JVM_IR: defer some branch optimizations to codegen.

Specifically, defer the removal of hand-written "if (true|false)" from
JvmBuiltinOptimizationLowering into codegen so that appropriate debug
info (and a NOP) can be inserted.

Change-Id: Ia11af05ad8b4251946bd3e685fb7c3319f0f433f

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -39,9 +39,7 @@ import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.isMarkedNullable
 import org.jetbrains.kotlin.ir.types.isNothing
 import org.jetbrains.kotlin.ir.types.toKotlinType
-import org.jetbrains.kotlin.ir.util.dump
+import org.jetbrains.kotlin.ir.util.*
-import org.jetbrains.kotlin.ir.util.isNullConst
-import org.jetbrains.kotlin.ir.util.render
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.DescriptorUtils.isEnumClass
@@ -694,31 +692,52 @@ class ExpressionCodegen(
     }
 
     private fun genIfWithBranches(branch: IrBranch, data: BlockInfo, type: KotlinType, otherBranches: List<IrBranch>): StackValue {
+        // True or false conditions known at compile time need not be generated.
+        val shouldGenerateCondition = !branch.condition.isFalseConst() && !branch.condition.isTrueConst()
+        // Body of an always-false-condition need not be generated.
+        val shouldGenerateBody = !branch.condition.isFalseConst()
+        // Don't generate the tail if it doesn't exist or isn't reachable.
+        val shouldGenerateTail = !otherBranches.isEmpty() && !branch.condition.isTrueConst()
+
         val elseLabel = Label()
-        val thenBranch = branch.result
+        val endLabel = Label()
-        //TODO don't generate condition for else branch - java verifier fails with empty stack
+
-        val elseBranch = branch is IrElseBranch
+        if (shouldGenerateCondition) {
-        if (!elseBranch) {
             genConditionWithOptimizationsIfPossible(branch, data, elseLabel)
+        } else {
+            // Even when a condition isn't generated, a linenumber and nop is still required so that a debugger can break on the line of the
+            // condition, except for the explicit "else".
+            if (branch !is IrElseBranch) {
+                branch.condition.markLineNumber(startOffset = true)
+                mv.nop()
+            }
         }
 
-        val end = Label()
+        val resultFromBody = if (shouldGenerateBody) {
-
+            val thenBranch = branch.result
-        val result = thenBranch.run {
+            val result = thenBranch.run {
-            val stackValue = gen(this, data)
+                val stackValue = gen(this, data)
-            coerceNotToUnit(stackValue.type, stackValue.kotlinType, type)
+                coerceNotToUnit(stackValue.type, stackValue.kotlinType, type)
+            }
+            mv.goTo(endLabel)
+            mv.mark(elseLabel)
+            result
+        } else {
+            none()
         }
 
-        mv.goTo(end)
+        val resultFromTail = if (shouldGenerateTail) {
-        mv.mark(elseLabel)
-
-        if (!otherBranches.isEmpty()) {
             val nextBranch = otherBranches.first()
             genIfWithBranches(nextBranch, data, type, otherBranches.drop(1))
+        } else {
+            none()
         }
 
-        mv.mark(end)
+        // endLabel is only used to jump from end-of-then-body to the end of the whole if cascade.
-        return result
+        if (shouldGenerateBody)
+            mv.mark(endLabel)
+
+        return if (shouldGenerateBody) resultFromBody else resultFromTail
     }
 
     private fun genConditionWithOptimizationsIfPossible(branch: IrBranch, data: BlockInfo, elseLabel: Label) {

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/JvmBuiltinOptimizationLowering.kt

@@ -109,10 +109,11 @@ class JvmBuiltinOptimizationLowering(val context: JvmBackendContext) : FileLower
             }
 
             override fun visitWhen(expression: IrWhen): IrExpression {
+                val isCompilerGenerated = expression.origin == null
                 expression.transformChildrenVoid(this)
                 // Remove all branches with constant false condition.
                 expression.branches.removeIf() {
-                    it.condition.isFalseConst()
+                    it.condition.isFalseConst() && isCompilerGenerated
                 }
                 // If the only condition that is left has a constant true condition remove the
                 // when in favor of the result. If there are no conditions left, remove the when
@@ -120,7 +121,7 @@ class JvmBuiltinOptimizationLowering(val context: JvmBackendContext) : FileLower
                 return if (expression.branches.size == 0) {
                     IrBlockImpl(expression.startOffset, expression.endOffset, context.irBuiltIns.unitType)
                 } else {
-                    expression.branches.first().takeIf { it.condition.isTrueConst() }?.result ?: expression
+                    expression.branches.first().takeIf { it.condition.isTrueConst() && isCompilerGenerated }?.result ?: expression
                 }
             }
 

