8017065: C2 allows safepoint checks to leak into G1 pre-barriers

Summary: Make all raw loads strictly respect control dependencies, make sure RCE doesn't move raw loads, add verification of G1 pre-barriers.
Reviewed-by: kvn, roland

src/share/vm/opto/compile.cpp

@@ -848,6 +848,7 @@ Compile::Compile( ciEnv* ci_env, C2Compiler* compiler, ciMethod* target, int osr
   }
 #endif
 
+  NOT_PRODUCT( verify_barriers(); )
   // Now that we know the size of all the monitors we can add a fixed slot
   // for the original deopt pc.
 
@@ -3368,6 +3369,72 @@ void Compile::verify_graph_edges(bool no_dead_code) {
     }
   }
 }
+
+// Verify GC barriers consistency
+// Currently supported:
+// - G1 pre-barriers (see GraphKit::g1_write_barrier_pre())
+void Compile::verify_barriers() {
+  if (UseG1GC) {
+    // Verify G1 pre-barriers
+    const int marking_offset = in_bytes(JavaThread::satb_mark_queue_offset() + PtrQueue::byte_offset_of_active());
+
+    ResourceArea *area = Thread::current()->resource_area();
+    Unique_Node_List visited(area);
+    Node_List worklist(area);
+    // We're going to walk control flow backwards starting from the Root
+    worklist.push(_root);
+    while (worklist.size() > 0) {
+      Node* x = worklist.pop();
+      if (x == NULL || x == top()) continue;
+      if (visited.member(x)) {
+        continue;
+      } else {
+        visited.push(x);
+      }
+
+      if (x->is_Region()) {
+        for (uint i = 1; i < x->req(); i++) {
+          worklist.push(x->in(i));
+        }
+      } else {
+        worklist.push(x->in(0));
+        // We are looking for the pattern:
+        //                            /->ThreadLocal
+        // If->Bool->CmpI->LoadB->AddP->ConL(marking_offset)
+        //              \->ConI(0)
+        // We want to verify that the If and the LoadB have the same control
+        // See GraphKit::g1_write_barrier_pre()
+        if (x->is_If()) {
+          IfNode *iff = x->as_If();
+          if (iff->in(1)->is_Bool() && iff->in(1)->in(1)->is_Cmp()) {
+            CmpNode *cmp = iff->in(1)->in(1)->as_Cmp();
+            if (cmp->Opcode() == Op_CmpI && cmp->in(2)->is_Con() && cmp->in(2)->bottom_type()->is_int()->get_con() == 0
+                && cmp->in(1)->is_Load()) {
+              LoadNode* load = cmp->in(1)->as_Load();
+              if (load->Opcode() == Op_LoadB && load->in(2)->is_AddP() && load->in(2)->in(2)->Opcode() == Op_ThreadLocal
+                  && load->in(2)->in(3)->is_Con()
+                  && load->in(2)->in(3)->bottom_type()->is_intptr_t()->get_con() == marking_offset) {
+
+                Node* if_ctrl = iff->in(0);
+                Node* load_ctrl = load->in(0);
+
+                if (if_ctrl != load_ctrl) {
+                  // Skip possible CProj->NeverBranch in infinite loops
+                  if ((if_ctrl->is_Proj() && if_ctrl->Opcode() == Op_CProj)
+                      && (if_ctrl->in(0)->is_MultiBranch() && if_ctrl->in(0)->Opcode() == Op_NeverBranch)) {
+                    if_ctrl = if_ctrl->in(0)->in(0);
+                  }
+                }
+                assert(load_ctrl != NULL && if_ctrl == load_ctrl, "controls must match");
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+
 #endif
 
 // The Compile object keeps track of failure reasons separately from the ciEnv.

src/share/vm/opto/compile.hpp

@@ -1148,6 +1148,9 @@ class Compile : public Phase {
   // graph is strongly connected from root in both directions.
   void verify_graph_edges(bool no_dead_code = false) PRODUCT_RETURN;
 
