Merge pull request #4963 from lrytz/simplerBranching

Generate leaner code for branches

3 files changed, 127 insertions, 5 deletions

diff --git a/test/junit/scala/issues/BytecodeTest.scala b/test/junit/scala/issues/BytecodeTest.scala
index 7260f43c87..ca1b33ed20 100644
--- a/test/junit/scala/issues/BytecodeTest.scala
+++ b/test/junit/scala/issues/BytecodeTest.scala
@@ -3,7 +3,7 @@ package scala.issues
 import org.junit.runner.RunWith
 import org.junit.runners.JUnit4
 import org.junit.Test
-import scala.tools.asm.Opcodes
+import scala.tools.asm.Opcodes._
 import scala.tools.nsc.backend.jvm.AsmUtils
 import scala.tools.nsc.backend.jvm.CodeGenTools._
 import org.junit.Assert._
@@ -105,12 +105,10 @@ class BytecodeTest extends ClearAfterClass {
     val unapplyLineNumbers = getSingleMethod(module, "unapply").instructions.filter(_.isInstanceOf[LineNumber])
     assert(unapplyLineNumbers == List(LineNumber(2, Label(0))), unapplyLineNumbers)
 
-    import Opcodes._
     val expected = List(
       LineNumber(4, Label(0)),
       LineNumber(5, Label(5)),
-      Jump(IFNE, Label(11)),
-      Jump(GOTO, Label(20)),
+      Jump(IFEQ, Label(20)),
 
       LineNumber(6, Label(11)),
       Invoke(INVOKEVIRTUAL, "scala/Predef$", "println", "(Ljava/lang/Object;)V", false),
@@ -133,4 +131,81 @@ class BytecodeTest extends ClearAfterClass {
     }
     assertSameCode(mainIns, expected)
   }
+
+  @Test
+  def bytecodeForBranches(): Unit = {
+    val code =
+      """class C {
+        |  def t1(b: Boolean) = if (b) 1 else 2
+        |  def t2(x: Int) = if (x == 393) 1 else 2
+        |  def t3(a: Array[String], b: AnyRef) = a != b && b == a
+        |  def t4(a: AnyRef) = a == null || null != a
+        |  def t5(a: AnyRef) = (a eq null) || (null ne a)
+        |  def t6(a: Int, b: Boolean) = if ((a == 10) && b || a != 1) 1 else 2
+        |  def t7(a: AnyRef, b: AnyRef) = a == b
+        |  def t8(a: AnyRef) = Nil == a || "" != a
+        |}
+      """.stripMargin
+
+    val List(c) = compileClasses(compiler)(code)
+
+    // t1: no unnecessary GOTOs
+    assertSameCode(getSingleMethod(c, "t1").instructions.dropNonOp, List(
+      VarOp(ILOAD, 1), Jump(IFEQ, Label(6)),
+      Op(ICONST_1), Jump(GOTO, Label(9)),
+      Label(6), Op(ICONST_2),
+      Label(9), Op(IRETURN)))
+
+    // t2: no unnecessary GOTOs
+    assertSameCode(getSingleMethod(c, "t2").instructions.dropNonOp, List(
+      VarOp(ILOAD, 1), IntOp(SIPUSH, 393), Jump(IF_ICMPNE, Label(7)),
+      Op(ICONST_1), Jump(GOTO, Label(10)),
+      Label(7), Op(ICONST_2),
+      Label(10), Op(IRETURN)))
+
+    // t3: Array == is translated to reference equality, AnyRef == to null checks and equals
+    assertSameCode(getSingleMethod(c, "t3").instructions.dropNonOp, List(
+      // Array ==
+      VarOp(ALOAD, 1), VarOp(ALOAD, 2), Jump(IF_ACMPEQ, Label(23)),
+      // AnyRef ==
+      VarOp(ALOAD, 2), VarOp(ALOAD, 1), VarOp(ASTORE, 3), Op(DUP), Jump(IFNONNULL, Label(14)),
+      Op(POP), VarOp(ALOAD, 3), Jump(IFNULL, Label(19)), Jump(GOTO, Label(23)),
+      Label(14), VarOp(ALOAD, 3), Invoke(INVOKEVIRTUAL, "java/lang/Object", "equals", "(Ljava/lang/Object;)Z", false), Jump(IFEQ, Label(23)),
+      Label(19), Op(ICONST_1), Jump(GOTO, Label(26)),
+      Label(23), Op(ICONST_0),
+      Label(26), Op(IRETURN)))
+
+    val t4t5 = List(
+      VarOp(ALOAD, 1), Jump(IFNULL, Label(6)),
+      VarOp(ALOAD, 1), Jump(IFNULL, Label(10)),
+      Label(6), Op(ICONST_1), Jump(GOTO, Label(13)),
+      Label(10), Op(ICONST_0),
+      Label(13), Op(IRETURN))
+
+    // t4: one side is known null, so just a null check on the other
+    assertSameCode(getSingleMethod(c, "t4").instructions.dropNonOp, t4t5)
+
+    // t5: one side known null, so just a null check on the other
+    assertSameCode(getSingleMethod(c, "t5").instructions.dropNonOp, t4t5)
+
+    // t6: no unnecessary GOTOs
+    assertSameCode(getSingleMethod(c, "t6").instructions.dropNonOp, List(
+      VarOp(ILOAD, 1), IntOp(BIPUSH, 10), Jump(IF_ICMPNE, Label(7)),
+      VarOp(ILOAD, 2), Jump(IFNE, Label(12)),
+      Label(7), VarOp(ILOAD, 1), Op(ICONST_1), Jump(IF_ICMPEQ, Label(16)),
+      Label(12), Op(ICONST_1), Jump(GOTO, Label(19)),
+      Label(16), Op(ICONST_2),
+      Label(19), Op(IRETURN)))
+
+    // t7: universal equality
+    assertInvoke(getSingleMethod(c, "t7"), "scala/runtime/BoxesRunTime", "equals")
+
+    // t8: no null checks invoking equals on modules and constants
+    assertSameCode(getSingleMethod(c, "t8").instructions.dropNonOp, List(
+      Field(GETSTATIC, "scala/collection/immutable/Nil$", "MODULE$", "Lscala/collection/immutable/Nil$;"), VarOp(ALOAD, 1), Invoke(INVOKEVIRTUAL, "java/lang/Object", "equals", "(Ljava/lang/Object;)Z", false), Jump(IFNE, Label(10)),
+      Ldc(LDC, ""), VarOp(ALOAD, 1), Invoke(INVOKEVIRTUAL, "java/lang/Object", "equals", "(Ljava/lang/Object;)Z", false), Jump(IFNE, Label(14)),
+      Label(10), Op(ICONST_1), Jump(GOTO, Label(17)),
+      Label(14), Op(ICONST_0),
+      Label(17), Op(IRETURN)))
+  }
 }
diff --git a/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala b/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala
index 942b62b32c..70f3060027 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala
@@ -1507,7 +1507,6 @@ class InlinerTest extends ClearAfterClass {
         |}
       """.stripMargin
     val List(c) = compile(code)
-    val t = getSingleMethod(c, "t")
 
