21/2016 11:12 AM, Jeff E via llvm-dev wrote:
> Also - It would be great if someone could point me to a document that
> describes some of these error messages? For example what does t26 ..t4 mean?

The t.. are just identifiers of the DAG nodes. It used to print 
addresses, but they were long and would change every time.

The "cannot select" errors are not that hard to track down: compile the 
failing testcase with -debug-only=isel and you'll see all the steps 
being taken up to the moment of failure.  The last few messages will be 
something like "match failed at nnn".  In your build directory in 
lib/Target/<yourtarget> there will be a file <yourtarget>GenDAGISel.inc. 
  It contains the matching "script".  The numbers nnn are shown in 
comments in that file and correspond to the steps the matcher performs. 
You'll be able to see what exactly it's trying to match.


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