diff a/src/hotspot/share/opto/loopUnswitch.cpp b/src/hotspot/share/opto/loopUnswitch.cpp
--- a/src/hotspot/share/opto/loopUnswitch.cpp
+++ b/src/hotspot/share/opto/loopUnswitch.cpp
@@ -22,10 +22,12 @@
  *
  */
 
 #include "precompiled.hpp"
 #include "memory/allocation.inline.hpp"
+#include "opto/mulnode.hpp"
+#include "opto/addnode.hpp"
 #include "opto/connode.hpp"
 #include "opto/convertnode.hpp"
 #include "opto/loopnode.hpp"
 #include "opto/opaquenode.hpp"
 #include "opto/predicates.hpp"
@@ -50,10 +52,11 @@
 //                                 endloop
 //                               endif
 //
 // Note: the "else" clause may be empty
 
+
 //------------------------------policy_unswitching-----------------------------
 // Return TRUE or FALSE if the loop should be unswitched
 // (ie. clone loop with an invariant test that does not exit the loop)
 bool IdealLoopTree::policy_unswitching( PhaseIdealLoop *phase ) const {
   if (!LoopUnswitching) {
@@ -73,21 +76,27 @@
 
   LoopNode* head = _head->as_Loop();
   if (head->unswitch_count() + 1 > head->unswitch_max()) {
     return false;
   }
-  if (phase->find_unswitching_candidate(this) == nullptr) {
+
+  if (head->is_flat_arrays()) {
+    return false;
+  }
+
+  Node_List unswitch_iffs;
+  if (phase->find_unswitching_candidate(this, unswitch_iffs) == nullptr) {
     return false;
   }
 
   // Too speculative if running low on nodes.
   return phase->may_require_nodes(est_loop_clone_sz(2));
 }
 
 //------------------------------find_unswitching_candidate-----------------------------
 // Find candidate "if" for unswitching
-IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop) const {
+IfNode* PhaseIdealLoop::find_unswitching_candidate(const IdealLoopTree *loop, Node_List& unswitch_iffs) const {
 
   // Find first invariant test that doesn't exit the loop
   LoopNode *head = loop->_head->as_Loop();
   IfNode* unswitch_iff = nullptr;
   Node* n = head->in(LoopNode::LoopBackControl);
@@ -108,10 +117,28 @@
         }
       }
     }
     n = n_dom;
   }
+  if (unswitch_iff != nullptr) {
+    unswitch_iffs.push(unswitch_iff);
+  }
+
+  // Collect all non-flat array checks for unswitching to create a fast loop
+  // without checks (only non-flat array accesses) and a slow loop with checks.
+  if (unswitch_iff == nullptr || unswitch_iff->is_flat_array_check(&_igvn)) {
+    for (uint i = 0; i < loop->_body.size(); i++) {
+      IfNode* n = loop->_body.at(i)->isa_If();
+      if (n != nullptr && n != unswitch_iff && n->is_flat_array_check(&_igvn) &&
+          loop->is_invariant(n->in(1)) && !loop->is_loop_exit(n)) {
+        unswitch_iffs.push(n);
+        if (unswitch_iff == nullptr) {
+          unswitch_iff = n;
+        }
+      }
+    }
+  }
   return unswitch_iff;
 }
 
 //------------------------------do_unswitching-----------------------------
 // Clone loop with an invariant test (that does not exit) and
@@ -122,69 +149,86 @@
   if (has_control_dependencies_from_predicates(head)) {
     return;
   }
 
   // Find first invariant test that doesn't exit the loop
-  IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop);
-  assert(unswitch_iff != nullptr, "should be at least one");
+  Node_List unswitch_iffs;
+  IfNode* unswitch_iff = find_unswitching_candidate((const IdealLoopTree *)loop, unswitch_iffs);
+  assert(unswitch_iff != nullptr && unswitch_iff == unswitch_iffs.at(0), "should be at least one");
+  bool flat_array_checks = unswitch_iffs.size() > 1;
 
 #ifndef PRODUCT
   if (TraceLoopOpts) {
     tty->print("Unswitch   %d ", head->unswitch_count()+1);
     loop->dump_head();
+    for (uint i = 0; i < unswitch_iffs.size(); i++) {
+      unswitch_iffs.at(i)->dump(3);
+      tty->cr();
+    }
   }
 #endif
 
