rewrite Long.compare(long, long) to JVM instruction lcmp, so that devices with

API level below 19 can still use Long.compare(long, long)

RELNOTES: n/a

--
PiperOrigin-RevId: 151040972
MOS_MIGRATED_REVID=151040972

3 files changed, 80 insertions, 9 deletions

diff --git a/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java b/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java
index 1711f57a99..7be39052bd 100644
--- a/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java
+++ b/src/tools/android/java/com/google/devtools/build/android/desugar/Desugar.java
@@ -101,6 +101,14 @@ class Desugar {
     public boolean onlyDesugarJavac9ForLint;
 
     @Option(
+      name = "rewrite_calls_to_long_compare",
+      defaultValue = "true",
+      help = "rewrite calls to Long.compare(long, long) to the JVM instruction lcmp",
+      category = "misc"
+    )
+    public boolean enableRewritingOfLongCompare;
+
+    @Option(
       name = "output",
       allowMultiple = true,
       defaultValue = "",
@@ -264,7 +272,10 @@ class Desugar {
                 }
 
                 if (!allowCallsToObjectsNonNull) {
-                  visitor = new ObjectsRequireNonNullMethodInliner(visitor);
+                  visitor = new ObjectsRequireNonNullMethodRewriter(visitor);
+                }
+                if (options.enableRewritingOfLongCompare) {
+                  visitor = new LongCompareMethodRewriter(visitor);
                 }
                 reader.accept(visitor, 0);
 
@@ -313,7 +324,10 @@ class Desugar {
               if (!allowCallsToObjectsNonNull) {
                 // Not sure whether there will be implicit null check emitted by javac, so we rerun
                 // the inliner again
-                visitor = new ObjectsRequireNonNullMethodInliner(visitor);
+                visitor = new ObjectsRequireNonNullMethodRewriter(visitor);
+              }
+              if (options.enableRewritingOfLongCompare) {
+                visitor = new LongCompareMethodRewriter(visitor);
               }
               reader.accept(visitor, 0);
               String filename =
@@ -321,10 +335,10 @@ class Desugar {
               outputFileProvider.write(filename, writer.toByteArray());
             }
           }
-
-          Map<Path, LambdaInfo> leftBehind = lambdas.drain();
-          checkState(leftBehind.isEmpty(), "Didn't process %s", leftBehind);
         }
+
+        Map<Path, LambdaInfo> leftBehind = lambdas.drain();
+        checkState(leftBehind.isEmpty(), "Didn't process %s", leftBehind);
       }
     }
   }
diff --git a/src/tools/android/java/com/google/devtools/build/android/desugar/LongCompareMethodRewriter.java b/src/tools/android/java/com/google/devtools/build/android/desugar/LongCompareMethodRewriter.java
new file mode 100644
index 0000000000..23d7a0d0b1
--- /dev/null
+++ b/src/tools/android/java/com/google/devtools/build/android/desugar/LongCompareMethodRewriter.java
@@ -0,0 +1,58 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.android.desugar;
+
+import static org.objectweb.asm.Opcodes.ASM5;
+import static org.objectweb.asm.Opcodes.INVOKESTATIC;
+import static org.objectweb.asm.Opcodes.LCMP;
+
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.MethodVisitor;
+
+/**
+ * This class rewrites any call to Long.compare with the JVM instruction lcmp that is semantically
+ * equivalent to Long.compare.
+ */
+public class LongCompareMethodRewriter extends ClassVisitor {
+
+  public LongCompareMethodRewriter(ClassVisitor cv) {
+    super(ASM5, cv);
+  }
+
+  @Override
+  public MethodVisitor visitMethod(
+      int access, String name, String desc, String signature, String[] exceptions) {
+    MethodVisitor visitor = super.cv.visitMethod(access, name, desc, signature, exceptions);
+    return visitor == null ? visitor : new LongCompareMethodVisitor(visitor);
+  }
+
+  private static class LongCompareMethodVisitor extends MethodVisitor {
+
+    public LongCompareMethodVisitor(MethodVisitor visitor) {
+      super(ASM5, visitor);
+    }
+
+    @Override
+    public void visitMethodInsn(int opcode, String owner, String name, String desc, boolean itf) {
+      if (opcode != INVOKESTATIC
+          || !owner.equals("java/lang/Long")
+          || !name.equals("compare")
+          || !desc.equals("(JJ)I")) {
+        super.visitMethodInsn(opcode, owner, name, desc, itf);
+        return;
+      }
+      super.visitInsn(LCMP);
+    }
+  }
+}
diff --git a/src/tools/android/java/com/google/devtools/build/android/desugar/ObjectsRequireNonNullMethodInliner.java b/src/tools/android/java/com/google/devtools/build/android/desugar/ObjectsRequireNonNullMethodRewriter.java
index e56cfe1d1b..5ce0bee6a1 100644
--- a/src/tools/android/java/com/google/devtools/build/android/desugar/ObjectsRequireNonNullMethodInliner.java
+++ b/src/tools/android/java/com/google/devtools/build/android/desugar/ObjectsRequireNonNullMethodRewriter.java
@@ -25,12 +25,11 @@ import org.objectweb.asm.MethodVisitor;
 /**
  * This class desugars any call to Objects.requireNonNull(Object o), Objects.requireNonNull(Object
  * o, String msg), and Objects.requireNonNull(Object o, Supplier msg), by replacing the call with
- * o.getClass(). Note that currently we discard the message, as inlining the message involves
- * changes to the control flow graph, which further requires re-computation of the stack map frames.
+ * o.getClass().
  */
-public class ObjectsRequireNonNullMethodInliner extends ClassVisitor {
+public class ObjectsRequireNonNullMethodRewriter extends ClassVisitor {
 
-  public ObjectsRequireNonNullMethodInliner(ClassVisitor cv) {
+  public ObjectsRequireNonNullMethodRewriter(ClassVisitor cv) {
     super(ASM5, cv);
   }