Index: include/clang/Basic/AllDiagnostics.h
===================================================================
--- include/clang/Basic/AllDiagnostics.h
+++ include/clang/Basic/AllDiagnostics.h
@@ -32,6 +32,29 @@
 public:
   enum { Size = SizeOfStr };
 };
+
+#define STRINGIFY_NAME(NAME) #NAME
+#define VALIDATE_DIAG_SIZE(NAME)                                               \
+  static_assert(                                                               \
+      static_cast<unsigned>(diag::NUM_BUILTIN_##NAME##_DIAGNOSTICS) <          \
+          static_cast<unsigned>(diag::DIAG_START_##NAME) +                     \
+              static_cast<unsigned>(diag::DIAG_SIZE_##NAME),                   \
+      STRINGIFY_NAME(                                                          \
+          DIAG_SIZE_##NAME) " is insufficient to contain all "                 \
+                            "diagnostics, it may need to be made larger in "   \
+                            "DiagnosticIDs.h.");
+VALIDATE_DIAG_SIZE(COMMON)
+VALIDATE_DIAG_SIZE(DRIVER)
+VALIDATE_DIAG_SIZE(FRONTEND)
+VALIDATE_DIAG_SIZE(SERIALIZATION)
+VALIDATE_DIAG_SIZE(LEX)
+VALIDATE_DIAG_SIZE(PARSE)
+VALIDATE_DIAG_SIZE(AST)
+VALIDATE_DIAG_SIZE(COMMENT)
+VALIDATE_DIAG_SIZE(SEMA)
+VALIDATE_DIAG_SIZE(ANALYSIS)
+#undef VALIDATE_DIAG_SIZE
+#undef STRINGIFY_NAME
 } // end namespace clang 
 
 #define STR_SIZE(str, fieldTy) clang::StringSizerHelper<sizeof(str)-1, \
Index: include/clang/Basic/DiagnosticIDs.h
===================================================================
--- include/clang/Basic/DiagnosticIDs.h
+++ include/clang/Basic/DiagnosticIDs.h
@@ -26,19 +26,32 @@
 
   // Import the diagnostic enums themselves.
   namespace diag {
+    // Size of each of the diagnostic categories.
+    enum {
+      DIAG_SIZE_COMMON        =  300,
+      DIAG_SIZE_DRIVER        =  200,
+      DIAG_SIZE_FRONTEND      =  100,
+      DIAG_SIZE_SERIALIZATION =  120,
+      DIAG_SIZE_LEX           =  400,
+      DIAG_SIZE_PARSE         =  500,
+      DIAG_SIZE_AST           =  110,
+      DIAG_SIZE_COMMENT       =  100,
+      DIAG_SIZE_SEMA          = 3500,
+      DIAG_SIZE_ANALYSIS      =  100
+    };
     // Start position for diagnostics.
     enum {
-      DIAG_START_COMMON        =                                 0,
-      DIAG_START_DRIVER        = DIAG_START_COMMON          +  300,
-      DIAG_START_FRONTEND      = DIAG_START_DRIVER          +  200,
-      DIAG_START_SERIALIZATION = DIAG_START_FRONTEND        +  100,
-      DIAG_START_LEX           = DIAG_START_SERIALIZATION   +  120,
-      DIAG_START_PARSE         = DIAG_START_LEX             +  400,
-      DIAG_START_AST           = DIAG_START_PARSE           +  500,
-      DIAG_START_COMMENT       = DIAG_START_AST             +  110,
-      DIAG_START_SEMA          = DIAG_START_COMMENT         +  100,
-      DIAG_START_ANALYSIS      = DIAG_START_SEMA            + 3500,
-      DIAG_UPPER_LIMIT         = DIAG_START_ANALYSIS        +  100
+      DIAG_START_COMMON        =                          0,
+      DIAG_START_DRIVER        = DIAG_START_COMMON        + DIAG_SIZE_COMMON,
+      DIAG_START_FRONTEND      = DIAG_START_DRIVER        + DIAG_SIZE_DRIVER,
+      DIAG_START_SERIALIZATION = DIAG_START_FRONTEND      + DIAG_SIZE_FRONTEND,
+      DIAG_START_LEX           = DIAG_START_SERIALIZATION + DIAG_SIZE_SERIALIZATION,
+      DIAG_START_PARSE         = DIAG_START_LEX           + DIAG_SIZE_LEX,
+      DIAG_START_AST           = DIAG_START_PARSE         + DIAG_SIZE_PARSE,
+      DIAG_START_COMMENT       = DIAG_START_AST           + DIAG_SIZE_AST,
+      DIAG_START_SEMA          = DIAG_START_COMMENT       + DIAG_SIZE_COMMENT,
+      DIAG_START_ANALYSIS      = DIAG_START_SEMA          + DIAG_SIZE_SEMA,
+      DIAG_UPPER_LIMIT         = DIAG_START_ANALYSIS      + DIAG_SIZE_ANALYSIS
     };
 
