[GHC] #7411: Exceptions are optimized away in certain situations

[GHC]

#7411: Exceptions are optimized away in certain situations
-------------------------------------+-------------------------------------
        Reporter:  SimonHengel       |                Owner:  tdammers
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  7.6.1
      Resolution:                    |             Keywords:  seq, deepseq,
                                     |  evaluate, exceptions
Operating System:  Linux             |         Architecture:  x86_64
                                     |  (amd64)
 Type of failure:  Incorrect result  |            Test Case:
  at runtime                         |  simplCore/should_fail/T7411
      Blocked By:                    |             Blocking:
 Related Tickets:  #5129 #15225      |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by tdammers):

 New nofib results.

 - `nofib-gn-gnl`: GHC and boot libraries compiled with `-fno-state-hack`
 compiling nofib normally, vs. GHC compiled normally and boot libraries
 compiled with `-fno-state-hack` compiling nofib normally. This measures
 the effect of compiling GHC itself with `-fno-state-hack`.
 - `nofib-ns-nn`: GHC compiled normally compiling nofib normally vs. GHC
 compiled normally compiling nofib with `-fno-state-hack`. This measures
 the effect of the state hack on nofib when using a vanilla compiler.
 - `nofib-ns-nn-gnl`: GHC compiled normally with boot libraries compiled
 with `-fno-state-hack` compiling nofib normally vs. GHC compiled normally
 with boot libraries compiled with `-fno-state-hack` compiling nofib with
 `-fno-state-hack`. This measures the effect of the state hack on nofib
 when using a vanilla compiler with state-hack-free boot libraries.

 Key observations:

 - Differences are now much closer to what we expect, specifically, whether
 we compile GHC and / or boot libraries with or without the state hack does
 not significantly change nofib performance (< 1%).
 - Compiling GHC itself and boot libraries without the state hack makes
 nofib compilation slightly slower than compiling only boot libraries
 without the state hack (~4%).
 - Compiling nofib without the state hack makes compilation significantly
 faster (~25%) than compiling nofib with the state hack, regardless of how
 GHC itself and the boot libraries were compiled.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7411#comment:49>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler