8271254: javac generates unreachable code when using empty semicolon statement

Backport-of: fe89dd3b0d47807c7dbfe24d17f6aca152fc8908

Author: lgxbslgx

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Gen.java

@@ -1510,8 +1510,8 @@ void afterBody() {
     //where
         /** Generate code for a try or synchronized statement
          *  @param body      The body of the try or synchronized statement.
-         *  @param catchers  The lis of catch clauses.
-         *  @param env       the environment current for the body.
+         *  @param catchers  The list of catch clauses.
+         *  @param env       The current environment of the body.
          */
         void genTry(JCTree body, List<JCCatch> catchers, Env<GenContext> env) {
             int limit = code.nextreg;
@@ -1523,7 +1523,13 @@ void genTry(JCTree body, List<JCCatch> catchers, Env<GenContext> env) {
             code.statBegin(TreeInfo.endPos(body));
             genFinalizer(env);
             code.statBegin(TreeInfo.endPos(env.tree));
-            Chain exitChain = code.branch(goto_);
+            Chain exitChain;
+            boolean actualTry = env.tree.hasTag(TRY);
+            if (startpc == endpc && actualTry) {
+                exitChain = code.branch(dontgoto);
+            } else {
+                exitChain = code.branch(goto_);
+            }
             endFinalizerGap(env);
             env.info.finalize.afterBody();
             boolean hasFinalizer =
@@ -1541,7 +1547,7 @@ void genTry(JCTree body, List<JCCatch> catchers, Env<GenContext> env) {
                 }
                 endFinalizerGap(env);
             }
-            if (hasFinalizer) {
+            if (hasFinalizer && (startpc != endpc || !actualTry)) {
                 // Create a new register segment to avoid allocating
                 // the same variables in finalizers and other statements.
                 code.newRegSegment();

test/langtools/tools/javac/T8022186/DeadCodeGeneratedForEmptyTryTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 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
@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 8022186
+ * @bug 8022186 8271254
  * @summary javac generates dead code if a try with an empty body has a finalizer
  * @modules jdk.jdeps/com.sun.tools.classfile
  *          jdk.compiler/com.sun.tools.javac.util
@@ -53,15 +53,18 @@ public static void main(String[] args) throws Exception {
     }
 
     void run() throws Exception {
-        checkClassFile(Paths.get(System.getProperty("test.classes"),
-                this.getClass().getName() + "$Test.class"));
+        for (int i = 1; i <= 8; i++) {
+            checkClassFile(Paths.get(System.getProperty("test.classes"),
+                    this.getClass().getName() + "$Test" + i + ".class"));
+        }
     }
 
     int utf8Index;
     int numberOfRefToStr = 0;
     ConstantPool constantPool;
 
     void checkClassFile(final Path path) throws Exception {
+        numberOfRefToStr = 0;
         ClassFile classFile = ClassFile.read(
                 new BufferedInputStream(Files.newInputStream(path)));
         constantPool = classFile.constant_pool;
@@ -155,9 +158,92 @@ public Void visitUnknown(Instruction instr, Void p) {
 
     }
 
-    public class Test {
+    public class Test1 {
+        void methodToLookFor() {
+            try {
+                // empty intentionally
+            } finally {
+                System.out.println("STR_TO_LOOK_FOR");
+            }
+        }
+    }
+
+    public class Test2 {
+        void methodToLookFor() {
+            try {
+                // empty intentionally
+            } catch (Exception e) {
+                System.out.println("EXCEPTION");
+            } finally {
+                System.out.println("STR_TO_LOOK_FOR");
+            }
+        }
+    }
+
+    public class Test3 {
+        void methodToLookFor() {
+            try {
+                ;  // skip statement intentionally
+            } finally {
+                System.out.println("STR_TO_LOOK_FOR");
+            }
+        }
+    }
+
+    public class Test4 {
+        void methodToLookFor() {
+            try {
+                ;  // skip statement intentionally
+            } catch (Exception e) {
+                System.out.println("EXCEPTION");
+            } finally {
+                System.out.println("STR_TO_LOOK_FOR");
+            }
+        }
+    }
+
+    public class Test5 {
+        void methodToLookFor() {
+            try {
+                // empty try statement
+                try { } finally { }
+            } finally {
+                System.out.println("STR_TO_LOOK_FOR");
+            }
+        }
+    }
+
+    public class Test6 {
+        void methodToLookFor() {
+            try {
+                // empty try statement
+                try { } catch (Exception e) { } finally { }
+            } catch (Exception e) {
+                System.out.println("EXCEPTION");
+            } finally {
+                System.out.println("STR_TO_LOOK_FOR");
+            }
+        }
+    }
+
+    public class Test7 {
+        void methodToLookFor() {
+            try {
+                // empty try statement with skip statement
+                try { ; } finally { }
+            } finally {
+                System.out.println("STR_TO_LOOK_FOR");
+            }
+        }
+    }
+
+    public class Test8 {
         void methodToLookFor() {
             try {
+                // empty try statement with skip statement
+                try { ; } catch (Exception e) { } finally { }
+            } catch (Exception e) {
+                System.out.println("EXCEPTION");
             } finally {
                 System.out.println("STR_TO_LOOK_FOR");
             }