Illuminating the processor core with LLVM-mca

(abseil.io)

64 points | by ckennelly 1 day ago

4 comments

  • KeplerBoy 1 day ago
    Also nicely demonstrated in godbolt's currently ongoing Advent of compiler optimizations series.
  • fweimer 22 hours ago
    Wouldn't LLVM adjust the models if it is beneficial to its code generation, even if the result less accurately reflects the processor? (I think GCC does that.)
  • alain94040 1 day ago
    This is interesting if quite incomplete (as noted in the end conclusion). CPU re-order buffers turn what you think as mostly sequential execution into a massively parallel engine. Data memory access, perfecting, speculative execution, etc. But if you are running a micro-bencmark with a tight loop of millions of iterations, then understanding the pipeline dependencies and dispatching can provide good insights.
    • drob518 21 hours ago
      Yep. Cache is always the wildcard.
  • esbranson 1 day ago
    Too bad they don't support LC-3 or DLX. More my level lol. So begins another deep dive side quest with the chatbot into a tool I didn't even know existed.