src/hotspot/share/opto/macro.cpp

@@ -346,10 +346,11 @@
     bt = T_OBJECT;
     type = ftype->make_oopptr();
   }
   Node* res = NULL;
   if (ac->is_clonebasic()) {
+    assert(ac->in(ArrayCopyNode::Src) != ac->in(ArrayCopyNode::Dest), "clone source equals destination");
     Node* base = ac->in(ArrayCopyNode::Src)->in(AddPNode::Base);
     Node* adr = _igvn.transform(new AddPNode(base, base, MakeConX(offset)));
     const TypePtr* adr_type = _igvn.type(base)->is_ptr()->add_offset(offset);
     res = LoadNode::make(_igvn, ctl, mem, adr, adr_type, type, bt, MemNode::unordered, LoadNode::UnknownControl);
   } else {

@@ -364,10 +365,14 @@
 
       Node* off = _igvn.transform(new AddXNode(MakeConX(offset), diff));
       Node* base = ac->in(ArrayCopyNode::Src);
       Node* adr = _igvn.transform(new AddPNode(base, base, off));
       const TypePtr* adr_type = _igvn.type(base)->is_ptr()->add_offset(offset);
+      if (ac->in(ArrayCopyNode::Src) == ac->in(ArrayCopyNode::Dest)) {
+        // Don't emit a new load from src if src == dst but try to get the value from memory instead
+        return value_from_mem(ac->in(TypeFunc::Memory), ctl, ft, ftype, adr_type->isa_oopptr(), alloc);
+      }
       res = LoadNode::make(_igvn, ctl, mem, adr, adr_type, type, bt, MemNode::unordered, LoadNode::UnknownControl);
     }
   }
   if (res != NULL) {
     res = _igvn.transform(res);

@@ -495,11 +500,10 @@
   Node *alloc_ctrl = alloc->in(TypeFunc::Control);
   Node *alloc_mem = alloc->in(TypeFunc::Memory);
   Arena *a = Thread::current()->resource_area();
   VectorSet visited(a);
 
-
   bool done = sfpt_mem == alloc_mem;
   Node *mem = sfpt_mem;
   while (!done) {
     if (visited.test_set(mem->_idx)) {
       return NULL;  // found a loop, give up