[bigmac]

Their idea to checksum the global variables is really clever. Many benchmarks and testsuites simply rely on verifying program output. They're able to verify a greater surface area of the compiler by ensuring that all the intermediate global values used in their random programs have the same values at the end of the computation.

Its not in the slides, but during the Q&A they revealed that far fewer bugs were found in gcc than in LLVM. With compilers, as with most software, battle-tested dinosaurs win the day when it comes to code quality.

Its also interesting to note that the greatest number of bugs were found in the InstCombine pass, which has been completely refactored. In LLVM2.6 it was one monolithic source code file (13000 lines) with a zillion different peephole optimizations. Now its broken up into 15 files.

[regehr]

Another reason we reported more bugs to LLVM is that on average, they fixed bugs faster.