Index: clang/include/clang/Lex/Preprocessor.h
===================================================================
--- clang/include/clang/Lex/Preprocessor.h
+++ clang/include/clang/Lex/Preprocessor.h
@@ -325,6 +325,10 @@
   /// This is used when loading a precompiled preamble.
   std::pair<int, bool> SkipMainFilePreamble;
 
+  /// Whether we hit an error due to reaching max allowed include depth. Allows
+  /// to avoid hitting the same error over and over again.
+  bool HasReachedMaxIncludeDepth = false;
+
 public:
   struct PreambleSkipInfo {
     SourceLocation HashTokenLoc;
Index: clang/lib/Lex/PPDirectives.cpp
===================================================================
--- clang/lib/Lex/PPDirectives.cpp
+++ clang/lib/Lex/PPDirectives.cpp
@@ -35,6 +35,7 @@
 #include "clang/Lex/Token.h"
 #include "clang/Lex/VariadicMacroSupport.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/STLExtras.h"
@@ -1794,6 +1795,7 @@
   // Check that we don't have infinite #include recursion.
   if (IncludeMacroStack.size() == MaxAllowedIncludeStackDepth-1) {
     Diag(FilenameTok, diag::err_pp_include_too_deep);
+    HasReachedMaxIncludeDepth = true;
     return;
   }
 
@@ -1942,10 +1944,11 @@
   if (PPOpts->SingleFileParseMode)
     ShouldEnter = false;
 
-  // Any diagnostics after the fatal error will not be visible. As the
-  // compilation failed already and errors in subsequently included files won't
-  // be visible, avoid preprocessing those files.
-  if (ShouldEnter && Diags->hasFatalErrorOccurred())
+  // If we've reached the max allowed include depth, it is usually due to an
+  // include cycle. Don't enter already processed files again as it can lead to
+  // reaching the max allowed include depth again.
+  if (ShouldEnter && HasReachedMaxIncludeDepth && File &&
+      HeaderInfo.getFileInfo(File).NumIncludes)
     ShouldEnter = false;
 
   // Determine whether we should try to import the module for this #include, if
Index: clang/test/Index/Inputs/cycle.h
===================================================================
--- /dev/null
+++ clang/test/Index/Inputs/cycle.h
@@ -0,0 +1 @@
+#include "cycle.h"
Index: clang/test/Index/keep-going-include-cycle.c
===================================================================
--- /dev/null
+++ clang/test/Index/keep-going-include-cycle.c
@@ -0,0 +1,10 @@
+#include "cycle.h"
+#include "foo.h"
+
+// RUN: env CINDEXTEST_KEEP_GOING=1 c-index-test -test-print-type -I%S/Inputs %s 2> %t.stderr.txt | FileCheck %s
+// RUN: FileCheck -check-prefix CHECK-DIAG %s < %t.stderr.txt
+
+// Verify that we don't stop preprocessing after an include cycle.
+// CHECK: VarDecl=global_var:1:12 [type=int] [typekind=Int] [isPOD=1]
+
+// CHECK-DIAG: cycle.h:1:10: error: #include nested too deeply
Index: clang/test/Index/keep-going.cpp
===================================================================
--- clang/test/Index/keep-going.cpp
+++ clang/test/Index/keep-going.cpp
@@ -9,11 +9,18 @@
 
 class C : public A<float> { };
 
-// RUN: env CINDEXTEST_EDITING=1 CINDEXTEST_KEEP_GOING=1 c-index-test -test-print-type %s -std=c++03 2> %t.stderr.txt  | FileCheck %s
+// Not found includes shouldn't affect subsequent correct includes.
+#include "foo.h"
+
+// RUN: env CINDEXTEST_EDITING=1 CINDEXTEST_KEEP_GOING=1 c-index-test -test-print-type -I%S/Inputs %s -std=c++03 2> %t.stderr.txt  | FileCheck %s
 // RUN: FileCheck -check-prefix CHECK-DIAG %s < %t.stderr.txt
 
+// Verify that even without CINDEXTEST_EDITING we don't stop processing after a fatal error.
+// RUN: env CINDEXTEST_KEEP_GOING=1 c-index-test -test-print-type -I%S/Inputs %s -std=c++03 2> %t.stderr.txt  | FileCheck -check-prefix CHECK-KEEP-GOING-ONLY %s
+
 // CHECK: inclusion directive=missing1.h ((null)) [type=] [typekind=Invalid] [isPOD=0]
 // CHECK: inclusion directive=missing2.h ((null)) [type=] [typekind=Invalid] [isPOD=0]
+// CHECK: inclusion directive=foo.h ({{.*[/\\]}}test{{[/\\]}}Index{{[/\\]}}Inputs{{[/\\]}}foo.h) [type=] [typekind=Invalid] [isPOD=0]
 // CHECK: ClassTemplate=A:4:7 (Definition) [type=] [typekind=Invalid] [isPOD=0]
 // CHECK: TemplateTypeParameter=T:3:16 (Definition) [type=T] [typekind=Unexposed] [canonicaltype=type-parameter-0-0] [canonicaltypekind=Unexposed] [isPOD=0]
 // CHECK: FieldDecl=a:4:13 (Definition) [type=T] [typekind=Unexposed] [canonicaltype=type-parameter-0-0] [canonicaltypekind=Unexposed] [isPOD=0]
@@ -25,5 +32,7 @@
 // CHECK: C++ base class specifier=A<float>:4:7 [access=public isVirtual=false] [type=A<float>] [typekind=Unexposed] [templateargs/1= [type=float] [typekind=Float]] [canonicaltype=A<float>] [canonicaltypekind=Record] [canonicaltemplateargs/1= [type=float] [typekind=Float]] [isPOD=0] [nbFields=1]
 // CHECK: TemplateRef=A:4:7 [type=] [typekind=Invalid] [isPOD=0]
 
+// CHECK-KEEP-GOING-ONLY: VarDecl=global_var:1:12 [type=int] [typekind=Int] [isPOD=1]
+
 // CHECK-DIAG: keep-going.cpp:1:10: fatal error: 'missing1.h' file not found
 // CHECK-DIAG: keep-going.cpp:8:10: fatal error: 'missing2.h' file not found