diff options
Diffstat (limited to 'src/passes/RemoveUnusedBrs.cpp')
| -rw-r--r-- | src/passes/RemoveUnusedBrs.cpp | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp index 2452130cc..2ccf3c761 100644 --- a/src/passes/RemoveUnusedBrs.cpp +++ b/src/passes/RemoveUnusedBrs.cpp @@ -898,8 +898,34 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> { auto glb = Type::getGreatestLowerBound(curr->castType, refType); if (glb != Type::unreachable && glb != curr->castType) { curr->castType = glb; + auto oldType = curr->type; curr->finalize(); worked = true; + + // We refined the castType, which may *un*-refine the BrOn itself. + // Imagine the castType was nullable before, then nulls would go on + // the branch, and so the BrOn could only flow out a non-nullable + // value, and that was its type. If we refine the castType to be + // non-nullable then nulls no longer go through, making the BrOn + // itself nullable. This should not normally happen, but can occur + // because we look at the fallthrough of the ref: + // + // (br_on_cast + // (local.tee $unrefined + // (refined + // + // That is, we may see a more refined type for our GLB computation + // than the wasm type system does, if a local.tee or such ends up + // unrefining the type. + // + // To check for this and fix it, see if we need a cast in order to be + // a subtype of the old type. + auto* rep = maybeCast(curr, oldType); + if (rep != curr) { + replaceCurrent(rep); + // Exit after doing so, leaving further work for other cycles. + return; + } } // Depending on what we know about the cast results, we may be able to |