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GCC Explorer - an interactive take on compilationGCC Explorer - an interactive take on compilationPosted May 25, 2012 8:48 UTC (Fri) by ekj (guest, #1524)In reply to: GCC Explorer - an interactive take on compilation by Richard_J_Neill Parent article: GCC Explorer - an interactive take on compilation
It's not enough to invoke it and notice that it returns "blablah 42\n". To be able to optimise it away, gcc would have to be certain that it -always- returns precisely that. (not just that it did, this time)
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GCC Explorer - an interactive take on compilation Posted May 25, 2012 15:20 UTC (Fri) by jimparis (subscriber, #38647) [Link]
Even more to the point, printf doesn't actually return "blablah 42\n" at all -- it writes it to stdout as a side-effect. So you can't even say "simulate execution and see the result" without knowing that a particular small piece of inline assembly deep inside the libc stdio that was called near the end of printf() execution happens to trigger kernel magic. It's really just not feasible to do this type of optimization in the general case. And it's just impossible in this specific case, as mentioned by khim.
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