[GHC] #14214: Users guide lies about default optimization level

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[GHC] #14214: Users guide lies about default optimization level

GHC - devs mailing list
#14214: Users guide lies about default optimization level
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:  8.4.1
          Component:  Compiler       |           Version:  8.2.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Documentation
  Unknown/Multiple                   |  bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 #14208 points out that the users guide claims that the default
 optimization level is `-O0`. However this apparently isn't true. We should
 decide whether this should be the default and, if so, identify and fix the
 differences.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14214>
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Re: [GHC] #14214: Users guide lies about default optimization level

GHC - devs mailing list
#14214: Users guide lies about default optimization level
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by bgamari:

Old description:

> #14208 points out that the users guide claims that the default
> optimization level is `-O0`. However this apparently isn't true. We
> should decide whether this should be the default and, if so, identify and
> fix the differences.

New description:

 ticket:14208#comment:5 points out that the users guide claims that the
 default optimization level is `-O0`. However this apparently isn't true.
 We should decide whether this should be the default and, if so, identify
 and fix the differences.

--

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14214#comment:1>
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Re: [GHC] #14214: Users guide lies about default optimization level

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#14214: Users guide lies about default optimization level
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by harendra):

 There are a number of issues with the documentation of optimization
 options. I guess all those can be dealt with in this ticket.

 1) The inconsistency described above in the ticket description is in the
 "Flag Reference" chapter:

 {{{

 Flag    Description     Type    Reverse
 -O0     Disable optimisations (default) dynamic -O
 }}}

 2) I would also suggest that we have another column in the "6.6.15.
 Individual optimisations" section to indicate which optimization levels
 enable each option. It could be in the form "0, 1, 2". This will really
 help in quickly identifying the options applicable to a particular level.

 3) 6.3.1. -O*: convenient “packages” of optimisation flags. This section
 should perhaps mention what is the default?

 4) 6.3.1. -O*: convenient “packages” of optimisation flags. This section
 says: "The easiest way to see what -O (etc.) “really mean” is to run with
 -v, then stand back in amazement." But when I tried it "-v" did not tell
 me what options are enabled.

 5) Some flags are documented like this:
 {{{
 -fno-opt-coercion
 Default:        off
 Turn off the coercion optimiser.
 }}}

 This is confusing. It says "Default: off", the double negation would mean
 that "-fopt-coercion" is "on". Is that the case? Is there a "-fopt-
 coercion"? If yes, can we document that instead? If not, we can be more
 explicit about the double negation.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14214#comment:2>
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Re: [GHC] #14214: Users guide lies about default optimization level

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#14214: Users guide lies about default optimization level
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * owner:  (none) => bgamari


--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14214#comment:3>
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Re: [GHC] #14214: Users guide lies about default optimization level

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#14214: Users guide lies about default optimization level
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * cc: patrickdoc (added)


Comment:

 CCing patrickdoc, who has some great work on improving documentation in
 the past.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14214#comment:4>
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Re: [GHC] #14214: Users guide lies about default optimization level

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#14214: Users guide lies about default optimization level
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by bgamari):

 In response to comment:2:

 Regarding (2): It would be great to have the documentation specify
 precisely which flags each of the optimisation levels implies. However, I
 think we would ideally like to have these lists generated from the
 implementation; otherwise it's only a matter of time until they fall out-
 of-date.

 Regarding (3): I believe that as of
 b2b416014e4276ebb660d85c3a612f7ca45ade78 there is now such a mention.

 Regarding (4): Indeed, it looks like this has been out-of-date for quite a
 long time; I don't remember a time when `-v` told you anything about which
 optimisation flags were used.

 Regarding (5): I absolutely agree. The documentation for some of these
 flags is incredibly confusing. What makes things complicated is that
 `-fopt-coercion` doesn't currently exist.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14214#comment:5>
GHC <http://www.haskell.org/ghc/>
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Re: [GHC] #14214: Users guide lies about default optimization level

GHC - devs mailing list
In reply to this post by GHC - devs mailing list
#14214: Users guide lies about default optimization level
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4098
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * differential:   => Phab:D4098


Comment:

 See Phab:D4098 for a first cut.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14214#comment:6>
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