[PATCH] D49003: [Debugify] Export per-pass debug info loss statistics

[Greg Bedwell via Phabricator via llvm-commits]

gbedwell added a comment.

This is really nice.  I agree it will be really useful, albeit with a minor concern about false positives in the stats themselves due to DCE transforms like what we ran into in https://llvm.org/PR37942 .

On some of the codebases I've tried, the warnings can be a bit noisy (and makes attempting to do any form of automatic testcase reduction based on their presence very difficult).  For example, in my testing with this patch I can see that Dead Store Elimination is generating some missing values and locations in a few testcases.  In every one I've looked at so far, these numbers relate to eliminated dead stores :).  Similarly, we don't know how many of the large instcombine number in the above PDF is down to DCE and how much is down to genuine DI loss. We've seen cases of both, but I'm not sure of the ratio.  Maybe a compelling argument for taking some approach along the lines of the suggested one of attaching undef dbg.values during DCE?



================
Comment at: tools/opt/Debugify.cpp:402
+  if (EC) {
+    errs() << EC.message() << ", " << Path << '\n';
+    return;
----------------
prefix this with something like "could not open file: "?


https://reviews.llvm.org/D49003