+  // Verify GC barrier patterns
+  void verify_barriers() PRODUCT_RETURN;
+
   // End-of-run dumps.
   static void print_statistics() PRODUCT_RETURN;
 

src/share/vm/opto/loopTransform.cpp

@@ -1964,7 +1964,7 @@ void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
       // Find loads off the surviving projection; remove their control edge
       for (DUIterator_Fast imax, i = dp->fast_outs(imax); i < imax; i++) {
         Node* cd = dp->fast_out(i); // Control-dependent node
-        if( cd->is_Load() ) {   // Loads can now float around in the loop
+        if (cd->is_Load() && cd->depends_only_on_test()) {   // Loads can now float around in the loop
           // Allow the load to float around in the loop, or before it
           // but NOT before the pre-loop.
           _igvn.replace_input_of(cd, 0, ctrl); // ctrl, not NULL

src/share/vm/opto/memnode.hpp

@@ -204,6 +204,17 @@ public:
 protected:
   const Type* load_array_final_field(const TypeKlassPtr *tkls,
                                      ciKlass* klass) const;
+  // depends_only_on_test is almost always true, and needs to be almost always
+  // true to enable key hoisting & commoning optimizations.  However, for the
+  // special case of RawPtr loads from TLS top & end, and other loads performed by
+  // GC barriers, the control edge carries the dependence preventing hoisting past
+  // a Safepoint instead of the memory edge.  (An unfortunate consequence of having
+  // Safepoints not set Raw Memory; itself an unfortunate consequence of having Nodes
+  // which produce results (new raw memory state) inside of loops preventing all
+  // manner of other optimizations).  Basically, it's ugly but so is the alternative.
+  // See comment in macro.cpp, around line 125 expand_allocate_common().
+  virtual bool depends_only_on_test() const { return adr_type() != TypeRawPtr::BOTTOM; }
+
 };
 
 //------------------------------LoadBNode--------------------------------------
@@ -370,16 +381,6 @@ public:
   virtual uint ideal_reg() const { return Op_RegP; }
   virtual int store_Opcode() const { return Op_StoreP; }
   virtual BasicType memory_type() const { return T_ADDRESS; }
-  // depends_only_on_test is almost always true, and needs to be almost always
-  // true to enable key hoisting & commoning optimizations.  However, for the
-  // special case of RawPtr loads from TLS top & end, the control edge carries
-  // the dependence preventing hoisting past a Safepoint instead of the memory
-  // edge.  (An unfortunate consequence of having Safepoints not set Raw
-  // Memory; itself an unfortunate consequence of having Nodes which produce
-  // results (new raw memory state) inside of loops preventing all manner of
-  // other optimizations).  Basically, it's ugly but so is the alternative.
-  // See comment in macro.cpp, around line 125 expand_allocate_common().
-  virtual bool depends_only_on_test() const { return adr_type() != TypeRawPtr::BOTTOM; }
 };
 
 
@@ -393,16 +394,6 @@ public:
   virtual uint ideal_reg() const { return Op_RegN; }
   virtual int store_Opcode() const { return Op_StoreN; }
   virtual BasicType memory_type() const { return T_NARROWOOP; }
-  // depends_only_on_test is almost always true, and needs to be almost always
-  // true to enable key hoisting & commoning optimizations.  However, for the
-  // special case of RawPtr loads from TLS top & end, the control edge carries
-  // the dependence preventing hoisting past a Safepoint instead of the memory
-  // edge.  (An unfortunate consequence of having Safepoints not set Raw
-  // Memory; itself an unfortunate consequence of having Nodes which produce
-  // results (new raw memory state) inside of loops preventing all manner of
-  // other optimizations).  Basically, it's ugly but so is the alternative.
-  // See comment in macro.cpp, around line 125 expand_allocate_common().
-  virtual bool depends_only_on_test() const { return adr_type() != TypeRawPtr::BOTTOM; }
 };
 
 //------------------------------LoadKlassNode----------------------------------