Re: [GHC] #1547: Arity can decrease with -prof
#1547: Arity can decrease with -prof ---+ Reporter: igloo | Owner: Type: bug| Status: new Priority: normal | Milestone: _|_ Component: Profiling |Version: 6.6.1 Severity: normal | Resolution: Keywords: | Difficulty: Unknown Testcase: stm package/tests/conc052 | Architecture: Unknown Os: Unknown| ---+ Changes (by simonmar): * priority: high = normal * milestone: 6.10 branch = _|_ Comment: bug isn't manifesting any more, and doesn't seem to be an urgent problem. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1547#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #1547: Arity can decrease with -prof
#1547: Arity can decrease with -prof ---+ Reporter: igloo | Owner: Type: bug| Status: new Priority: high | Milestone: 6.10 branch Component: Profiling |Version: 6.6.1 Severity: normal | Resolution: Keywords: | Difficulty: Unknown Testcase: stm package/tests/conc052 | Architecture: Unknown Os: Unknown| ---+ Comment (by simonmar): Update: conc052 is now apparently not failing any more, but this bug hasn't been fixed. I imagine something else has changed such that we don't tickle the bug any more. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1547#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #1547: Arity can decrease with -prof
#1547: Arity can decrease with -prof
---+
Reporter: igloo | Owner:
Type: bug| Status: new
Priority: high | Milestone: 6.10 branch
Component: Profiling |Version: 6.6.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: stm package/tests/conc052 | Architecture: Unknown
Os: Unknown|
---+
Comment (by simonpj):
I had a half-done change in `SimplUtils` which I'm just going to dump here
for now. The actual code change (which I am not sure is right) is this:
{{{
hunk ./compiler/simplCore/SimplUtils.lhs 827
- any isRuntimeVar bndrs
+ any isRuntimeVar bndrs || not (exprIsTrivial body)
+ -- Note [RHS eta expansion]
}}}
and the note is this:
{{{
Note [RHS eta expansion]
The basic idea is to transform
f = \x1..xn - N == f = \x1..xn y1..ym - N y1..ym
(n = 0)
where (in both cases)
* The xi can include type variables
* The yi are all value variables
* N is a NORMAL FORM (i.e. no redexes anywhere)
wanting a suitable number of extra args.
This is OK even if n=0; for example:
let g=\xs. x:xs in (\ys. map g ys)
Here we can eta expand to
\ys. let g=\xs. x:xs in map g ys
You might think the f-binding woudl have floated, but it may not when
we are profiling:
f = scc foo (let g=\xs. x:xs in (\xs. map g ys))
Furthermore, f's arity might have been 1 before, if it originally looked
like
h g ys = map g ys
f = scc foo (h (\xs. x:xs))
and we do not expect like the arity to decrease so that it now looks
like zero (to the cheap-and-cheerful exprArity).
However, we must be careful not to undo the effect of eta-reduction, hence
the check for `(not (exprIsTrivial body))`.
}}}
I just want to capture the state of play because I can't finish this
today.
Simon
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1547#comment:2
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler___
Glasgow-haskell-bugs mailing list
Glasgow-haskell-bugs@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #1547: Arity can decrease with -prof
#1547: Arity can decrease with -prof
---+
Reporter: igloo | Owner:
Type: bug| Status: new
Priority: high | Milestone: 6.10 branch
Component: Profiling |Version: 6.6.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: stm package/tests/conc052 | Architecture: Unknown
Os: Unknown|
---+
Changes (by simonpj):
* testcase: = stm package/tests/conc052
* summary: conc052 core lint errors in profc/profasm ways = Arity can
decrease with -prof
* milestone: 6.8 branch = 6.10 branch
Old description:
The conc052 test (in the stm package) on amd64/Linux is giving core lint
errors for the profc/profasm ways.
Part of #1546 might be the same problem.
New description:
Something like
{{{
f = \p\q.body
x = scc foo f (\y.e)
}}}
shows f having arity 2, and hence x having arity 1. But when we inline f,
we get
{{{
x = scc foo let p = \x.e in \q.body
}}}
and the cheap-and-cheerful arity discovery function (`exprArity`) detects
arity of 0, not 1. And then !CoreLint complains about the inconsistency
of arity and strictness info.
This is unpleasant but not actually a problem.
It shows up in the `conc052` test (in the stm package).
Part of #1546 might be the same problem.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1547#comment:1
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler___
Glasgow-haskell-bugs mailing list
Glasgow-haskell-bugs@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
