diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/passes/SimplifyLocals.cpp | 41 |
1 files changed, 38 insertions, 3 deletions
diff --git a/src/passes/SimplifyLocals.cpp b/src/passes/SimplifyLocals.cpp index 35980f503..5cf3b8241 100644 --- a/src/passes/SimplifyLocals.cpp +++ b/src/passes/SimplifyLocals.cpp @@ -299,12 +299,47 @@ struct SimplifyLocals Expression** currp) { Expression* curr = *currp; - // Expressions that may throw cannot be sinked into 'try'. At the start of - // 'try', we drop all sinkables that may throw. + // Certain expressions cannot be sinked into 'try', and so at the start of + // 'try' we forget about them. if (curr->is<Try>()) { std::vector<Index> invalidated; for (auto& [index, info] : self->sinkables) { - if (info.effects.throws()) { + // Expressions that may throw cannot be moved into a try (which might + // catch them, unlike before the move). + // + // Also, non-nullable local.sets cannot be moved into a try, as that may + // change dominance from the perspective of the spec + // + // (local.set $x X) + // (try + // .. + // (Y + // (local.get $x)) + // (catch + // (Z + // (local.get $x))) + // + // => + // + // (try + // .. + // (Y + // (local.tee $x X)) + // (catch + // (Z + // (local.get $x))) + // + // After sinking the set, the tee does not dominate the get in the + // catch, at least not in the simple way the spec defines it, see + // https://github.com/WebAssembly/function-references/issues/44#issuecomment-1083146887 + // We have more refined information about control flow and dominance + // than the spec, and so we would see if ".." can throw or not (only if + // it can throw is there a branch to the catch, which can change + // dominance). To stay compliant with the spec, however, we must not + // move code regardless of whether ".." can throw - we must simply keep + // the set outside of the try. + if (info.effects.throws() || + self->getFunction()->getLocalType(index).isNonNullable()) { invalidated.push_back(index); } } |