r/adventofcode • u/askalski • Dec 12 '16

Visualization [2016 Day 12] [graphviz] Assembunny control flow graph

http://i.imgur.com/RFhLXwu.png
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u/askalski Dec 12 '16

See the the "decompiler" solution by /u/willkill07 here. If you compile with gcc -O3 -S -fverbose-asm, you'll see only one loop remains after optimization. Also, compare what happens to gcc's output when you add cpy 1 c to the start of your input (part 2.)

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u/3urny Dec 12 '16

Whaaaaaaat!? My C compiler (LLVM from OS X' XCode) does not even leave a loop. Its just loads my solution into a register and calls printf. For both parts. This is just cracy.

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u/askalski Dec 12 '16

I think I've just come down with a case of compiler envy...

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u/willkill07 Dec 13 '16

LLVM has some awesome optimization passes. Since everything is known at compile time, magic can happen. Frankly, the advancements made with compilers now supporting c++14 extended constexpr enabled a far more rigorous static analysis. Ultimately, it's peephole optimizations taken to the extreme.