[EH] Fix binary parsing for catchless try + inner delegate (#4370)

We do some postprocessing after parsing `Try` to make sure `delegate`
only targets `try`s and not `block`s:
https://github.com/WebAssembly/binaryen/blob/9659f9b07c1196447edee68fe04c8d7dd2480652/src/wasm/wasm-binary.cpp#L6404-L6426

But in case the outer `try` has neither of `catch` nor `delegate`, the
previous code just return prematurely, skipping the postprocessing part,
resulting in a binary parsing error. This PR removes that early-exiting
code.

Some test outputs have changed because `try`s are assigned labels after
the early exit. But those labels can be removed by other optimization
passes when there is no inner `rethrow` or `delegate` that targets them.

(On a side note, the restriction that `delegate` cannot target a `block`
has been removed a few months ago in the spec, so if a `delegate`
targets a `block`, it means it is just rethrown from that block. But I
still think this is a convenient invariant to hold at least within the
binaryen IR. I'm planning to allow parsing of `delegate` targeting
`block`s later, but I will make them point to `try` when read in the
IR. At the moment the LLVM toolchain does not generate such code.)

1 files changed, 19 insertions, 3 deletions

diff --git a/test/exception-handling.wast.fromBinary b/test/exception-handling.wast.fromBinary
index 9a89a0beb..29231a943 100644
--- a/test/exception-handling.wast.fromBinary
+++ b/test/exception-handling.wast.fromBinary
@@ -15,7 +15,7 @@
  (func $bar
   (nop)
  )
- (func $eh_test
+ (func $eh-test
   (local $x i32)
   (local $1 i64)
   (local $2 (i32 i64))
@@ -197,7 +197,7 @@
     )
    )
   )
-  (try
+  (try $label$37
    (do
     (throw $tag$0
      (i32.const 0)
@@ -382,7 +382,7 @@
    )
   )
  )
- (func $pop_test
+ (func $pop-test
   (try $label$5
    (do
     (nop)
@@ -408,5 +408,21 @@
    )
   )
  )
+ (func $catchless-try-with-inner-delegate
+  (try $label$6
+   (do
+    (block $label$1
+     (try $label$4
+      (do
+       (throw $tag$0
+        (i32.const 0)
+       )
+      )
+      (delegate $label$6)
+     )
+    )
+   )
+  )
+ )
 )