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Summary

Here are two extracts from the same profiling report file:

 parseIntegral                             Trace.Internal                       src/Trace/Internal.hs:(101,56)-(104,61)                622     3871885   18.7   16.8    80.8   71.1   4084 3057274056
  eventParser                              Trace                                src/Trace.hs:(343,87)-(374,9)                          623     1930555    4.3    5.7    60.5   54.3    947 1027402080
   parseFieldKind                          Trace                                src/Trace.hs:(454,9)-(468,48)                          636     1936408    0.8    0.6     0.8    0.6    172 107905344

And

 eventParser                               Trace                                src/Trace.hs:(343,87)-(374,9)                          626           0    0.0    0.0     0.0    0.0      0         0
  fieldParsers                             Trace                                src/Trace.hs:347:51-128                                628          16    0.0    0.0     0.0    0.0      0     26880
   parseFieldKind                          Trace                                src/Trace.hs:(454,9)-(468,48)                          630          98    0.0    0.0     0.0    0.0      0      3472
    parseIntegral                          Trace.Internal                       src/Trace/Internal.hs:(101,56)-(104,61)                635          59    0.0    0.0     0.0    0.0      0         0

The 2nd one shows the stack in the expected order. parseIntegral is a simple routine that does not make any direct or indirect call to eventParser. The only way I can see it could end up running eventParser code is through a thunk, but the documentation[1] explicitly mentions this case as being handled. Upon forcing, the stack attached to the thunk should be restored and the current cost center should therefore change to the one that created the thunk, not the one forcing it.

[1] https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/profiling.html#rules-for-attributing-costs

Steps to reproduce

Compile with -prof and -fno-prof-auto, -fno-prof-cafs (this is done via stack though, so other options might be included by it).

Expected behavior

My understanding is that the first stack snippet should not exist in the profile report.

Environment

• GHC version used: 8.10.2

Optional:

• Operating System: Archlinux
• System Architecture: x86_64