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Generated C code under -prof -fprof-auto -fprof-cafs very slow to compile

    • Open Issue created by orenbenkiki @trac-orenbenkiki

    Some background: This is C code generated when I turned on profiling with -fprof-auto -fprof-cafs, on Haskell code that contains a large amount of injected TemplateHaskell code. GHC takes several minutes to compile this on its side; but for some reason it emits the attached C code, which (if compiled with -O) takes "forever" to compile. At least, I killed it after consuming 3 hours of CPU and occupying 9GB of RAM.

    I also opened a GCC bug for this; but a cursory look seems to indicate this C code is trying to build a linked list in memory, which it seems should be doable in a much more straightforward way. In fact since the list of CAFs will not change in run-time, it should be possible to initialize it in compile time as:

    ENTRY entry_0[1] = { ..., link = NULL };
ENTRY entry_1[1] = { ..., link = entry_0 };
...
head = entry_n;

    And this is before wondering why not use an array of entries instead of a linked list in the 1st place. That said, I am just guessing here, I have no understanding of what is really going on, other than the fact I was forced to add {-# OPTIONS_GHC -optc -O0 #-} to the offending file.

    Attached is a tgz file containing the generated C code (plus a version which is post-CPP, so you can just try to compile it in various ways on systems without GHC installed).

    Edited
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