8269230: C2: main loop in micro benchmark never executed

Co-authored-by: Maurizio Cimadamore <mcimadamore@openjdk.org>
Reviewed-by: kvn, iveresov

src/hotspot/share/opto/ifnode.cpp

@@ -1011,6 +1011,33 @@ bool IfNode::fold_compares_helper(ProjNode* proj, ProjNode* success, ProjNode* f
       adjusted_lim = igvn->transform(new SubINode(hi, lo));
     }
     hook->destruct(igvn);
+
+    int lo = igvn->type(adjusted_lim)->is_int()->_lo;
+    if (lo < 0) {
+      // If range check elimination applies to this comparison, it includes code to protect from overflows that may
+      // cause the main loop to be skipped entirely. Delay this transformation.
+      // Example:
+      // for (int i = 0; i < limit; i++) {
+      //   if (i < max_jint && i > min_jint) {...
+      // }
+      // Comparisons folded as:
+      // i - min_jint - 1 <u -2
+      // when RC applies, main loop limit becomes:
+      // min(limit, max(-2 + min_jint + 1, min_jint))
+      // = min(limit, min_jint)
+      // = min_jint
+      if (!igvn->C->post_loop_opts_phase()) {
+        if (adjusted_val->outcnt() == 0) {
+          igvn->remove_dead_node(adjusted_val);
+        }
+        if (adjusted_lim->outcnt() == 0) {
+          igvn->remove_dead_node(adjusted_lim);
+        }
+        igvn->C->record_for_post_loop_opts_igvn(this);
+        return false;
+      }
+    }
+
     Node* newcmp = igvn->transform(new CmpUNode(adjusted_val, adjusted_lim));
     Node* newbool = igvn->transform(new BoolNode(newcmp, cond));
 

test/micro/org/openjdk/bench/jdk/incubator/foreign/TestLoadBytes.java

@@ -0,0 +1,137 @@
+/*
+ * Copyright (c) 2021, 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.
+ */
+
+package org.openjdk.bench.jdk.incubator.foreign;
+
+import jdk.incubator.foreign.CLinker;
+import jdk.incubator.foreign.MemoryAccess;
+import jdk.incubator.foreign.MemoryAddress;
+import jdk.incubator.foreign.MemorySegment;
+import jdk.incubator.foreign.ResourceScope;
+import jdk.incubator.vector.ByteVector;
+import jdk.incubator.vector.IntVector;
+import jdk.incubator.vector.VectorSpecies;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.CompilerControl;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@State(org.openjdk.jmh.annotations.Scope.Thread)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Fork(value = 1, jvmArgsAppend = {
+        "--add-modules=jdk.incubator.foreign",
+        "-Dforeign.restricted=permit",
+        "--enable-native-access", "ALL-UNNAMED"})
+public class TestLoadBytes {
+    @Param("1024")
+    private int size;
+
+    private byte[] srcArray;
+    private ByteBuffer srcBufferNative;
+    private MemorySegment srcSegmentImplicit;
+
+    @Setup
+    public void setup() {
+        srcArray = new byte[size];
+        for (int i = 0; i < srcArray.length; i++) {
+            srcArray[i] = (byte) i;
+        }
+
+        srcBufferNative = ByteBuffer.allocateDirect(size);
+        srcSegmentImplicit = MemorySegment.allocateNative(size, ResourceScope.newImplicitScope());
+    }
+
+    @Benchmark
+    public int arrayScalar() {
+        int size = 0;
+        for (int i = 0; i < srcArray.length; i ++) {
+            var v = srcArray[i];
+            size += v;
+        }
+        return size;
+    }
+
+    @Benchmark
+    public int arrayScalarConst() {
+        int size = 0;
+        for (int i = 0; i < 1024; i ++) {
+            var v = srcArray[i];
+            size += v;
+        }
+        return size;
+    }
+
+    @Benchmark
+    public int bufferNativeScalar() {
+        int size = 0;
+        for (int i = 0; i < srcArray.length; i++) {
+            var v = srcBufferNative.get(i);
+            size += v;
+        }
+        return size;
+    }
+
+    @Benchmark
+    public int bufferNativeScalarConst() {
+        int size = 0;
+        for (int i = 0; i < 1024; i++) {
+            var v = srcBufferNative.get(i);
+            size += v;
+        }
+        return size;
+    }
+
+    @Benchmark
+    public int segmentNativeScalar() {
+        int size = 0;
+        for (int i = 0; i < srcArray.length; i++) {
+            var v = MemoryAccess.getByteAtOffset(srcSegmentImplicit, i);
+            size += v;
+        }
+        return size;
+    }
+
+    @Benchmark
+    public int segmentNativeScalarConst() {
+        int size = 0;
+        for (int i = 0; i < 1024; i++) {
+            var v = MemoryAccess.getByteAtOffset(srcSegmentImplicit, i);
+            size += v;
+        }
+        return size;
+    }
+}