     // box-unbox will clean it up
     assertEquals(getSingleMethod(c, "t").instructions.summary,
diff --git a/test/junit/scala/tools/nsc/backend/jvm/opt/UnreachableCodeTest.scala b/test/junit/scala/tools/nsc/backend/jvm/opt/UnreachableCodeTest.scala
index 86c8baa3c6..62ee09e9de 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/opt/UnreachableCodeTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/opt/UnreachableCodeTest.scala
@@ -215,4 +215,52 @@ class UnreachableCodeTest extends ClearAfterClass {
     assertTrue(List(FrameEntry(F_FULL, List(INTEGER, DOUBLE, Label(3)), List("java/lang/Object", Label(4))), Label(3), Label(4)) ===
                List(FrameEntry(F_FULL, List(INTEGER, DOUBLE, Label(1)), List("java/lang/Object", Label(3))), Label(1), Label(3)))
   }
+
+  @Test
+  def loadNullNothingBytecode(): Unit = {
+    val code =
+      """class C {
+        |  def nl: Null = null
+        |  def nt: Nothing = throw new Error("")
+        |  def cons(a: Any) = ()
+        |
+        |  def t1 = cons(null)
+        |  def t2 = cons(nl)
+        |  def t3 = cons(throw new Error(""))
+        |  def t4 = cons(nt)
+        |}
+      """.stripMargin
+    val List(c) = compileClasses(noOptCompiler)(code)
+
+    assertEquals(getSingleMethod(c, "nl").instructions.summary, List(ACONST_NULL, ARETURN))
+
+    assertEquals(getSingleMethod(c, "nt").instructions.summary, List(
+      NEW, DUP, LDC, "<init>", ATHROW))
+
+    assertEquals(getSingleMethod(c, "t1").instructions.summary, List(
+      ALOAD, ACONST_NULL, "cons", RETURN))
+
+    // GenBCode introduces POP; ACONST_NULL after loading an expression of type scala.runtime.Null$,
+    // see comment in BCodeBodyBuilder.adapt
+    assertEquals(getSingleMethod(c, "t2").instructions.summary, List(
+      ALOAD, ALOAD, "nl", POP, ACONST_NULL, "cons", RETURN))
+
+    // the bytecode generated by GenBCode is ... ATHROW; INVOKEVIRTUAL C.cons; RETURN
+    // the ASM classfile writer creates a new basic block (creates a label) right after the ATHROW
+    // and replaces all instructions by NOP*; ATHROW, see comment in BCodeBodyBuilder.adapt
+    // NOTE: DCE is enabled by default and gets rid of the redundant code (tested below)
+    assertEquals(getSingleMethod(c, "t3").instructions.summary, List(
+      ALOAD, NEW, DUP, LDC, "<init>", ATHROW, NOP, NOP, NOP, ATHROW))
+
+    // GenBCode introduces an ATHROW after the invocation of C.nt, see BCodeBodyBuilder.adapt
+    // NOTE: DCE is enabled by default and gets rid of the redundant code (tested below)
+    assertEquals(getSingleMethod(c, "t4").instructions.summary, List(
+      ALOAD, ALOAD, "nt", ATHROW, NOP, NOP, NOP, ATHROW))
+
+    val List(cDCE) = compileClasses(dceCompiler)(code)
+    assertEquals(getSingleMethod(cDCE, "t3").instructions.summary, List(
+      ALOAD, NEW, DUP, LDC, "<init>", ATHROW))
+    assertEquals(getSingleMethod(cDCE, "t4").instructions.summary, List(
+      ALOAD, ALOAD, "nt", ATHROW))
+  }
 }