     class CustomDiagInfo;
Index: lib/Basic/DiagnosticIDs.cpp
===================================================================
--- lib/Basic/DiagnosticIDs.cpp
+++ lib/Basic/DiagnosticIDs.cpp
@@ -96,18 +96,6 @@
 /// GetDiagInfo - Return the StaticDiagInfoRec entry for the specified DiagID,
 /// or null if the ID is invalid.
 static const StaticDiagInfoRec *GetDiagInfo(unsigned DiagID) {
-  // If assertions are enabled, verify that the StaticDiagInfo array is sorted.
-#ifndef NDEBUG
-  static bool IsFirst = true; // So the check is only performed on first call.
-  if (IsFirst) {
-    assert(std::is_sorted(std::begin(StaticDiagInfo),
-                          std::end(StaticDiagInfo)) &&
-           "Diag ID conflict, the enums at the start of clang::diag (in "
-           "DiagnosticIDs.h) probably need to be increased");
-    IsFirst = false;
-  }
-#endif
-
   // Out of bounds diag. Can't be in the table.
   using namespace diag;
   if (DiagID >= DIAG_UPPER_LIMIT || DiagID <= DIAG_START_COMMON)
Index: test/Frontend/system-header-line-directive-ms-lineendings.c
===================================================================
--- test/Frontend/system-header-line-directive-ms-lineendings.c
+++ test/Frontend/system-header-line-directive-ms-lineendings.c
@@ -1,21 +1,21 @@
-// RUN: %clang_cc1 %s -E -o - -I %S/Inputs -isystem %S/Inputs/SystemHeaderPrefix | FileCheck %s
-#include <noline.h>
-#include <line-directive-in-system.h>
-
-#include "line-directive.h"
-
-// This tests that the line numbers for the current file are correctly outputted
-// for the include-file-completed test case.  
-
-// CHECK: # 1 "{{.*}}system-header-line-directive-ms-lineendings.c" 2
-// CHECK: # 1 "{{.*}}noline.h" 1 3
-// CHECK: foo();
-// CHECK: # 3 "{{.*}}system-header-line-directive-ms-lineendings.c" 2
-// CHECK: # 1 "{{.*}}line-directive-in-system.h" 1 3
-//      The "3" below indicates that "foo.h" is considered a system header.
-// CHECK: # 1 "foo.h" 3
-// CHECK: foo();
-// CHECK: # 4 "{{.*}}system-header-line-directive-ms-lineendings.c" 2
-// CHECK: # 1 "{{.*}}line-directive.h" 1
-// CHECK: # 10 "foo.h"{{$}}
-// CHECK: # 6 "{{.*}}system-header-line-directive-ms-lineendings.c" 2
+// RUN: %clang_cc1 %s -E -o - -I %S/Inputs -isystem %S/Inputs/SystemHeaderPrefix | FileCheck %s
+#include <noline.h>
+#include <line-directive-in-system.h>
+
+#include "line-directive.h"
+
+// This tests that the line numbers for the current file are correctly outputted
+// for the include-file-completed test case.  
+
+// CHECK: # 1 "{{.*}}system-header-line-directive-ms-lineendings.c" 2
+// CHECK: # 1 "{{.*}}noline.h" 1 3
+// CHECK: foo();
+// CHECK: # 3 "{{.*}}system-header-line-directive-ms-lineendings.c" 2
+// CHECK: # 1 "{{.*}}line-directive-in-system.h" 1 3
+//      The "3" below indicates that "foo.h" is considered a system header.
+// CHECK: # 1 "foo.h" 3
+// CHECK: foo();
+// CHECK: # 4 "{{.*}}system-header-line-directive-ms-lineendings.c" 2
+// CHECK: # 1 "{{.*}}line-directive.h" 1
+// CHECK: # 10 "foo.h"{{$}}
+// CHECK: # 6 "{{.*}}system-header-line-directive-ms-lineendings.c" 2