8263303: C2 compilation fails with assert(found_sfpt) failed: no node in loop that's not input to safepoint

Reviewed-by: roland
Backport-of: d4377af

Author: TheRealMDoerr

src/hotspot/share/opto/loopnode.cpp

@@ -978,33 +978,6 @@ void LoopNode::verify_strip_mined(int expect_skeleton) const {
     Node* sfpt = outer_le->in(0);
     assert(sfpt->Opcode() == Op_SafePoint, "where's the safepoint?");
     Node* inner_out = sfpt->in(0);
-    if (inner_out->outcnt() != 1) {
-      ResourceMark rm;
-      Unique_Node_List wq;
-
-      for (DUIterator_Fast imax, i = inner_out->fast_outs(imax); i < imax; i++) {
-        Node* u = inner_out->fast_out(i);
-        if (u == sfpt) {
-          continue;
-        }
-        wq.clear();
-        wq.push(u);
-        bool found_sfpt = false;
-        for (uint next = 0; next < wq.size() && !found_sfpt; next++) {
-          Node *n = wq.at(next);
-          for (DUIterator_Fast imax, i = n->fast_outs(imax); i < imax && !found_sfpt; i++) {
-            Node* u = n->fast_out(i);
-            if (u == sfpt) {
-              found_sfpt = true;
-            }
-            if (!u->is_CFG()) {
-              wq.push(u);
-            }
-          }
-        }
-        assert(found_sfpt, "no node in loop that's not input to safepoint");
-      }
-    }
     CountedLoopEndNode* cle = inner_out->in(0)->as_CountedLoopEnd();
     assert(cle == inner->loopexit_or_null(), "mismatch");
     bool has_skeleton = outer_le->in(1)->bottom_type()->singleton() && outer_le->in(1)->bottom_type()->is_int()->get_con() == 0;

src/hotspot/share/opto/loopopts.cpp

@@ -1851,7 +1851,7 @@ static void clone_outer_loop_helper(Node* n, const IdealLoopTree *loop, const Id
     Node* u = n->fast_out(j);
     assert(check_old_new || old_new[u->_idx] == NULL, "shouldn't have been cloned");
     if (!u->is_CFG() && (!check_old_new || old_new[u->_idx] == NULL)) {
-      Node* c = phase->get_ctrl(u);
+      Node* c = u->in(0) != NULL ? u->in(0) : phase->get_ctrl(u);
       IdealLoopTree* u_loop = phase->get_loop(c);
       assert(!loop->is_member(u_loop), "can be in outer loop or out of both loops only");
       if (outer_loop->is_member(u_loop)) {
@@ -1974,11 +1974,20 @@ void PhaseIdealLoop::clone_outer_loop(LoopNode* head, CloneLoopMode mode, IdealL
       Node* old = extra_data_nodes.at(i);
       clone_outer_loop_helper(old, loop, outer_loop, old_new, wq, this, true);
     }
+
+    Node* inner_out = sfpt->in(0);
+    if (inner_out->outcnt() > 1) {
+      clone_outer_loop_helper(inner_out, loop, outer_loop, old_new, wq, this, true);
+    }
+
     Node* new_ctrl = cl->outer_loop_exit();
     assert(get_loop(new_ctrl) != outer_loop, "must be out of the loop nest");
     for (uint i = 0; i < wq.size(); i++) {
       Node* n = wq.at(i);
       set_ctrl(n, new_ctrl);
+      if (n->in(0) != NULL) {
+        _igvn.replace_input_of(n, 0, new_ctrl);
+      }
       clone_outer_loop_helper(n, loop, outer_loop, old_new, wq, this, false);
     }
   } else {

test/hotspot/jtreg/compiler/loopstripmining/TestPinnedUseInOuterLSMUnusedBySfpt.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2021, Red Hat, Inc. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8263303
+ * @summary C2 compilation fails with assert(found_sfpt) failed: no node in loop that's not input to safepoint
+ *
+ * @run main/othervm -XX:-BackgroundCompilation -XX:LoopUnrollLimit=0 TestPinnedUseInOuterLSMUnusedBySfpt
+ *
+ */
+
+public class TestPinnedUseInOuterLSMUnusedBySfpt {
+    public static void main(String[] args) {
+        int[] array = new int[10000];
+        for (int i = 0; i < 20_000; i++) {
+            test(100, array, 42);
+            test(100, array, 0);
+        }
+    }
+
+    private static float test(int stop, int[] array, int val) {
+        if (array == null) {
+        }
+        int j;
+        for (j = 0; j < 10; j++) {
+
+        }
+        int i;
+        int v = 0;
+        float f = 1;
+        for (i = 0; i < 10000; i++) {
+            if ((j - 10) * i + val == 42) {
+                f *= 2;
+            } else {
+                f *= 3;
+            }
+            v = (j - 10) * array[i];
+            if (i % 10001 != i) {
+                return v;
+            }
+        }
+        return v + array[i-1] + f;
+    }
+}