diff options
Diffstat (limited to 'src/passes/OptimizeInstructions.cpp')
| -rw-r--r-- | src/passes/OptimizeInstructions.cpp | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp index 6251348af..acb2c8d66 100644 --- a/src/passes/OptimizeInstructions.cpp +++ b/src/passes/OptimizeInstructions.cpp @@ -1615,9 +1615,27 @@ struct OptimizeInstructions // TODO Worth thinking about an 'assume' instrinsic of some form that // annotates knowledge about a value, or another mechanism to allow // that information to be passed around. + + // Note that we must check that the null is actually flowed out, that is, + // that control flow is not transferred before: + // + // (if + // (1) + // (block (result null) + // (return) + // ) + // (other)) + // + // The true arm has a bottom type, but in fact it just returns out of the + // function and the null does not actually flow out. We can only optimize + // here if a null definitely flows out (as only that would cause a trap). + auto flowsOutNull = [&](Expression* child) { + return child->type.isNull() && !effects(child).transfersControlFlow(); + }; + if (auto* iff = ref->dynCast<If>()) { if (iff->ifFalse) { - if (iff->ifTrue->type.isNull()) { + if (flowsOutNull(iff->ifTrue)) { if (ref->type != iff->ifFalse->type) { refinalize = true; } @@ -1625,7 +1643,7 @@ struct OptimizeInstructions iff->ifFalse); return false; } - if (iff->ifFalse->type.isNull()) { + if (flowsOutNull(iff->ifFalse)) { if (ref->type != iff->ifTrue->type) { refinalize = true; } @@ -1641,7 +1659,7 @@ struct OptimizeInstructions // refinalize only happens at the end. That is, the select may stil be // reachable after we turned one child into an unreachable, and we are // calling getResultOfFirst which will error on unreachability. - if (select->ifTrue->type.isNull() && + if (flowsOutNull(select->ifTrue) && select->ifFalse->type != Type::unreachable) { ref = builder.makeSequence( builder.makeDrop(select->ifTrue), @@ -1649,7 +1667,7 @@ struct OptimizeInstructions builder.makeDrop(select->condition))); return false; } - if (select->ifFalse->type.isNull() && + if (flowsOutNull(select->ifFalse) && select->ifTrue->type != Type::unreachable) { ref = getResultOfFirst( select->ifTrue, |