8278471: Remove unreached rules in AddNode::IdealIL

src/hotspot/share/opto/addnode.cpp

@@ -302,16 +302,6 @@ Node* AddNode::IdealIL(PhaseGVN* phase, bool can_reshape, BasicType bt) {
       assert(in1->in(1) != this && in2->in(1) != this,"dead loop in AddINode::Ideal/AddLNode::Ideal");
       return AddNode::make(in1->in(1), in2->in(1), bt);
     }
-    // Convert "(a-b)+(b-c)" into "(a-c)"
-    if (op2 == Op_Sub(bt) && in1->in(2) == in2->in(1)) {
-      assert(in1->in(1) != this && in2->in(2) != this,"dead loop in AddINode::Ideal/AddLNode::Ideal");
-      return SubNode::make(in1->in(1), in2->in(2), bt);
-    }
-    // Convert "(a-b)+(c-a)" into "(c-b)"
-    if (op2 == Op_Sub(bt) && in1->in(1) == in2->in(2)) {
-      assert(in1->in(2) != this && in2->in(1) != this,"dead loop in AddINode::Ideal/AddLNode::Ideal");
-      return SubNode::make(in2->in(1), in1->in(2), bt);
-    }
   }
 
   // Convert "x+(0-y)" into "(x-y)"

src/hotspot/share/opto/subnode.cpp

@@ -435,6 +435,14 @@ Node *SubLNode::Ideal(PhaseGVN *phase, bool can_reshape) {
   if( op1 == Op_AddL && op2 == Op_AddL && in1->in(2) == in2->in(2) )
     return new SubLNode( in1->in(1), in2->in(1) );
 
+  // Convert "(A+X) - (X+B)" into "A - B"
+  if( op1 == Op_AddL && op2 == Op_AddL && in1->in(2) == in2->in(1) )
+    return new SubLNode( in1->in(1), in2->in(2) );
+
+  // Convert "(X+A) - (B+X)" into "A - B"
+  if( op1 == Op_AddL && op2 == Op_AddL && in1->in(1) == in2->in(2) )
+    return new SubLNode( in1->in(2), in2->in(1) );
+
   // Convert "A-(B-C)" into (A+C)-B"
   if( op2 == Op_SubL && in2->outcnt() == 1) {
     Node *add1 = phase->transform( new AddLNode( in1, in2->in(2) ) );

test/hotspot/jtreg/compiler/c2/irTests/TestSpecialCasesOf_AMinusB_Plus_CMinusD_InAddIdeal.java

@@ -0,0 +1,76 @@
+/*
+ * 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 compiler.c2.irTests;
+
+import jdk.test.lib.Asserts;
+import compiler.lib.ir_framework.*;
+
+/*
+ * @test
+ * @bug 8278471
+ * @summary Remove unreached rules in AddNode::IdealIL
+ * @library /test/lib /
+ * @run driver compiler.c2.irTests.TestSpecialCasesOf_AMinusB_Plus_CMinusD_InAddIdeal
+ */
+/* Test conversion from (a - b) + (b - c) to (a - c) and conversion
+ * from (a - b) + (c - a) to (c - b) have really happened so we can
+ * safely remove both. */
+public class TestSpecialCasesOf_AMinusB_Plus_CMinusD_InAddIdeal {
+
+    public static void main(String[] args) {
+        TestFramework.run();
+    }
+
+    @Test
+    @Arguments({Argument.RANDOM_ONCE, Argument.RANDOM_ONCE, Argument.RANDOM_ONCE})
+    @IR(failOn = {IRNode.ADD_I})
+    @IR(counts = {IRNode.SUB_I, "1"})
+    public int test1Int(int a, int b, int c) {
+        return (a - b) + (b - c); // transformed to a - c rather than (a + b) - (b + c)
+    }
+
+    @Test
+    @Arguments({Argument.RANDOM_ONCE, Argument.RANDOM_ONCE, Argument.RANDOM_ONCE})
+    @IR(failOn = {IRNode.ADD_L})
+    @IR(counts = {IRNode.SUB_L, "1"})
+    public long test1Long(long a, long b, long c) {
+        return (a - b) + (b - c); // transformed to a - c rather than (a + b) - (b + c)
+    }
+
+    @Test
+    @Arguments({Argument.RANDOM_ONCE, Argument.RANDOM_ONCE, Argument.RANDOM_ONCE})
+    @IR(failOn = {IRNode.ADD_I})
+    @IR(counts = {IRNode.SUB_I, "1"})
+    public int test2Int(int b, int a, int c) { // make sure inputs sorted
+        return (a - b) + (c - a); // transformed to c - b rather than (a + c) - (b + a)
+    }
+
+    @Test
+    @Arguments({Argument.RANDOM_ONCE, Argument.RANDOM_ONCE, Argument.RANDOM_ONCE})
+    @IR(failOn = {IRNode.ADD_L})
+    @IR(counts = {IRNode.SUB_L, "1"})
+    public long test2Long(long b, long a, long c) { // make sure inputs sorted
+        return (a - b) + (c - a); // transformed to return c - b rather than (a + c) - (b + a)
+    }
+}

test/hotspot/jtreg/compiler/lib/ir_framework/IRNode.java

@@ -139,6 +139,8 @@ public class IRNode {
     public static final String LSHIFT_L = START + "LShiftL" + MID + END;
     public static final String ADD_I = START + "AddI" + MID + END;
     public static final String ADD_L = START + "AddL" + MID + END;
+    public static final String SUB_I = START + "SubI" + MID + END;
+    public static final String SUB_L = START + "SubL" + MID + END;
     public static final String CONV_I2L = START + "ConvI2L" + MID + END;
 
     /**