bytecodealliance
Fuzzer Not Detecting Incorrect Allocation
It's possible for vregs to be used or defined in branch instructions, but the fuzzer doesn't seem to check for these operands.
The following doesn't pass the fuzzer:
block0:
0. branch(1). operands: [def v0 (fixed: p0)] // Allocation: [v0: p0]
block1:
1. operands: [use v0 (fixed: p0)] // Allocation: [v0: p0]
And this does:
block0:
0. operand: [def v0 (fixed: p0)] // Allocation: [v0: p0]
1. branch(1). operands: [use v0 (fixed: p1)] // Allocation: [v0: p9]
block1:
2. operands: [use v0 (fixed: p0)] // Allocation: [v0: p0]
Which is incorrect.
To reproduce this, run the tests in src/fastalloc/tests.rs at https://github.com/d-sonuga/regalloc2/tree/975dee0ceb56bbc6cbd21554a237babe1e388573.
To resolve this issue, one of the following could be done:
- Disallow operands in branch instructions.
- Update the fuzzer to check for these operands.
Indeed, it seems we skip checking operands on branch instructions: link
The stated reason there is that we don't want to check block arguments as normal uses, because we handle them separately (translating to ParallelMove checker instructions); but there's no reason we can't iterate over non-block-arg operands and handle them normally. I'm happy to review a PR for that if you want to try! Or alternately I'm happy to make the change.
@Amanieu ah, yes, thanks for that reminder; would you be willing to separate out the checker changes in #170 from the blockparam restrictions and post them in a separate PR?