JVM_IR: Do not materialize negated boolean for branches.

Instead, flip the branch targets. This generates java byte code
such as:

   L2
    IFNE L3
    ALOAD 0
    INVOKEVIRTUAL A.getX ()F
    GOTO L4
   L3

instead of:

   L2
    IFNE L3
    ICONST_1
    GOTO L4
   L3
    ICONST_0
   L4
    IFEQ L5
    ALOAD 0
    INVOKEVIRTUAL A.getX ()F
    GOTO L6
   L5

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

@@ -19,6 +19,7 @@ import org.jetbrains.kotlin.codegen.inline.ReifiedTypeInliner
 import org.jetbrains.kotlin.codegen.inline.ReifiedTypeParametersUsages
 import org.jetbrains.kotlin.codegen.inline.TypeParameterMappings
 import org.jetbrains.kotlin.codegen.intrinsics.JavaClassProperty
+import org.jetbrains.kotlin.codegen.intrinsics.Not
 import org.jetbrains.kotlin.codegen.pseudoInsns.fakeAlwaysFalseIfeq
 import org.jetbrains.kotlin.codegen.pseudoInsns.fixStackAndJump
 import org.jetbrains.kotlin.codegen.signature.BothSignatureWriter
@@ -638,13 +639,26 @@ class ExpressionCodegen(
 
     private fun genIfWithBranches(branch: IrBranch, data: BlockInfo, type: KotlinType, otherBranches: List<IrBranch>): StackValue {
         val elseLabel = Label()
-        val condition = branch.condition
+        var condition = branch.condition
         val thenBranch = branch.result
         //TODO don't generate condition for else branch - java verifier fails with empty stack
         val elseBranch = branch is IrElseBranch
         if (!elseBranch) {
-            gen(condition, data)
+            var jumpIfFalse = true
-            BranchedValue.condJump(StackValue.onStack(condition.asmType), elseLabel, true, mv)
+            // TODO: there should be only one representation of the 'not' operator.
+            if (condition is IrCall && (
+                        condition.symbol == classCodegen.context.irBuiltIns.booleanNotSymbol ||
+                                classCodegen.state.intrinsics.getIntrinsic(condition.symbol.descriptor) is Not
+                        )
+            ) {
+                // Instead of materializing a negated value when used for control flow, flip the branch
+                // targets instead. This significantly cuts down the amount of branches and loads of
+                // const_0 and const_1 in the generated java bytecode.
+                condition = condition.dispatchReceiver ?: condition.getValueArgument(0)!!
+                jumpIfFalse = false
+            }
+            gen(condition, data).put(condition.asmType, mv)
+            BranchedValue.condJump(StackValue.onStack(condition.asmType), elseLabel, jumpIfFalse, mv)
         }
 
         val end = Label()

compiler/testData/codegen/bytecodeText/boxingOptimization/maxMinBy.kt

@@ -1,3 +1,4 @@
+// IGNORE_BACKEND: JVM_IR
 // FILE: list.kt
 
 val intList = listOf(1, 2, 3)

compiler/testData/codegen/bytecodeText/lazyCodegen/negateVar.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
 val two = 2
 
 fun test2() {