   // Need to revert back to normal loop
   if (head->is_CountedLoop() && !head->as_CountedLoop()->is_normal_loop()) {
     head->as_CountedLoop()->set_normal_loop();
   }
 
-  IfNode* invar_iff = create_slow_version_of_loop(loop, old_new, unswitch_iff, CloneIncludesStripMined);
+  IfNode* invar_iff = create_slow_version_of_loop(loop, old_new, unswitch_iffs, CloneIncludesStripMined);
   ProjNode* proj_true = invar_iff->proj_out(1);
   verify_fast_loop(head, proj_true);
 
   // Increment unswitch count
   LoopNode* head_clone = old_new[head->_idx]->as_Loop();
   int nct = head->unswitch_count() + 1;
   head->set_unswitch_count(nct);
   head_clone->set_unswitch_count(nct);
 
-  // Hoist invariant casts out of each loop to the appropriate
-  // control projection.
-
+  // Hoist invariant casts out of each loop to the appropriate control projection.
   Node_List worklist;
-  for (DUIterator_Fast imax, i = unswitch_iff->fast_outs(imax); i < imax; i++) {
-    ProjNode* proj= unswitch_iff->fast_out(i)->as_Proj();
-    // Copy to a worklist for easier manipulation
-    for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
-      Node* use = proj->fast_out(j);
-      if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
-        worklist.push(use);
+  for (uint i = 0; i < unswitch_iffs.size(); i++) {
+    IfNode* iff = unswitch_iffs.at(i)->as_If();
+    for (DUIterator_Fast imax, i = iff->fast_outs(imax); i < imax; i++) {
+      ProjNode* proj = iff->fast_out(i)->as_Proj();
+      // Copy to a worklist for easier manipulation
+      for (DUIterator_Fast jmax, j = proj->fast_outs(jmax); j < jmax; j++) {
+        Node* use = proj->fast_out(j);
+        if (use->Opcode() == Op_CheckCastPP && loop->is_invariant(use->in(1))) {
+          worklist.push(use);
+        }
+      }
+      ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
+      while (worklist.size() > 0) {
+        Node* use = worklist.pop();
+        Node* nuse = use->clone();
+        nuse->set_req(0, invar_proj);
+        _igvn.replace_input_of(use, 1, nuse);
+        register_new_node(nuse, invar_proj);
+        // Same for the clone if we are removing checks from the slow loop
+        if (!flat_array_checks) {
+          Node* use_clone = old_new[use->_idx];
+          _igvn.replace_input_of(use_clone, 1, nuse);
+        }
       }
-    }
-    ProjNode* invar_proj = invar_iff->proj_out(proj->_con)->as_Proj();
-    while (worklist.size() > 0) {
-      Node* use = worklist.pop();
-      Node* nuse = use->clone();
-      nuse->set_req(0, invar_proj);
-      _igvn.replace_input_of(use, 1, nuse);
-      register_new_node(nuse, invar_proj);
-      // Same for the clone
-      Node* use_clone = old_new[use->_idx];
-      _igvn.replace_input_of(use_clone, 1, nuse);
     }
   }
 
   // Hardwire the control paths in the loops into if(true) and if(false)
-  _igvn.rehash_node_delayed(unswitch_iff);
-  dominated_by(proj_true->as_IfProj(), unswitch_iff, false, false);
-
+  for (uint i = 0; i < unswitch_iffs.size(); i++) {
+    IfNode* iff = unswitch_iffs.at(i)->as_If();
+    _igvn.rehash_node_delayed(iff);
+    dominated_by(proj_true->as_IfProj(), iff);
+  }
   IfNode* unswitch_iff_clone = old_new[unswitch_iff->_idx]->as_If();
-  _igvn.rehash_node_delayed(unswitch_iff_clone);
-  ProjNode* proj_false = invar_iff->proj_out(0);
-  dominated_by(proj_false->as_IfProj(), unswitch_iff_clone, false, false);
+  if (!flat_array_checks) {
+    ProjNode* proj_false = invar_iff->proj_out(0)->as_Proj();
+    _igvn.rehash_node_delayed(unswitch_iff_clone);
+    dominated_by(proj_false->as_IfProj(), unswitch_iff_clone);
+  } else {
+    // Leave the flat array checks in the slow loop and
+    // prevent it from being unswitched again based on these checks.
+    head_clone->mark_flat_arrays();
+  }
 
