Index: lib/Sema/SemaStmt.cpp
===================================================================
--- lib/Sema/SemaStmt.cpp
+++ lib/Sema/SemaStmt.cpp
@@ -483,13 +483,6 @@
 Sema::ActOnIfStmt(SourceLocation IfLoc, FullExprArg CondVal, Decl *CondVar,
                   Stmt *thenStmt, SourceLocation ElseLoc,
                   Stmt *elseStmt) {
-  // If the condition was invalid, discard the if statement.  We could recover
-  // better by replacing it with a valid expr, but don't do that yet.
-  if (!CondVal.get() && !CondVar) {
-    getCurFunction()->setHasDroppedStmt();
-    return StmtError();
-  }
-
   ExprResult CondResult(CondVal.release());
 
   VarDecl *ConditionVar = nullptr;
@@ -497,22 +490,22 @@
     ConditionVar = cast<VarDecl>(CondVar);
     CondResult = CheckConditionVariable(ConditionVar, IfLoc, true);
     CondResult = ActOnFinishFullExpr(CondResult.get(), IfLoc);
-    if (CondResult.isInvalid())
-      return StmtError();
   }
   Expr *ConditionExpr = CondResult.getAs<Expr>();
-  if (!ConditionExpr)
-    return StmtError();
+  if (ConditionExpr) {
+    DiagnoseUnusedExprResult(thenStmt);
 
-  DiagnoseUnusedExprResult(thenStmt);
+    if (!elseStmt) {
+      DiagnoseEmptyStmtBody(ConditionExpr->getLocEnd(), thenStmt,
+                            diag::warn_empty_if_body);
+    }
 
-  if (!elseStmt) {
-    DiagnoseEmptyStmtBody(ConditionExpr->getLocEnd(), thenStmt,
-                          diag::warn_empty_if_body);
+    DiagnoseUnusedExprResult(elseStmt);
+  } else {
+    ConditionExpr = new (Context) OpaqueValueExpr(SourceLocation(),
+                                                  Context.VoidTy, VK_RValue);
   }
 
-  DiagnoseUnusedExprResult(elseStmt);
-
   return new (Context) IfStmt(Context, IfLoc, ConditionVar, ConditionExpr,
                               thenStmt, ElseLoc, elseStmt);
 }
Index: test/Misc/ast-dump-invalid.cpp
===================================================================
--- test/Misc/ast-dump-invalid.cpp
+++ test/Misc/ast-dump-invalid.cpp
@@ -18,3 +18,26 @@
 // CHECK-NEXT:         `-CXXUnresolvedConstructExpr {{.*}} <col:10, col:16> 'T'
 // CHECK-NEXT:           |-DeclRefExpr {{.*}} <col:13> 'T' lvalue ParmVar {{.*}} 'i' 'T'
 // CHECK-NEXT:           `-DeclRefExpr {{.*}} <col:16> 'T' lvalue ParmVar {{.*}} 'j' 'T'
+
+
+namespace TestInvalidIf {
+int g(int i) {
+  if (invalid_condition)
+    return 4;
+  else
+    return i;
+}
+}
+// CHECK: NamespaceDecl {{.*}} <{{.*}}> {{.*}} TestInvalidIf
+// CHECK-NEXT: `-FunctionDecl
+// CHECK-NEXT:   |-ParmVarDecl
+// CHECK-NEXT:   `-CompoundStmt
+// CHECK-NEXT:     `-IfStmt {{.*}} <line:25:3, line:28:12>
+// CHECK-NEXT:       |-<<<NULL>>>
+// CHECK-NEXT:       |-OpaqueValueExpr {{.*}} <<invalid sloc>> 'void'
+// CHECK-NEXT:       |-ReturnStmt {{.*}} <line:26:5, col:12>
+// CHECK-NEXT:       | `-IntegerLiteral {{.*}} <col:12> 'int' 4
+// CHECK-NEXT:       `-ReturnStmt {{.*}} <line:28:5, col:12>
+// CHECK-NEXT:         `-ImplicitCastExpr {{.*}} <col:12> 'int' <LValueToRValue>
+// CHECK-NEXT:           `-DeclRefExpr {{.*}} <col:12> 'int' lvalue ParmVar {{.*}} 'i' 'int'
+