Prevent pops from sinking in SimplifyLocals (#2885)

This prevents `exnref.pop`s from being sinked and separated from
`catch`. For example,
```wast
(try
  (do)
  (catch
    (local.set $0 (exnref.pop))
    (call $foo
      (i32.const 3)
      (local.get $0)
    )
  )
)
```
Here, if we sink `exnref.pop` to remove `local.set $0` and
`local.get $0`, it becomes this:
```wast
(try
  (do)
  (catch
    (nop)
    (call $foo
      (i32.const 3)
      (exnref.pop)
    )
  )
)
```
This move was possible because `i32.const 3` does not have any side
effects. But this is incorrect because now `exnref.pop` does not follow
right after `catch`.

To prevent this, this patch checks this case in `canSink` in
SimplifyLocals. When we encountered a similar case in CodeFolding, we
prevented every expression that contains `Pop` anywhere in it from being
moved, which was too conservative. This adds `danglingPop` property in
`EffectAnalyzer`, so that only pops that are not enclosed within a
`catch` count as 'dangling pops` and we only prevent those pops from
being moved or sinked.

2 files changed, 12 insertions, 1 deletions

diff --git a/test/binaryen.js/sideffects.js b/test/binaryen.js/sideffects.js
index 76bc1db68..bfb5404c2 100644
--- a/test/binaryen.js/sideffects.js
+++ b/test/binaryen.js/sideffects.js
@@ -10,6 +10,7 @@ console.log("SideEffects.WritesMemory=" + binaryen.SideEffects.WritesMemory);
 console.log("SideEffects.ImplicitTrap=" + binaryen.SideEffects.ImplicitTrap);
 console.log("SideEffects.IsAtomic=" + binaryen.SideEffects.IsAtomic);
 console.log("SideEffects.Throws=" + binaryen.SideEffects.Throws);
+console.log("SideEffects.DanglingPop=" + binaryen.SideEffects.DanglingPop);
 console.log("SideEffects.Any=" + binaryen.SideEffects.Any);
 
 var module = new binaryen.Module();
@@ -104,3 +105,12 @@ assert(
   ==
   binaryen.SideEffects.Calls | binaryen.SideEffects.Throws
 );
+
+assert(
+  binaryen.getSideEffects(
+    module.drop(module.exnref.pop()),
+    module.getFeatures()
+  )
+  ==
+  binaryen.SideEffects.DanglingPop
+);
diff --git a/test/binaryen.js/sideffects.js.txt b/test/binaryen.js/sideffects.js.txt
index 4aca0ac46..53ee474e5 100644
--- a/test/binaryen.js/sideffects.js.txt
+++ b/test/binaryen.js/sideffects.js.txt
@@ -10,4 +10,5 @@ SideEffects.WritesMemory=128
 SideEffects.ImplicitTrap=256
 SideEffects.IsAtomic=512
 SideEffects.Throws=1024
-SideEffects.Any=2047
+SideEffects.DanglingPop=2048
+SideEffects.Any=4095