compiler/testData/codegen/box/controlStructures/ifConst1.kt

@@ -0,0 +1,19 @@
+fun foo(b: Boolean): String {
+    return if (b) {
+        "OK"
+    } else if (false) {
+        "fail: reached unreachable code at line 5"
+    } else if (true) {
+        "fail: reached unexpected code at line 7"
+    } else if (true) {
+        "fail: reached unreachable code at line 9"
+    } else if (b) {
+        "fail: reached unreachable code at line 11"
+    } else {
+        "fail: reached unreachable code at line 13"
+    }
+}
+
+fun box(): String {
+    return foo(true)
+}

compiler/testData/codegen/box/controlStructures/ifConst2.kt

@@ -0,0 +1,19 @@
+fun foo(b: Boolean): String {
+    return if (b) {
+        "fail: reached unexpected code at line 3"
+    } else if (false) {
+        "fail: reached unreachable code at line 5"
+    } else if (true) {
+        "OK"
+    } else if (true) {
+        "fail: reached unreachable code at line 9"
+    } else if (b) {
+        "fail: reached unreachable code at line 11"
+    } else {
+        "fail: reached unreachable code at line 13"
+    }
+}
+
+fun box(): String {
+    return foo(false)
+}

compiler/testData/codegen/bytecodeText/controlStructures/ifConsts.kt

@@ -0,0 +1,19 @@
+fun foo(b: Boolean): Int {
+    return if (b) {
+        100
+    } else if (false) {
+        101
+    } else if (true) {
+        102
+    } else if (true) {
+        103
+    } else if (b) {
+        104
+    } else {
+        105
+    }
+}
+
+// 2 BIPUSH
+// 1 BIPUSH 100
+// 1 BIPUSH 102

compiler/testData/codegen/bytecodeText/lineNumbers/ifConsts.kt

@@ -0,0 +1,35 @@
+fun cond() = false
+
+fun bar() {}
+
+fun foo() {
+    if (cond()) {
+        bar()
+    } else if (true) {
+        bar()
+    } else {
+        bar()
+    }
+
+    if (false) {
+        bar()
+    } else if (true) {
+        bar()
+    } else {
+        bar()
+    }
+
+    if (true) {
+        bar()
+    } else if (false) {
+        bar()
+    } else {
+        bar()
+    }
+}
+
+// 1 LINENUMBER 6
+// 1 LINENUMBER 8
+// 1 LINENUMBER 14
+// 1 LINENUMBER 16
+// 1 LINENUMBER 22

compiler/testData/codegen/bytecodeText/lineNumbers/ifFalse.kt

@@ -0,0 +1,7 @@
+fun foo(): Int {
+    if (false) {
+        return 1
+    }
+    return 2
+}
+// 1 LINENUMBER 2

compiler/testData/codegen/bytecodeText/lineNumbers/ifFalseElse.kt

@@ -0,0 +1,8 @@
+fun foo(): Int {
+    if (false) {
+        return 1
+    } else {
+        return 2
+    }
+}
+// 1 LINENUMBER 2

compiler/testData/codegen/bytecodeText/lineNumbers/ifTrue.kt

@@ -0,0 +1,7 @@
+fun foo(): Int {
+    if (true) {
+        return 1
+    }
+    return 2
+}
+// 1 LINENUMBER 2

compiler/testData/codegen/bytecodeText/lineNumbers/ifTrueElse.kt

@@ -0,0 +1,8 @@
+fun foo(): Int {
+    if (true) {
+        return 1
+    } else {
+        return 2
+    }
+}
+// 1 LINENUMBER 2

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -4673,6 +4673,16 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/controlStructures/forUserType.kt");
         }
 
