src/share/vm/opto/ifg.cpp

rev 5451 : 8065618: C2 RA incorrectly removes kill projections
Summary: Don't remove KILL projections if their "defining" nodes have SCMemProj projection (memory side effects).
Reviewed-by: iveresov, roland
rev 5452 : 8066649: 8u backport for 8065618 is incorrect
Summary: The new code in 8u backport should guard the execution of the following code instead of return.
Reviewed-by: iveresov

*** 569,588 ****
--- 569,608 ----
          if( !liveout.member(r) && n->Opcode() != Op_SafePoint ) {
            Node *def = n->in(0);
            if( !n->is_Proj() ||
                // Could also be a flags-projection of a dead ADD or such.
                (n2lidx(def) && !liveout.member(n2lidx(def)) ) ) {
+             bool remove = true;
+             if (n->is_MachProj()) {
+               // Don't remove KILL projections if their "defining" nodes have
+               // memory effects (have SCMemProj projection node) -
+               // they are not dead even when their result is not used.
+               // For example, compareAndSwapL (and other CAS) and EncodeISOArray nodes.
+               // The method add_input_to_liveout() keeps such nodes alive (put them on liveout list)
+               // when it sees SCMemProj node in a block. Unfortunately SCMemProj node could be placed
+               // in block in such order that KILL MachProj nodes are processed first.
+               uint cnt = def->outcnt();
+               for (uint i = 0; i < cnt; i++) {
+                 Node* proj = def->raw_out(i);
+                 if (proj->Opcode() == Op_SCMemProj) {
+                   remove = false;
+                   break;
+                 }
+               }
+             }
+             if (remove) {
                b->_nodes.remove(j - 1);
                if( lrgs(r)._def == n ) lrgs(r)._def = 0;
                n->disconnect_inputs(NULL, C);
                _cfg._bbs.map(n->_idx,NULL);
                n->replace_by(C->top());
                // Since yanking a Node from block, high pressure moves up one
                hrp_index[0]--;
                hrp_index[1]--;
                continue;
              }
+           }
  
            // Fat-projections kill many registers which cannot be used to
            // hold live ranges.
            if( lrgs(r)._fat_proj ) {
              // Count the int-only registers