Broken ghc-7.0.3/vector combination?

Daniel Fischer at
Wed Apr 20 17:02:50 CEST 2011

Investigating the appearance of NaN in criterion's output, I found that 
NaNs were frequently introduced into the resample vectors when the 
resamples were sorted.

Further investigation of the sorting code in vector-algorithms revealed no 
bugs there, and if the runtime was forced to keep a keen eye on the 
indices, by replacing unsafeRead/Write/Swap with their bounds-checked 
counterparts or by 'trace'ing enough of their uses, the NaNs did not 

I could not reproduce the behaviour with ghc-7.0.1 (using exactly the same 
versions of the involved libraries), ghc-7.0.2 (different criterion 
release, the other libraries identical) or unoptimised compilation with 
7.0.3 (no NaNs encountered in some 100+ testruns with varying input).

So, is it possible that some change in ghc-7.0.3 vs. the previous versions 
caused a bad interaction between ghc-optimisations and vector fusion 
resulting in bad vector reads/writes?

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