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by haberman 5216 days ago
Out of curiosity, if someone paid you to find compiler bugs for a day, how would you go about it?

(I've found several missed-optimization bugs in gcc, but I found them while working on a project where I examine assembly frequently; I have no idea how I'd go about looking for a compiler bug).
1 comments
mansr 5216 days ago
One way of actively looking for compiler bugs is using a tool like Csmith[1]. Another is to compile some known-difficult code (e.g. Libav[2]) with various combinations of (optimisation) flags until the test suite fails. Most of the bugs I've found were during routine testing of Libav.

While I don't consider missed optimisations bugs as such, they are easy to find. Simply compile some non-trivial function and look at the output. There's usually something that could be done better, especially if some exotic instruction can be used.

[1] http://embed.cs.utah.edu/csmith/ [2] http://libav.org/

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haberman 5215 days ago
> While I don't consider missed optimisations bugs as such, they are easy to find. Simply compile some non-trivial function and look at the output.

Perhaps you'll give me a little credit :) if I mention that I found missed optimization bugs in extremely trivial functions. One of them involved gcc generating several completely useless stores even at -O3: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44194

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mansr 5214 days ago
That's not "missed optimisation," that's "generating ridiculous code."
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