Improve the generation of fuzz functions#243
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cfallin merged 4 commits intobytecodealliance:mainfrom Sep 23, 2025
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Previously, the ranges of the knobs for generating components of a functions were hard-coded in `Func::arbitrary_with_options`. This change extracts some of them to `Options` to (a) allow for more control from outside and (b) to explain what these parameters are doing. The one functional change here is that `num_clobbers_per_inst = 0..=10` is used both times clobbers are created (callsite-ish arm and clobbers arm); previously the clobbers arm only clobbered `0..=5` registers. It seemed possible that this was just an oversight (?).
This change avoids iterating over the blocks twice--once will do fine. It is unclear, though, whether this loop should even exist: it seems like it is re-doing the "connect block successors and predecessors" work that `Func::add_edge` is already doing (TODO).
This is simply a readability refactor: the internal logic of `Func::arbitrary_with_options` is quite complex already, so moving some of the smaller pieces out into separate functions makes things clearer.
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Thanks for all of these cleanups!
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This is intended as a non-functional refactor (with one caveat below). The generation of functions is quite tricky:
regalloc2must always generate test case functions that are allocatable. But the complex logic ofFunc::arbitrary_with_optionsmakes this more difficult than it already is. This change attempts to simplify, document, and allow users of theFunc::arbitrary_with_optionsmore control over the generated test cases.The one caveat is the number of clobbers. Previously, we generated different amounts of clobbers if
opts.fixed_regs && opts.callsite_ish_constraintsand ifopts.clobbers:0..=10versus0..=5. I suspect this is an oversight (?) so I just used the sameopts.num_clobbers_per_instin both cases. This does change the fuzzing DNA, invalidating the corpus, but this will happen soon anyways if we start fuzzingOperandConstraint::Limit.