   // Reoptimize loops
   loop->record_for_igvn();
   for(int i = loop->_body.size() - 1; i >= 0 ; i--) {
     Node *n = loop->_body[i];
@@ -192,13 +236,15 @@
     _igvn._worklist.push(n_clone);
   }
 
 #ifndef PRODUCT
   if (TraceLoopUnswitching) {
-    tty->print_cr("Loop unswitching orig: %d @ %d  new: %d @ %d",
-                  head->_idx,                unswitch_iff->_idx,
-                  old_new[head->_idx]->_idx, unswitch_iff_clone->_idx);
+    for (uint i = 0; i < unswitch_iffs.size(); i++) {
+      tty->print_cr("Loop unswitching orig: %d @ %d  new: %d @ %d",
+                    head->_idx,                unswitch_iffs.at(i)->_idx,
+                    old_new[head->_idx]->_idx, old_new[unswitch_iffs.at(i)->_idx]->_idx);
+    }
   }
 #endif
 
   C->set_major_progress();
 }
@@ -221,24 +267,50 @@
 //-------------------------create_slow_version_of_loop------------------------
 // Create a slow version of the loop by cloning the loop
 // and inserting an if to select fast-slow versions.
 // Return the inserted if.
 IfNode* PhaseIdealLoop::create_slow_version_of_loop(IdealLoopTree *loop,
-                                                      Node_List &old_new,
-                                                      IfNode* unswitch_iff,
-                                                      CloneLoopMode mode) {
+                                                    Node_List &old_new,
+                                                    Node_List &unswitch_iffs,
+                                                    CloneLoopMode mode) {
   LoopNode* head  = loop->_head->as_Loop();
+  bool counted_loop = head->is_CountedLoop();
   Node*     entry = head->skip_strip_mined()->in(LoopNode::EntryControl);
   _igvn.rehash_node_delayed(entry);
   IdealLoopTree* outer_loop = loop->_parent;
 
   head->verify_strip_mined(1);
 
   // Add test to new "if" outside of loop
-  Node *bol   = unswitch_iff->in(1)->as_Bool();
+  IfNode* unswitch_iff = unswitch_iffs.at(0)->as_If();
+  BoolNode* bol = unswitch_iff->in(1)->as_Bool();
+  if (unswitch_iffs.size() > 1) {
+    // Flat array checks are used on array access to switch between
+    // a legacy object array access and a flat inline type array
+    // access. We want the performance impact on legacy accesses to be
+    // as small as possible so we make two copies of the loop: a fast
+    // one where all accesses are known to be legacy, a slow one where
+    // some accesses are to flat arrays. Flat array checks
+    // can be removed from the fast loop (true proj) but not from the
+    // slow loop (false proj) as it can have a mix of flat/legacy accesses.
+    assert(bol->_test._test == BoolTest::ne, "IfTrue proj must point to flat array");
+    bol = bol->clone()->as_Bool();
+    register_new_node(bol, entry);
+    FlatArrayCheckNode* cmp = bol->in(1)->clone()->as_FlatArrayCheck();
+    register_new_node(cmp, entry);
+    bol->set_req(1, cmp);
+    // Combine all checks into a single one that fails if one array is a flat array
+    assert(cmp->req() == 3, "unexpected number of inputs for FlatArrayCheck");
+    cmp->add_req_batch(C->top(), unswitch_iffs.size() - 1);
+    for (uint i = 0; i < unswitch_iffs.size(); i++) {
+      Node* array = unswitch_iffs.at(i)->in(1)->in(1)->in(FlatArrayCheckNode::ArrayOrKlass);
+      cmp->set_req(FlatArrayCheckNode::ArrayOrKlass + i, array);
+    }
+  }
+
   IfNode* iff = (unswitch_iff->Opcode() == Op_RangeCheck) ? new RangeCheckNode(entry, bol, unswitch_iff->_prob, unswitch_iff->_fcnt) :
-    new IfNode(entry, bol, unswitch_iff->_prob, unswitch_iff->_fcnt);
+      new IfNode(entry, bol, unswitch_iff->_prob, unswitch_iff->_fcnt);
   register_node(iff, outer_loop, entry, dom_depth(entry));
   IfProjNode* iffast = new IfTrueNode(iff);
   register_node(iffast, outer_loop, iff, dom_depth(iff));
   IfProjNode* ifslow = new IfFalseNode(iff);
   register_node(ifslow, outer_loop, iff, dom_depth(iff));
