fix handling of an if in a tee without an else, in coalesce-locals

Author: kripken

src/passes/CoalesceLocals.cpp

@@ -196,7 +196,9 @@ struct CoalesceLocals : public WalkerPass<CFGWalker<CoalesceLocals, Visitor<Coal
     if (auto* get = set->value->dynCast<GetLocal>()) return get;
     if (auto* iff = set->value->dynCast<If>()) {
       if (auto* get = iff->ifTrue->dynCast<GetLocal>()) return get;
-      if (auto* get = iff->ifFalse->dynCast<GetLocal>()) return get;
+      if (iff->ifFalse) {
+        if (auto* get = iff->ifFalse->dynCast<GetLocal>()) return get;
+      }
     }
     return nullptr;
   }

test/passes/coalesce-locals.txt

@@ -1112,4 +1112,14 @@
   )
   (i32.const 1)
  )
+ (func $unused-tee-with-child-if-no-else (type $4) (param $0 i32)
+  (loop $label$0
+   (drop
+    (if
+     (br $label$0)
+     (nop)
+    )
+   )
+  )
+ )
 )

test/passes/coalesce-locals.wast

@@ -1085,4 +1085,16 @@
     )
     (i32.const 1)
   )
+  (func $unused-tee-with-child-if-no-else (param $0 i32)
+   (loop $label$0
+    (drop
+     (tee_local $0
+      (if
+       (br $label$0)
+       (nop)
+      )
+     )
+    )
+   )
+  )
 )