+RTS -xc stack trace sometimes reported twice

Not sure if really a bug but just wanted to show. If this is a bug I'm hoping to fix this myself but I may need some guidance.

Stack trace reported by +RTS -xc is sometimes printed twice. This program reports it only once, as expected:

f :: Int -> Int
f = error "hello"

main = print (f 20)

➜  ghc_patch  ./error +RTS -xc                                                              
*** Exception (reporting due to +RTS -xc): (THUNK_1_0), stack trace: 
  Main.f,
  called from Main.CAF
  --> evaluated by: Main.main,
  called from Main.CAF
error: hello

But if I change it to this:

f :: Int -> Int
f x =
  let x = x + 20
  in x

main = print (f 20)

Stack trace is reported twice:

➜  ghc_patch  ./error +RTS -xc                                                              
*** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: 
  Main.f.x,
  called from Main.f,
  called from Main.main,
  called from Main.CAF
*** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: 
  Main.f.x,
  called from Main.f,
  called from Main.main,
  called from Main.CAF
error: <<loop>>

Can anyone confirm that this is really a bug?

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	simonmar
Operating system
Architecture

evaluated by: Main.main,\r\n called from Main.CAF\r\nerror: hello\r\n}}}\r\n\r\nBut if I change it to this:\r\n\r\n{{{#!haskell\r\nf :: Int -> Int\r\nf x =\r\n let x = x + 20\r\n in x\r\n\r\nmain = print (f 20)\r\n}}}\r\n\r\nStack trace is reported twice:\r\n\r\n{{{\r\n➜ ghc_patch ./error +RTS -xc \r\n*** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: \r\n Main.f.x,\r\n called from Main.f,\r\n called from Main.main,\r\n called from Main.CAF\r\n*** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: \r\n Main.f.x,\r\n called from Main.f,\r\n called from Main.main,\r\n called from Main.CAF\r\nerror: <>\r\n}}}\r\n\r\nCan anyone confirm that this is really a bug?","type_of_failure":"OtherFailure","blocking":[]} -->

changed weight to 3

added RTS Tbug Trac import labels

changed weight to 5

Some duplicates stack traces in this output as well, with a profiled ghc: http://lpaste.net/1842576927450202112.

Trac metadata

Trac field	Value
Priority	low → normal
Component	Runtime System → Profiling

added profiling label and removed RTS label

closed

I'm closing this ticket as it's not possible to reproduce anymore. Same program now prints this with -O:

*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace: 
  Main.f,
  called from Main.main,
  called from Main.CAF
  --> evaluated by: Main.main,
  called from Main.CAF
  --> evaluated by: Main.main
Main: test
CallStack (from HasCallStack):
  error, called at Main.hs:2:5 in main:Main
CallStack (from -prof):
  Main.f (Main.hs:2:1-16)
  Main.main (Main.hs:4:1-19)
  Main.CAF (<entire-module>)

and this without -O:

*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace: 
  Main.f,
  called from Main.CAF
  --> evaluated by: Main.main,
  called from Main.CAF
Main: test
CallStack (from HasCallStack):
  error, called at Main.hs:2:5 in main:Main
CallStack (from -prof):
  Main.f (Main.hs:2:1-16)
  Main.CAF (<entire-module>)

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedInvalid

added RTS label

added incorrect runtime result label

added Pnormal label