[DI] InitAccessors: Ignore unreachable blocks when check property initialization inside of an init accessor

Author: xedin

Diff for: lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -1182,6 +1182,12 @@ void LifetimeChecker::doIt() {
     while (returnBB != F.end()) {
       auto *terminator = returnBB->getTerminator();
 
+      // If this is an unreachable block, let's ignore it.
+      if (isa<UnreachableInst>(terminator)) {
+        ++returnBB;
+        continue;
+      }
+
       if (!isInitializedAtUse(DIMemoryUse(terminator, DIUseKind::Load, 0, 1)))
         diagnoseMissingInit();
 

Diff for: test/SILOptimizer/init_accessor_definite_init_diagnostics.swift

@@ -189,6 +189,17 @@ class TestInitWithGuard {
   }
 }
 
+do {
+  struct TestPropertyInitWithUnreachableBlocks {
+    var _a: Int
+    var a: Int? {
+      @storageRestrictions(initializes: _a)
+      init { _a = newValue ?? 0 } // Ok
+      get { 42 }
+    }
+  }
+}
+
 do {
   class Base<T: Collection> {
     private var _v: T