diff --git a/src/hotspot/share/opto/block.cpp b/src/hotspot/share/opto/block.cpp
index f67f92de360..811e4002cdc 100644
--- a/src/hotspot/share/opto/block.cpp
+++ b/src/hotspot/share/opto/block.cpp
@@ -151,6 +151,10 @@ bool Block::contains(const Node *n) const {
return _nodes.contains(n);
}
+bool Block::is_trivially_unreachable() const {
+ return num_preds() <= 1 && !head()->is_Root() && !head()->is_Start();
+}
+
// Return empty status of a block. Empty blocks contain only the head, other
// ideal nodes, and an optional trailing goto.
int Block::is_Empty() const {
@@ -170,7 +174,7 @@ int Block::is_Empty() const {
}
// Unreachable blocks are considered empty
- if (num_preds() <= 1) {
+ if (is_trivially_unreachable()) {
return success_result;
}
@@ -608,19 +612,6 @@ void PhaseCFG::convert_NeverBranch_to_Goto(Block *b) {
for (int k = 1; dead->get_node(k)->is_Phi(); k++) {
dead->get_node(k)->del_req(j);
}
- // If the fake exit block becomes unreachable, remove it from the block list.
- if (dead->num_preds() == 1) {
- for (uint i = 0; i < number_of_blocks(); i++) {
- Block* block = get_block(i);
- if (block == dead) {
- _blocks.remove(i);
- } else if (block->_pre_order > dead->_pre_order) {
- // Enforce contiguous pre-order indices (assumed by PhaseBlockLayout).
- block->_pre_order--;
- }
- }
- _number_of_blocks--;
- }
}
// Helper function to move block bx to the slot following b_index. Return
@@ -957,6 +948,46 @@ void PhaseCFG::fixup_flow() {
} // End of for all blocks
}
+void PhaseCFG::remove_unreachable_blocks() {
+ ResourceMark rm;
+ Block_List unreachable;
+ // Initialize worklist of unreachable blocks to be removed.
+ for (uint i = 0; i < number_of_blocks(); i++) {
+ Block* block = get_block(i);
+ assert(block->_pre_order == i, "Block::pre_order does not match block index");
+ if (block->is_trivially_unreachable()) {
+ unreachable.push(block);
+ }
+ }
+ // Now remove all blocks that are transitively unreachable.
+ while (unreachable.size() > 0) {
+ Block* dead = unreachable.pop();
+ // When this code runs (after PhaseCFG::fixup_flow()), Block::_pre_order
+ // does not contain pre-order but block-list indices. Ensure they stay
+ // contiguous by decrementing _pre_order for all elements after 'dead'.
+ // Block::_rpo does not contain valid reverse post-order indices anymore
+ // (they are invalidated by block insertions in PhaseCFG::fixup_flow()),
+ // so there is no need to update them.
+ for (uint i = dead->_pre_order + 1; i < number_of_blocks(); i++) {
+ get_block(i)->_pre_order--;
+ }
+ _blocks.remove(dead->_pre_order);
+ _number_of_blocks--;
+ // Update the successors' predecessor list and push new unreachable blocks.
+ for (uint i = 0; i < dead->_num_succs; i++) {
+ Block* succ = dead->_succs[i];
+ Node* head = succ->head();
+ for (int j = head->req() - 1; j >= 1; j--) {
+ if (get_block_for_node(head->in(j)) == dead) {
+ head->del_req(j);
+ }
+ }
+ if (succ->is_trivially_unreachable()) {
+ unreachable.push(succ);
+ }
+ }
+ }
+}
// postalloc_expand: Expand nodes after register allocation.
//
diff --git a/src/hotspot/share/opto/block.hpp b/src/hotspot/share/opto/block.hpp
index 093ba1bd1ff..060b4963656 100644
--- a/src/hotspot/share/opto/block.hpp
+++ b/src/hotspot/share/opto/block.hpp
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2022, Oracle and/or its affiliates. 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
@@ -321,6 +321,9 @@ class Block : public CFGElement {
// Check whether the node is in the block.
bool contains (const Node *n) const;
+ // Whether the block is not root-like and does not have any predecessors.
+ bool is_trivially_unreachable() const;
+
// Return the empty status of a block
enum { not_empty, empty_with_goto, completely_empty };
int is_Empty() const;
@@ -604,6 +607,10 @@ class PhaseCFG : public Phase {
void remove_empty_blocks();
Block *fixup_trap_based_check(Node *branch, Block *block, int block_pos, Block *bnext);
void fixup_flow();
+ // Remove all blocks that are transitively unreachable. Such blocks can be
+ // found e.g. after PhaseCFG::convert_NeverBranch_to_Goto(). This function
+ // assumes post-fixup_flow() block indices (Block::_pre_order, Block::_rpo).
+ void remove_unreachable_blocks();
// Insert a node into a block at index and map the node to the block
void insert(Block *b, uint idx, Node *n) {
diff --git a/src/hotspot/share/opto/compile.cpp b/src/hotspot/share/opto/compile.cpp
index 060ed341fdb..b22626bcff2 100644
--- a/src/hotspot/share/opto/compile.cpp
+++ b/src/hotspot/share/opto/compile.cpp
@@ -2756,6 +2756,7 @@ void Compile::Code_Gen() {
cfg.set_loop_alignment();
}
cfg.fixup_flow();
+ cfg.remove_unreachable_blocks();
}
// Apply peephole optimizations
diff --git a/test/hotspot/jtreg/compiler/loopopts/TestMultipleInfiniteLoops.java b/test/hotspot/jtreg/compiler/loopopts/TestMultipleInfiniteLoops.java
new file mode 100644
index 00000000000..e42e76c7e7f
--- /dev/null
+++ b/test/hotspot/jtreg/compiler/loopopts/TestMultipleInfiniteLoops.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2022, Oracle and/or its affiliates. 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 8292660
+ * @summary Test that blocks made unreachable after processing multiple infinite
+ * loops in the block ordering phase are removed correctly.
+ *
+ * @run main/othervm -Xcomp -XX:CompileOnly=compiler.loopopts.TestMultipleInfiniteLoops::test
+ * compiler.loopopts.TestMultipleInfiniteLoops
+ */
+
+package compiler.loopopts;
+
+public class TestMultipleInfiniteLoops {
+
+ static int foo;
+
+ static void test() {
+ int i = 5, j;
+ while (i > 0) {
+ for (j = i; 1 > j; ) {
+ switch (i) {
+ case 4:
+ foo = j;
+ }
+ }
+ i++;
+ }
+ }
+
+ public static void main(String[] args) {
+ test();
+ }
+}