4 ms·

Separate the backend into functional subcomponents and fuzz them as much as possible? It's what cranelift does.

• wyldfire 6y ago
  Fuzzing is great for finding crashes and other catastrophic misbehavior. But suboptimal codegen like this would be difficult to reveal with fuzzing. You could do it with a reference compiler (this has in fact been done before) but finding suboptimal codegen like this case would still be kinda tricky.
  • tom_mellior 6y ago
    Based on other comments this seems to be a regression in LLVM. LLVM does have a reference compiler for regressions: It's the previous version of LLVM. (Not saying that that makes this trivial.)
    • wyldfire 6y ago
      But if this next release makes codegen improvements, those would all show up as differences. Separating the improvements from the regressions is difficult enough -- fuzzing doesn't really help here, it makes it much harder to determine what code should have been generated. Generally, codegen issues are exposed by benchmarks or someone who is curious enough to examine and analyze the code generated from multiple compilers or multiple releases. The latter is much rarer. But as these happen, the bar keeps getting raised and we do grow the test suite.