8285558: IGV: scheduling crashes on control-unreachable CFG nodes

Reviewed-by: kvn, chagedorn

Author: robcasloz

src/utils/IdealGraphVisualizer/ServerCompiler/src/main/java/com/sun/hotspot/igv/servercompiler/ServerCompilerScheduler.java

@@ -53,6 +53,7 @@ private static class Node {
         public static final String WARNING_NOT_MARKED_WITH_BLOCK_START = "Region not marked with is_block_start";
         public static final String WARNING_CFG_AND_INPUT_TO_PHI = "CFG node is a phi input";
         public static final String WARNING_PHI_NON_DOMINATING_INPUTS = "Phi input that does not dominate the phi's input block";
+        public static final String WARNING_CONTROL_UNREACHABLE_CFG = "Control-unreachable CFG node";
 
         public InputNode inputNode;
         public Set<Node> succs = new HashSet<>();
@@ -327,20 +328,6 @@ public Collection<InputBlock> schedule(InputGraph graph) {
             schedulePinned();
             buildDominators();
             scheduleLatest();
-
-            InputBlock noBlock = null;
-            for (InputNode n : graph.getNodes()) {
-                if (graph.getBlock(n) == null) {
-                    if (noBlock == null) {
-                        noBlock = graph.addArtificialBlock();
-                        blocks.add(noBlock);
-                    }
-
-                    graph.setBlock(n, noBlock);
-                }
-                assert graph.getBlock(n) != null;
-            }
-
             scheduleLocal();
             check();
             reportWarnings();
@@ -632,6 +619,12 @@ public void schedulePinned() {
                     block = controlSuccs.get(ctrlIn).get(0).block;
                 }
             }
+            if (block == null) {
+                // This can happen for blockless CFG nodes that are not
+                // control-reachable from the root even after connecting orphans
+                // and widows (e.g. in disconnected control cycles).
+                continue;
+            }
             n.block = block;
             block.addNode(n.inputNode.getId());
         }
@@ -890,6 +883,9 @@ public void check() {
             if (isRegion(n) && !n.isBlockStart) {
                 n.addWarning(Node.WARNING_NOT_MARKED_WITH_BLOCK_START);
             }
+            if (n.isCFG && n.block == null) {
+                n.addWarning(Node.WARNING_CONTROL_UNREACHABLE_CFG);
+            }
             if (!isPhi(n)) {
                 continue;
             }