diff --git a/js/src/ds/InlineTable.h b/js/src/ds/InlineTable.h
index 874efd537052..b1b7f136f419 100644
--- a/js/src/ds/InlineTable.h
+++ b/js/src/ds/InlineTable.h
@@ -218,11 +218,6 @@ class InlineTable : private AllocPolicy {
     inlCount_ = 0;
   }
 
-  void clearAndCompact() {
-    clear();
-    table_.clearAndCompact();
-  }
-
   MOZ_ALWAYS_INLINE
   Ptr lookup(const Lookup& l) {
     MOZ_ASSERT(keyNonZero(l));
@@ -480,8 +475,6 @@ class InlineMap {
 
   void clear() { impl_.clear(); }
 
-  void clearAndCompact() { impl_.clearAndCompact(); }
-
   Range all() const { return impl_.all(); }
 
   MOZ_ALWAYS_INLINE
@@ -586,8 +579,6 @@ class InlineSet {
 
   void clear() { impl_.clear(); }
 
-  void clearAndCompact() { impl_.clearAndCompact(); }
-
   Range all() const { return impl_.all(); }
 
   MOZ_ALWAYS_INLINE
diff --git a/js/src/jit-test/tests/ion/bug1598784.js b/js/src/jit-test/tests/ion/bug1598784.js
new file mode 100644
index 000000000000..20803e2f09fb
--- /dev/null
+++ b/js/src/jit-test/tests/ion/bug1598784.js
@@ -0,0 +1,8 @@
+// |jit-test| error:ReferenceError
+(function() {
+    switch (0) {
+        case 0:
+            f() = 0;
+        case -3:
+    }
+})();
diff --git a/js/src/jit/Ion.cpp b/js/src/jit/Ion.cpp
index 8d21c6e30d1f..2fdb134afd5d 100644
--- a/js/src/jit/Ion.cpp
+++ b/js/src/jit/Ion.cpp
@@ -424,7 +424,7 @@ void jit::FreeIonBuilder(IonBuilder* builder) {
   // destroy the builder and all other data accumulated during compilation,
   // except any final codegen (which includes an assembler and needs to be
   // explicitly destroyed).
-  MOZ_ASSERT(builder->pendingEdges().empty(), "Should not leak malloc memory");
+  MOZ_ASSERT(!builder->hasPendingEdgesMap(), "Should not leak malloc memory");
   js_delete(builder->backgroundCodegen());
   js_delete(builder->alloc().lifoAlloc());
 }
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index d246d53b43ff..88e81d457b5b 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -1623,8 +1623,9 @@ AbortReasonOr<Ok> IonBuilder::traverseBytecode() {
 
   // IonBuilder's destructor is not called, so make sure pendingEdges_ and
   // GSNCache are not holding onto malloc memory when we return.
+  pendingEdges_.emplace();
   auto freeMemory = mozilla::MakeScopeExit([&] {
-    pendingEdges_.clearAndCompact();
+    pendingEdges_.reset();
     gsn.purge();
   });
 
@@ -1748,7 +1749,7 @@ AbortReasonOr<Ok> IonBuilder::jsop_goto(bool* restarted) {
 
 AbortReasonOr<Ok> IonBuilder::addPendingEdge(const PendingEdge& edge,
                                              jsbytecode* target) {
-  PendingEdgesMap::AddPtr p = pendingEdges_.lookupForAdd(target);
+  PendingEdgesMap::AddPtr p = pendingEdges_->lookupForAdd(target);
   if (p) {
     if (!p->value().append(edge)) {
       return abort(AbortReason::Alloc);
@@ -1761,7 +1762,7 @@ AbortReasonOr<Ok> IonBuilder::addPendingEdge(const PendingEdge& edge,
                 "Appending one element should be infallible");
   MOZ_ALWAYS_TRUE(edges.append(edge));
 
-  if (!pendingEdges_.add(p, target, std::move(edges))) {
+  if (!pendingEdges_->add(p, target, std::move(edges))) {
     return abort(AbortReason::Alloc);
   }
   return Ok();
@@ -2798,7 +2799,7 @@ AbortReasonOr<Ok> IonBuilder::restartLoop(MBasicBlock* header) {
   }
 
   // Remove loop header and dead blocks from pendingBlocks.
-  for (PendingEdgesMap::Range r = pendingEdges_.all(); !r.empty();
+  for (PendingEdgesMap::Range r = pendingEdges_->all(); !r.empty();
        r.popFront()) {
     PendingEdges& blocks = r.front().value();
     for (size_t i = blocks.length(); i > 0; i--) {
@@ -3475,14 +3476,14 @@ AbortReasonOr<Ok> IonBuilder::visitTry() {
 }
 
 AbortReasonOr<Ok> IonBuilder::visitJumpTarget(JSOp op) {
-  PendingEdgesMap::Ptr p = pendingEdges_.lookup(pc);
+  PendingEdgesMap::Ptr p = pendingEdges_->lookup(pc);
   if (!p) {
     // No (reachable) jumps so this is just a no-op.
     return Ok();
   }
 
   PendingEdges edges(std::move(p->value()));
-  pendingEdges_.remove(p);
+  pendingEdges_->remove(p);
 
   MBasicBlock* joinBlock = nullptr;
 
diff --git a/js/src/jit/IonBuilder.h b/js/src/jit/IonBuilder.h
index add61831d18b..823ea9d4fa17 100644
--- a/js/src/jit/IonBuilder.h
+++ b/js/src/jit/IonBuilder.h
@@ -1255,7 +1255,7 @@ class IonBuilder : public MIRGenerator,
 
   uint32_t loopDepth_;
 
-  PendingEdgesMap pendingEdges_;
+  mozilla::Maybe<PendingEdgesMap> pendingEdges_;
   LoopStateStack loopStack_;
 
   Vector<BytecodeSite*, 0, JitAllocPolicy> trackedOptimizationSites_;
@@ -1438,7 +1438,7 @@ class IonBuilder : public MIRGenerator,
   void trackInlineSuccessUnchecked(InliningStatus status);
 
  public:
-  const PendingEdgesMap& pendingEdges() const { return pendingEdges_; }
+  bool hasPendingEdgesMap() const { return pendingEdges_.isSome(); }
 
   // This is only valid for IonBuilders that have moved to background
   size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;