[GHC] #12227: regression: out of memory with -O2 -ddump-hi on a complex INLINE function

23 Jun 2016

      #12227: regression: out of memory with -O2 -ddump-hi on a complex INLINE function
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           Reporter:  j6carey        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
  (CodeGen)                          |
           Keywords:                 |  Operating System:  Linux
       Architecture:  x86_64         |   Type of failure:  None/Unknown
  (amd64)                            |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Summary:

 Unlike GHC 7.10.2, when GHC 8.0.1 tries to compile a certain complex
 INLINE function with -O2 -ddump-hi, it runs out of memory.  Dropping
 either -O2 or -ddump-hi enables successful compilation.

 Oddly enough, triggering the issue requires using the function argument
 indirectly through a variable bound by a "where" clause, even though it is
 obvious to a human reader that the indirection is trivial.

 (Even after simplifying the original code to work around the out of memory
 issue, that indirection greatly increases the size of the ".dump-hi" file.
 It might be that the "out of memory" would not happen if one had
 sufficient RAM.)

 Using INLINABLE instead of INLINE seems to result in a much smaller RHS
 being recorded for the function in question, and does not trigger the
 problem.  (Perhaps INLINABLE records a more optimized RHS than does
 INLINE, though that is not obvious to me from the GHC User's Guide.)

 The attached files contain a reduced version of the original code that
 still triggers the problem.  (Of course, the reduced version is rather
 artificial and pointless, other than to demonstrate the problem.)
 Probably someone with sufficient understanding could shrink the example
 further.

 Please note that I have worked around the issue, and so I am not blocked
 by this problem, at least not currently.

 Attachments:

 - crash.bash

 - Crash.hs

 Observed behavior:

 On 64-bit x86 Ubuntu 16.04 LTS, with the attached files in the current
 directory, GHC 7.10.2 succeeds:
 {{{
 $ ./crash.bash
 The Glorious Glasgow Haskell Compilation System, version 7.10.2
 [1 of 1] Compiling Crash            ( Crash.hs, Crash.o )
 }}}
 whereas GHC 8.0.1 runs out of memory (or wedges my system if I comment out
 both "ulimit" commands in the script):
 {{{
 $ ./crash.bash
 The Glorious Glasgow Haskell Compilation System, version 8.0.1
 [1 of 1] Compiling Crash            ( Crash.hs, Crash.o )
 ghc: out of memory
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12227
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