backend: fix minor bug in evaluateWhen

Also add the corresponding test 'when9'.

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/IrToBitcode.kt

@@ -1151,9 +1151,13 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
         if (!isNothing)                                     // If "when" has "exit".
             bbExit = codegen.basicBlock()                   // Create basic block to process "exit".
 
-        val resultPhi = if (isUnit || isNothing) null else
+        val hasNoValue = !isUnconditional(expression.branches.last())
+        // (It is possible if IrWhen is used as statement).
+
+        val llvmType = codegen.getLLVMType(expression.type)
+        val resultPhi = if (isUnit || isNothing || hasNoValue) null else
             codegen.appendingTo(bbExit!!) {
-                codegen.phi(codegen.getLLVMType(expression.type))
+                codegen.phi(llvmType)
             }
 
         expression.branches.forEach {                           // Iterate through "when" branches (clauses).
@@ -1167,6 +1171,7 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
             // FIXME: remove the hacks.
             isUnit -> codegen.theUnitInstanceRef.llvm
             isNothing -> codegen.kNothingFakeValue
+            hasNoValue -> LLVMGetUndef(llvmType)!!
             else -> resultPhi!!
         }
     }

backend.native/tests/build.gradle

@@ -330,6 +330,11 @@ task when8(type: RunKonanTest) {
     goldValue = "true\n"
 }
 
+task when9(type: RunKonanTest) {
+    goldValue = "Ok\n"
+    source = "codegen/branching/when9.kt"
+}
+
 task when_through(type: RunKonanTest) {
     source = "codegen/branching/when_through.kt"
 }

backend.native/tests/codegen/branching/when9.kt

@@ -0,0 +1,10 @@
+fun main(args: Array<String>) {
+    foo(0)
+    println("Ok")
+}
+
+fun foo(x: Int) {
+    when (x) {
+        0 -> 0
+    }
+}