#7360: Case-of-identical-alts optimisation fails abjectly
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.6.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonpj@…):
commit bacf7ca075498aed745f68448f7e2b8d15c39541
{{{
Author: Simon Peyton Jones <[email protected]>
Date: Mon Dec 24 13:25:12 2012 +0000
Make combine-identical-alternatives work again (Trac #7360)
Move the "combine indentical alternatives" transformation *before*
simplifying the alternatives. For example
case x of y
[] -> length y
(_:_) -> length y }
If we look *post* simplification, since 'y' is used in the
alterantives, the case binders *might* be (see the keep_occ_info test
in Simplify.simplAlt); and hence the combination of the two
alteranatives does not happen. But if we do it *pre* simplification
there is no problem.
This fixes Trac #7360.
compiler/simplCore/SimplUtils.lhs | 127
++++++++++++++++++++-----------------
1 files changed, 68 insertions(+), 59 deletions(-)
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7360#comment:5>
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