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Is it possible for this sort of thing to make it into the compilers? Seems like it might see much more usage that way.

• sanxiyn 8y ago
  AutoFDO is exactly that. Facebook's execuse to develop this is that AutoFDO didn't work well with HHVM, but that sounds like an AutoFDO bugfix, not a whole new project. I agree with you that it is better to work on AutoFDO, because it will see more wide usage.
  • ebikelaw 8y ago
    Their reasoning is interesting: they use exceptions. Google notoriously does not. I wonder if Google (and the other AutoFDO contributors, of course) have overlooked something crucial that the exception-using people need.
  • maxpan 8y ago
    In many cases BOLT complements AutoFDO. AutoFDO affects several optimizations, and code layout is just one of them. Another critical optimization influenced by AutoFDO/PGO is function inlining. After inlining a callee code profile is often different from a "pre-inlined" profile seen by the compiler, which prevents the compiler from making an optimal layout decisions. Since BOLT observes the code after all compiler optimizations, its decisions are not affected by context-sensitive inlined function behavior.