#2722: <<loop> when compiling with -O option with ghc-6.10.0.20081019
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Reporter: uwe | Owner: simonpj
Type: bug | Status: infoneeded
Priority: normal | Milestone: 7.0.3
Component: libraries (other) | Version: 7.0.1
Resolution: | Keywords: arrows
Testcase: tyepcheck/should_run/T2722 | Blockedby:
Difficulty: Unknown | Os: Linux
Blocking: | Architecture: x86_64 (amd64)
Failure: Runtime crash |
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Comment(by simonpj):
Harumph. It turns out that `-fno-enable-rewrite-rules` doesn't work.
This patch fixes it
{{{
* Make -fno-enable-rewrite-rules work properly
I'd failed to propagate the Opt_EnableRewriteRules flag properly,
which meant that -fno-enable-rewrite-rules didn't disable all
rewrites. This patch fixes it.
M ./compiler/simplCore/CoreMonad.lhs -4 +1
M ./compiler/simplCore/SimplCore.lhs -1 +1
M ./compiler/simplCore/SimplUtils.lhs -7 +13
M ./compiler/simplCore/Simplify.lhs -1 +2
}}}
Once that is done, T2722 works fine with `-O -fno-enable-rewrite-rules`,
and loops with plain `-O`. (You don't need to recompile the libraries to
see this effect.)
So it's definitely a rewrite rule. It seems to me very likely that it's a
similar bug to the one I tracked down at the beginning of this ticket.
It's probably not strictly a GHC bug, but still a bug in a RULE in a
library shipped with GHC is much the same from a customer point of view.
To help find it,
* `-ddump-rule-firings` will show which rules are firing
* `-ddump-rule-rewrites` will additionally show before and after
* You can comment out rules to disable them individually. (But some are
in libraries, so that will require you to recompile the library.)
Thanks for helping
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2722#comment:20>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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