handle an unreachable condition properly in vacuum if simplification

Author: kripken

src/passes/Vacuum.cpp

@@ -232,6 +232,12 @@ struct Vacuum : public WalkerPass<PostWalker<Vacuum>> {
       replaceCurrent(child);
       return;
     }
+    // if the condition is unreachable, just return it
+    if (curr->condition->type == unreachable) {
+      replaceCurrent(curr->condition);
+      return;
+    }
+    // from here on, we can assume the condition executed
     if (curr->ifFalse) {
       if (curr->ifFalse->is<Nop>()) {
         curr->ifFalse = nullptr;

test/passes/vacuum.txt

@@ -273,4 +273,18 @@
    )
   )
  )
+ (func $unreachable-if-with-nop-arm-that-leaves-a-concrete-value-if-nop-is-removed (type $0)
+  (block $label$0
+   (loop $label$1
+    (br_if $label$0
+     (i32.load8_s
+      (i32.const 1634541608)
+     )
+     (loop $label$9
+      (br $label$9)
+     )
+    )
+   )
+  )
+ )
 )

test/passes/vacuum.wast

@@ -593,4 +593,22 @@
     )
    )
   )
+  (func $unreachable-if-with-nop-arm-that-leaves-a-concrete-value-if-nop-is-removed
+   (block $label$0
+    (loop $label$1
+     (if
+      (br_if $label$0
+       (i32.load8_s
+        (i32.const 1634541608)
+       )
+       (loop $label$9
+        (br $label$9)
+       )
+      )
+      (nop)
+      (i32.const 1920103026)
+     )
+    )
+   )
+  )
 )