Code Pushing: Ignore unreachable sets (#5284)

Normally we ignore them anyhow (unreachability is an effect, either a trap or
a control flow switch), but in traps-never-happen mode we can ignore a trap, so
we need to check this manually.

2 files changed, 49 insertions, 1 deletions

diff --git a/src/passes/CodePushing.cpp b/src/passes/CodePushing.cpp
index 20f16b145..2b45dda16 100644
--- a/src/passes/CodePushing.cpp
+++ b/src/passes/CodePushing.cpp
@@ -323,6 +323,26 @@ private:
       assert(i > 0);
       i--;
       auto* pushable = isPushable(list[i]);
+      if (pushable && pushable->type == Type::unreachable) {
+        // Don't try to push something unreachable. If we did, then we'd need to
+        // refinalize the block we are moving it from:
+        //
+        //  (block $unreachable
+        //    (local.set $x (unreachable))
+        //    (if (..)
+        //      (.. (local.get $x))
+        //  )
+        //
+        // The block should not be unreachable if the local.set is moved into
+        // the if arm (the if arm may not execute, so the if itself will not
+        // change type). It is simpler to avoid this complexity and leave this
+        // to DCE to simplify first.
+        //
+        // (Note that the side effect of trapping will normally prevent us from
+        // trying to push something unreachable, but in traps-never-happen mode
+        // we are allowed to ignore that, and so we need this check.)
+        pushable = nullptr;
+      }
       if (!pushable) {
         // Something that is staying where it is, so anything we push later must
         // move past it. Note the effects and continue.
diff --git a/test/lit/passes/code-pushing_tnh.wast b/test/lit/passes/code-pushing_tnh.wast
index 9993c686b..17f69a466 100644
--- a/test/lit/passes/code-pushing_tnh.wast
+++ b/test/lit/passes/code-pushing_tnh.wast
@@ -6,6 +6,8 @@
 (module
   ;; CHECK:      (type $i32_i32_=>_none (func (param i32 i32)))
 
+  ;; CHECK:      (type $none_=>_none (func))
+
   ;; CHECK:      (func $div (param $x i32) (param $y i32)
   ;; CHECK-NEXT:  (local $temp i32)
   ;; CHECK-NEXT:  (block $block
@@ -44,5 +46,31 @@
       )
     )
   )
-)
 
+  ;; CHECK:      (func $unreachable-value
+  ;; CHECK-NEXT:  (local $x i32)
+  ;; CHECK-NEXT:  (local.tee $x
+  ;; CHECK-NEXT:   (unreachable)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (if
+  ;; CHECK-NEXT:   (i32.const 0)
+  ;; CHECK-NEXT:   (drop
+  ;; CHECK-NEXT:    (local.get $x)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $unreachable-value
+    (local $x i32)
+    ;; We should not push this into the if. (If we did, we'd need to refinalize
+    ;; the block, or we'd error; instead, leave this to DCE.)
+    (local.set $x
+      (unreachable)
+    )
+    (if
+      (i32.const 0)
+      (drop
+        (local.get $x)
+      )
+    )
+  )
+)