Fix fallback-split behavior: trim start of minimal bundle wrt start of original LR.#85
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cfallin merged 1 commit intobytecodealliance:mainfrom Sep 22, 2022
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…f original LR. When a liverange starts at a *late* point of an instruction, and it undergoes the fallback "split into all minimal pieces" transform, we end up creating one minimal bundle that starts at the *early* point of the instruction at the start of the original LR. This can create impossible-to-allocate situations where a fixed-constraint LR overlaps another constrained to the same register (e.g. at calls). We fix this by ensuring the minimal bundle is trimmed only to the half of the instruction that overlaps the original LR. This is analogous to the third fix in bytecodealliance#74, but on the other end (start of LR rather than end of it).
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This fixes a fuzzbug (https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=51699 for those with access) and thus a compile panic on |
jameysharp
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Hey, I actually understood this one!
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cfallin
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Sep 22, 2022
Incorporates bytecodealliance/regalloc2#85, which fixes a fuzzbug related to constraints and liverange splits.
cfallin
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Sep 23, 2022
* Upgrade to regalloc2 0.4.1. Incorporates bytecodealliance/regalloc2#85, which fixes a fuzzbug related to constraints and liverange splits. * Add audit of regalloc2 upgrade.
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When a liverange starts at a late point of an instruction, and it undergoes the fallback "split into all minimal pieces" transform, we end up creating one minimal bundle that starts at the early point of the instruction at the start of the original LR. This can create impossible-to-allocate situations where a fixed-constraint LR overlaps another constrained to the same register (e.g. at calls). We fix this by ensuring the minimal bundle is trimmed only to the half of the instruction that overlaps the original LR.
This is analogous to the third fix in #74, but on the other end (start of LR rather than end of it).