+        @TestMetadata("ifConst1.kt")
+        public void testIfConst1() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst1.kt");
+        }
+
+        @TestMetadata("ifConst2.kt")
+        public void testIfConst2() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -1106,6 +1106,11 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeText/controlStructures"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("ifConsts.kt")
+        public void testIfConsts() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/controlStructures/ifConsts.kt");
+        }
+
         @TestMetadata("kt17110.kt")
         public void testKt17110() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/controlStructures/kt17110.kt");
@@ -2640,11 +2645,36 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeText/lineNumbers"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("ifConsts.kt")
+        public void testIfConsts() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifConsts.kt");
+        }
+
         @TestMetadata("ifElse.kt")
         public void testIfElse() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifElse.kt");
         }
 
+        @TestMetadata("ifFalse.kt")
+        public void testIfFalse() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifFalse.kt");
+        }
+
+        @TestMetadata("ifFalseElse.kt")
+        public void testIfFalseElse() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifFalseElse.kt");
+        }
+
+        @TestMetadata("ifTrue.kt")
+        public void testIfTrue() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifTrue.kt");
+        }
+
+        @TestMetadata("ifTrueElse.kt")
+        public void testIfTrueElse() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifTrueElse.kt");
+        }
+
         @TestMetadata("singleThen.kt")
         public void testSingleThen() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/lineNumbers/singleThen.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -4673,6 +4673,16 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/controlStructures/forUserType.kt");
         }
 
+        @TestMetadata("ifConst1.kt")
+        public void testIfConst1() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst1.kt");
+        }
+
+        @TestMetadata("ifConst2.kt")
+        public void testIfConst2() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -4673,6 +4673,16 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/controlStructures/forUserType.kt");
         }
 
+        @TestMetadata("ifConst1.kt")
+        public void testIfConst1() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst1.kt");
+        }
+
+        @TestMetadata("ifConst2.kt")
+        public void testIfConst2() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBytecodeTextTestGenerated.java

@@ -1106,6 +1106,11 @@ public class IrBytecodeTextTestGenerated extends AbstractIrBytecodeTextTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeText/controlStructures"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM_IR, true);
         }
 
+        @TestMetadata("ifConsts.kt")
+        public void testIfConsts() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/controlStructures/ifConsts.kt");
+        }
+
         @TestMetadata("kt17110.kt")
         public void testKt17110() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/controlStructures/kt17110.kt");
@@ -2640,11 +2645,36 @@ public class IrBytecodeTextTestGenerated extends AbstractIrBytecodeTextTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeText/lineNumbers"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM_IR, true);
         }
 
+        @TestMetadata("ifConsts.kt")
+        public void testIfConsts() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifConsts.kt");
+        }
+
         @TestMetadata("ifElse.kt")
         public void testIfElse() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifElse.kt");
         }
 
+        @TestMetadata("ifFalse.kt")
+        public void testIfFalse() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifFalse.kt");
+        }
+
+        @TestMetadata("ifFalseElse.kt")
+        public void testIfFalseElse() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifFalseElse.kt");
+        }
+
+        @TestMetadata("ifTrue.kt")
+        public void testIfTrue() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifTrue.kt");
+        }
+
+        @TestMetadata("ifTrueElse.kt")
+        public void testIfTrueElse() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/lineNumbers/ifTrueElse.kt");
+        }
+
         @TestMetadata("singleThen.kt")
         public void testSingleThen() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/lineNumbers/singleThen.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/IrJsCodegenBoxTestGenerated.java

@@ -3858,6 +3858,16 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/controlStructures/forUserType.kt");
         }
 
+        @TestMetadata("ifConst1.kt")
+        public void testIfConst1() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst1.kt");
+        }
+
+        @TestMetadata("ifConst2.kt")
+        public void testIfConst2() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -3868,6 +3868,16 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             runTest("compiler/testData/codegen/box/controlStructures/forUserType.kt");
         }
 
+        @TestMetadata("ifConst1.kt")
+        public void testIfConst1() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst1.kt");
+        }
+
+        @TestMetadata("ifConst2.kt")
+        public void testIfConst2() throws Exception {
+            runTest("compiler/testData/codegen/box/controlStructures/ifConst2.kt");
+        }
+
         @TestMetadata("inRangeConditionsInWhen.kt")
         public void testInRangeConditionsInWhen() throws Exception {
             runTest("compiler/testData/codegen/box/controlStructures/inRangeConditionsInWhen.kt");