[ ghc-Bugs-630807 ] -O2 generates wrong code

Bugs item #630807, was opened at 2002-10-30 00:12
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Category: Compiler
Group: 5.04.1
>Status: Closed
>Resolution: Fixed
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
>Assigned to: Simon Peyton Jones (simonpj)
Summary: -O2 generates wrong code

Initial Comment:
I have a program (the Bluespec compiler), where using
-O2 generates a program that loops (or at least is VERY
slow), whereas not using generates a working program.

I can't really give you the source code, but perhaps
you can contact me and we can see if we can work
something out.

  -- Lennart

lennart@xxxxxxxxxxxxxx


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>Comment By: Simon Marlow (simonmar)
Date: 2002-12-13 10:47

Message:
Logged In: YES 
user_id=48280

Fixed in rev. 1.140 of Simplify.lhs, fix will be in 5.04.3 (if we 
release it).

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Comment By: Nobody/Anonymous (nobody)
Date: 2002-10-30 18:31

Message:
Logged In: NO 

Further investigations show that the generated code is not
looping, it is indeed correct, but it's just been incredibly
pessimised.  On a smaller example the unoptmized code
finishes in 0.02s and the optmized code in 18s.
It seem that the complexity of the (very complicated)
algorithm has suddenly become exponential with -O2.

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Comment By: Nobody/Anonymous (nobody)
Date: 2002-10-30 00:14

Message:
Logged In: NO 

BTW, this bug is in 5.02 too.


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