Fix SafeHeap crash when start function calls an imported function

src/passes/SafeHeap.cpp

@@ -139,6 +139,9 @@ static std::set<Name> findCalledFunctions(Module* module, Name startFunc) {
       auto next = toVisit.back();
       toVisit.pop_back();
       auto* func = module->getFunction(next);
+      if (func->imported()) {
+        continue;
+      }
       for (auto* call : FindAll<Call>(func->body).list) {
         addFunction(call->target);
       }

test/lit/passes/safe-heap-start-import.wast

@@ -0,0 +1,25 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --safe-heap -S -o - | filecheck %s
+
+;; Test that safe-heap does not crash when the start function calls an imported
+;; function. The findCalledFunctions helper transitively walks all called
+;; functions from the start, and must skip imported functions which have no body.
+
+(module
+  ;; CHECK:      (import "env" "some_import" (func $import))
+  (import "env" "some_import" (func $import))
+  (memory 1 1)
+
+  ;; CHECK:      (start $start)
+  (start $start)
+
+  ;; CHECK:      (func $start
+  ;; CHECK-NEXT:  (call $import)
+  ;; CHECK-NEXT: )
+  (func $start
+    ;; The start function calls an imported function. Previously this would
+    ;; crash because findCalledFunctions would try to walk the null body of
+    ;; the imported function.
+    (call $import)
+  )
+)