From d623ba4b075aa1d70113fc41172a9ed248e0011d Mon Sep 17 00:00:00 2001 From: Alon Zakai Date: Thu, 5 Jan 2023 13:20:31 -0800 Subject: [Wasm GC] Fix non-nullable cast optimizations with multiple children (#5396) This fixes an oversight in #5395 --- src/passes/OptimizeInstructions.cpp | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) (limited to 'src') diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp index c2142fe6c..916991ecb 100644 --- a/src/passes/OptimizeInstructions.cpp +++ b/src/passes/OptimizeInstructions.cpp @@ -1606,7 +1606,38 @@ struct OptimizeInstructions // Either way we trap here, but refining the type may have benefits later. if (ref->type.isNullable()) { if (auto* cast = ref->dynCast()) { - cast->type = Type(cast->type.getHeapType(), NonNullable); + // Note that we must be the last child of the parent, otherwise effects + // in the middle may need to remain: + // + // (struct.set + // (ref.cast null + // (call .. + // + // The call here must execute before the trap in the struct.set. To + // avoid that problem, inspect all children after us. If there are no + // such children, then there is no problem; if there are, see below. + auto canOptimize = true; + auto seenRef = false; + for (auto* child : ChildIterator(curr)) { + if (child == ref) { + seenRef = true; + } else if (seenRef) { + // This is a child after the reference. Check it for effects. For + // simplicity, focus on the case of traps-never-happens: if we can + // assume no trap occurs in the parent, then there must not be a + // trap in the child either, unless control flow transfers and we + // might not reach the parent. + // TODO: handle more cases. + if (!getPassOptions().trapsNeverHappen || + effects(child).transfersControlFlow()) { + canOptimize = false; + break; + } + } + } + if (canOptimize) { + cast->type = Type(cast->type.getHeapType(), NonNullable); + } } } -- cgit v1.2.3