The flag-based early-return rewriter was tied to one specific lowered shape:
the try body's flag-setter had to be exactly `stloc flag(K); leave try`, the
post-try check had to be a `br checkBlock` (not an inline `IfInstruction`), and
the early path had to be a direct Leave or a forward to a one-instruction
leave-block whose target was the function body. None of those hold for
`try { try { return X; } finally { await ... } } finally { await ... }`:
- The inner flag-setter has a leading capture-forwarding store
(`stloc capture(X); stloc innerFlag(K); leave inner-try`).
- The inner check-block's early path branches to a multi-instruction helper
that sets the *outer* flag and leaves the outer try, instead of being a
direct return.
- SplitVariables hands out a separate ILVariable for the pre-init flag store
when the in-handler store is in a disjoint dataflow region.
Rebuild the matcher around the idea of a "template" — the chain of stores
the early path performs before its terminating Leave. Each flag-setter then
becomes its own prefix stores + a clone of the template, which collapses the
inner-then-outer flag chain in two passes (inner first, outer second, because
descendant order visits the inner TryFinally first). Also extend the
flag-setter scan to walk the whole try-block's descendants — after the inner
rewrite, the inner's spliced flag-setter lives inside the inner-try container
but still leaves outwards to the outer try, so it's an outer flag-setter from
the outer's perspective.
Add a `RUNTIMEASYNC` preprocessor symbol (defined when `EnableRuntimeAsync`
is set) and gate the new return-from-try-finally fixtures on it — the
state-machine async pipeline doesn't recover this shape, so it would expand
the same source into the `int result; try { ...; result = X; } finally { ... }
return result;` verbose form and the Async (state-machine) pretty test would
regress.
Closes Cluster 1 (1.1, 1.3) from #3745. Cluster 1.2 (void `return;` at the
end of a try-finally body) and 1.4 (break/continue across a try-finally) are
left for a follow-up: both round-trip semantically equivalently but the AST
emitter drops a trailing void `return;` and the break/continue lowering uses
a switch dispatch that the current single-K matcher can't recognize.
Siegfried Pammer
8e2e48f5cc