Add EH support for CodeFolding (#2665)

This does two things:
- Treats the target branch of `br_on_exn` as unoptimizables, because it
  is a conditional branch.
- Makes sure we don't move expressions that contain `exnref.pop`, which
  should follow right after `catch`.
- Adds `containsChild` utility function, which can search all children,
  optionally with limited depth. This was actually added to be used in
  CodeFolding but ended up not being used, but wasn't removed in case
  there will be uses later.

2 files changed, 125 insertions, 0 deletions

diff --git a/test/passes/remove-unused-names_code-folding.txt b/test/passes/remove-unused-names_code-folding_all-features.txt
index 93f503579..2aa40da24 100644
--- a/test/passes/remove-unused-names_code-folding.txt
+++ b/test/passes/remove-unused-names_code-folding_all-features.txt
@@ -3,6 +3,7 @@
  (type $none_=>_i32 (func (result i32)))
  (type $i32_=>_i32 (func (param i32) (result i32)))
  (type $i32_i32_=>_i32 (func (param i32 i32) (result i32)))
+ (event $e (attr 0) (param))
  (func $ifs (; 0 ;)
   (if
    (i32.const 0)
@@ -1708,4 +1709,78 @@
    (i32.const 2)
   )
  )
+ (func $exnref_pop_test (; 36 ;)
+  (local $exn exnref)
+  (block $folding-inner0
+   (try
+    (try
+     (nop)
+     (catch
+      (local.set $exn
+       (exnref.pop)
+      )
+      (br $folding-inner0)
+     )
+    )
+    (catch
+     (local.set $exn
+      (exnref.pop)
+     )
+     (br $folding-inner0)
+    )
+   )
+   (return)
+  )
+  (drop
+   (i32.const 111)
+  )
+  (drop
+   (i32.const 222)
+  )
+  (drop
+   (i32.const 333)
+  )
+  (unreachable)
+ )
+ (func $br_on_exn_target_block (; 37 ;)
+  (local $exn exnref)
+  (block $x
+   (if
+    (i32.const 0)
+    (block
+     (drop
+      (i32.const 1)
+     )
+     (drop
+      (i32.const 2)
+     )
+     (br $x)
+    )
+   )
+   (if
+    (i32.const 0)
+    (block
+     (drop
+      (i32.const 1)
+     )
+     (drop
+      (i32.const 2)
+     )
+     (br $x)
+    )
+   )
+   (drop
+    (br_on_exn $x $e
+     (local.get $exn)
+    )
+   )
+   (drop
+    (i32.const 1)
+   )
+   (drop
+    (i32.const 2)
+   )
+   (br $x)
+  )
+ )
 )
diff --git a/test/passes/remove-unused-names_code-folding.wast b/test/passes/remove-unused-names_code-folding_all-features.wast
index 9979a0a3c..ad803864e 100644
--- a/test/passes/remove-unused-names_code-folding.wast
+++ b/test/passes/remove-unused-names_code-folding_all-features.wast
@@ -1191,4 +1191,54 @@
       )
     )
   )
+
+  (func $exnref_pop_test (local $exn exnref)
+    (try
+      (try
+        (catch
+          ;; Expressions containing exnref.pop should NOT be taken out and
+          ;; folded.
+          (local.set $exn (exnref.pop))
+          (drop (i32.const 111))
+          (drop (i32.const 222))
+          (drop (i32.const 333))
+          (unreachable)
+        )
+      )
+      (catch
+        (local.set $exn (exnref.pop))
+        (drop (i32.const 111))
+        (drop (i32.const 222))
+        (drop (i32.const 333))
+        (unreachable)
+      )
+    )
+  )
+
+  (event $e (attr 0)) ;; exception with no param
+  (func $br_on_exn_target_block (local $exn exnref)
+    ;; Here this block $x is targeted by br_on_exn, so code folding out of this
+    ;; block should NOT happen.
+    (block $x
+      (if (i32.const 0)
+        (block
+          (drop (i32.const 1))
+          (drop (i32.const 2))
+          (br $x)
+        )
+      )
+      (if (i32.const 0)
+        (block
+          (drop (i32.const 1))
+          (drop (i32.const 2))
+          (br $x)
+        )
+      )
+      (drop (br_on_exn $x $e (local.get $exn)))
+      ;; no fallthrough, another thing to merge
+      (drop (i32.const 1))
+      (drop (i32.const 2))
+      (br $x)
+    )
+  )
 )