Simplify tail-call optimisation check

Check, that all suspension points are immediately followed by ARETURN
and do not check that all these ARETURNs are immediately preceded by
suspension points.
 #KT-27190 Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/coroutines/CoroutineTransformerMethodVisitor.kt

@@ -944,13 +944,7 @@ private fun allSuspensionPointsAreTailCalls(
         }
         if (insideTryBlock) return@all false
 
-        safelyReachableReturns[endIndex + 1]?.all { returnIndex ->
-            sourceFrames[returnIndex].top().sure {
-                "There must be some value on stack to return"
-            }.insns.all { sourceInsn ->
-                sourceInsn?.let(instructions::indexOf) in beginIndex..endIndex
-            }
-        } ?: false
+        safelyReachableReturns[endIndex + 1] != null
     }
 }
 

compiler/testData/codegen/bytecodeListing/tailcall/tailCallIfReturnUnit.kt

@@ -0,0 +1,16 @@
+// WITH_RUNTIME
+
+import kotlin.coroutines.intrinsics.*
+
+fun check() = true
+
+suspend fun f(i: Int): Unit {
+    return f_2()
+}
+
+private inline suspend fun f_2(): Unit {
+    if (check()) return
+    return suspendCoroutineUninterceptedOrReturn {
+        COROUTINE_SUSPENDED
+    }
+}

compiler/testData/codegen/bytecodeListing/tailcall/tailCallIfReturnUnit.txt

@@ -0,0 +1,6 @@
+@kotlin.Metadata
+public final class TailCallIfReturnUnitKt {
+    public final static method check(): boolean
+    public final static @org.jetbrains.annotations.Nullable method f(p0: int, @org.jetbrains.annotations.NotNull p1: kotlin.coroutines.Continuation): java.lang.Object
+    private synthetic final static method f_2(p0: kotlin.coroutines.Continuation): java.lang.Object
+}

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

@@ -493,6 +493,11 @@ public class BytecodeListingTestGenerated extends AbstractBytecodeListingTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeListing/tailcall"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
         }
 
+        @TestMetadata("tailCallIfReturnUnit.kt")
+        public void testTailCallIfReturnUnit() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeListing/tailcall/tailCallIfReturnUnit.kt");
+        }
+
         @TestMetadata("tailCallIntrinsics.kt")
         public void testTailCallIntrinsics_1_2() throws Exception {
             runTestWithPackageReplacement("compiler/testData/codegen/bytecodeListing/tailcall/tailCallIntrinsics.kt", "kotlin.coroutines.experimental");