Stack overflow weirdness

Daniel Fischer at
Thu Jan 27 12:45:03 CET 2011

While tuning some code, the test programme suddenly started producing stack 
Reverting the code to a previous version did not revert that behaviour, 
code that previously produced a well-behaved binary now produced stack 
overflowing ones.
But only with ghc-7.0.1, not with ghc-6.12.3 and ghc-6.12.1, and when 
compiled with optimisations (both, -O and -O2) and without profiling.
A HEAD from October and a freshly darcs pulled HEAD displayed the same 
behaviour as 7.0.1.
At some point I tried compiling with -fno-strictness (+ -O or -O2) which 
again produced well-behaved albeit somewhat slower binaries.
An hour or so later, I again compile with -O2 without -fno-strictness to 
see whether the Core revealed something and, as suddenly as the stack 
overflows started, they disappeared, for the time being, I consistently get 
well-behaved binaries.

A run of an overflowing binary with -hT -K32M produced a triangular graph 
with > 10MB Blackhole allocation and > 30MB TSO allocation in the peak.

Obviously the behaviour is not reproducible, nevertheless, perhaps somebody 
has an idea what went on. Or should I attribute it to cosmic rays?


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