From 43c91117c9a0afdb0ccc4e6e3fcd303850a558ec Mon Sep 17 00:00:00 2001
From: "Archie L. Cobbs" <archie.cobbs@gmail.com>
Date: Thu, 6 Nov 2025 10:54:59 -0600
Subject: [PATCH 1/2] Avoid lossy conversion warnings for 64 bit shift amounts.

---
 .../com/sun/tools/javac/comp/Attr.java        |  9 ++++-
 .../tools/javac/lint/AssignShift64Bits.java   | 36 +++++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 test/langtools/tools/javac/lint/AssignShift64Bits.java

diff --git a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java
index 617d8ca7077d1..666973d051ff2 100644
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java
@@ -3989,7 +3989,14 @@ public void visitAssignop(JCAssignOp tree) {
             chk.checkCastable(tree.rhs.pos(),
                               operator.type.getReturnType(),
                               owntype);
-            chk.checkLossOfPrecision(tree.rhs.pos(), operand, owntype);
+            switch (tree.getTag()) {
+            default -> {
+                chk.checkLossOfPrecision(tree.rhs.pos(), operand, owntype);
+            }
+            case SL_ASG, SR_ASG, USR_ASG -> {   // don't warn about shift amounts: we only use (at most) the lower 6 bits
+                break;
+            }
+            }
         }
         result = check(tree, owntype, KindSelector.VAL, resultInfo);
     }
diff --git a/test/langtools/tools/javac/lint/AssignShift64Bits.java b/test/langtools/tools/javac/lint/AssignShift64Bits.java
new file mode 100644
index 0000000000000..b761b0aeea195
--- /dev/null
+++ b/test/langtools/tools/javac/lint/AssignShift64Bits.java
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2025, 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 8371162
+ * @summary Verify no lossy conversion warning for 64 bit shift amount
+ * @compile -Xlint:lossy-conversions -Werror AssignShift64Bits.java
+ */
+
+public class AssignShift64Bits {
+    void m() {
+        int a = 1 << 1L;
+        a <<= 1L;
+        long b = 1 << 1L;
+        b <<= 1L;
+    }
+}

From e09ba44f760e060dad55eb1684aacdc3118a5b64 Mon Sep 17 00:00:00 2001
From: "Archie L. Cobbs" <archie.cobbs@gmail.com>
Date: Mon, 10 Nov 2025 14:52:57 -0600
Subject: [PATCH 2/2] Use cleaner switch statement syntax.

---
 .../share/classes/com/sun/tools/javac/comp/Attr.java      | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java
index 666973d051ff2..d2d704d165c72 100644
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java
@@ -3990,12 +3990,8 @@ public void visitAssignop(JCAssignOp tree) {
                               operator.type.getReturnType(),
                               owntype);
             switch (tree.getTag()) {
-            default -> {
-                chk.checkLossOfPrecision(tree.rhs.pos(), operand, owntype);
-            }
-            case SL_ASG, SR_ASG, USR_ASG -> {   // don't warn about shift amounts: we only use (at most) the lower 6 bits
-                break;
-            }
+            case SL_ASG, SR_ASG, USR_ASG -> { }     // we only use (at most) the lower 6 bits, so any integral type is OK
+            default -> chk.checkLossOfPrecision(tree.rhs.pos(), operand, owntype);
             }
         }
         result = check(tree, owntype, KindSelector.VAL, resultInfo);