8360031: C2 compilation asserts in MemBarNode::remove

Reviewed-by: dlong, kvn, shade

Author: dafedafe

src/hotspot/share/opto/escape.cpp

@@ -201,7 +201,7 @@ bool ConnectionGraph::compute_escape() {
         if (!UseStoreStoreForCtor || n->req() > MemBarNode::Precedent) {
           storestore_worklist.append(n->as_MemBarStoreStore());
         }
-        break;
+        // If MemBarStoreStore has a precedent edge add it to the worklist (like MemBarRelease)
       case Op_MemBarRelease:
         if (n->req() > MemBarNode::Precedent) {
           record_for_optimizer(n);

src/hotspot/share/opto/memnode.cpp

@@ -4229,10 +4229,7 @@ MemBarNode* MemBarNode::make(Compile* C, int opcode, int atp, Node* pn) {
 }
 
 void MemBarNode::remove(PhaseIterGVN *igvn) {
-  if (outcnt() != 2) {
-    assert(Opcode() == Op_Initialize, "Only seen when there are no use of init memory");
-    assert(outcnt() == 1, "Only control then");
-  }
+  assert(outcnt() > 0 && outcnt() <= 2, "Only one or two out edges allowed");
   if (trailing_store() || trailing_load_store()) {
     MemBarNode* leading = leading_membar();
     if (leading != nullptr) {

test/hotspot/jtreg/compiler/c2/irTests/ConstructorBarriers.java

@@ -123,9 +123,12 @@ public VolatileVolatile(long i) {
     }
 
     long l = 42;
+    volatile Object global;
 
     @DontInline
-    public void consume(Object o) {}
+    public void consume(Object o) {
+        global = o;
+    }
 
     @Test
     @IR(counts = {IRNode.MEMBAR_STORESTORE, "1"})