diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index 8753589..c1f85c1 100644
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -380,6 +380,9 @@
 // DefaultIgnore in addition to putting it here.
 def : DiagGroup<"all", [Most, Parentheses, Switch]>;
 
+// Warnings enabled by -pedantic.  This is magically filled in by TableGen.
+def Pedantic : DiagGroup<"pedantic">;
+
 // Aliases.
 def : DiagGroup<"", [Extra]>;                   // -W = -Wextra
 def : DiagGroup<"endif-labels", [ExtraTokens]>; // -Wendif-labels=-Wendif-tokens
diff --git a/include/clang/Driver/Options.td b/include/clang/Driver/Options.td
index 48f9cd6..918718a 100644
--- a/include/clang/Driver/Options.td
+++ b/include/clang/Driver/Options.td
@@ -868,6 +868,7 @@
 def no_cpp_precomp : Flag<"-no-cpp-precomp">, Group<clang_ignored_f_Group>;
 def no_integrated_as : Flag<"-no-integrated-as">, Flags<[DriverOption]>;
 def no_integrated_cpp : Flag<"-no-integrated-cpp">, Flags<[DriverOption]>;
+def no_pedantic : Flag<"-no-pedantic">, Group<pedantic_Group>;
 def no__dead__strip__inits__and__terms : Flag<"-no_dead_strip_inits_and_terms">;
 def nobuiltininc : Flag<"-nobuiltininc">, Flags<[CC1Option]>,
   HelpText<"Disable builtin #include directories">;
@@ -1070,6 +1071,7 @@
 def _machine : Separate<"--machine">, Alias<m_Joined>;
 def _no_integrated_cpp : Flag<"--no-integrated-cpp">, Alias<no_integrated_cpp>;
 def _no_line_commands : Flag<"--no-line-commands">, Alias<P>;
+def _no_pedantic : Flag<"--no-pedantic">, Alias<no_pedantic>;
 def _no_standard_includes : Flag<"--no-standard-includes">, Alias<nostdinc>;
 def _no_standard_libraries : Flag<"--no-standard-libraries">, Alias<nostdlib>;
 def _no_undefined : Flag<"--no-undefined">, Flags<[LinkerInput]>;
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index dd198a1..66d792f 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -2093,7 +2093,8 @@
   }
 
   Args.AddAllArgs(CmdArgs, options::OPT_W_Group);
-  Args.AddLastArg(CmdArgs, options::OPT_pedantic);
+  if (Args.hasFlag(options::OPT_pedantic, options::OPT_no_pedantic, false))
+    CmdArgs.push_back("-pedantic");
   Args.AddLastArg(CmdArgs, options::OPT_pedantic_errors);
   Args.AddLastArg(CmdArgs, options::OPT_w);
 
diff --git a/lib/Frontend/TextDiagnosticPrinter.cpp b/lib/Frontend/TextDiagnosticPrinter.cpp
index d07917f..30da72b 100644
--- a/lib/Frontend/TextDiagnosticPrinter.cpp
+++ b/lib/Frontend/TextDiagnosticPrinter.cpp
@@ -79,16 +79,6 @@
       Started = true;
     }
 
-    // If the diagnostic is an extension diagnostic and not enabled by default
-    // then it must have been turned on with -pedantic.
-    bool EnabledByDefault;
-    if (DiagnosticIDs::isBuiltinExtensionDiag(Info.getID(),
-                                              EnabledByDefault) &&
-        !EnabledByDefault) {
-      OS << (Started ? "," : " [") << "-pedantic";
-      Started = true;
-    }
-
     StringRef Opt = DiagnosticIDs::getWarningOptionForDiag(Info.getID());
     if (!Opt.empty()) {
       OS << (Started ? "," : " [") << "-W" << Opt;
diff --git a/test/Driver/warning-options.cpp b/test/Driver/warning-options.cpp
index ce434ab..7b1b097 100644
--- a/test/Driver/warning-options.cpp
+++ b/test/Driver/warning-options.cpp
@@ -8,3 +8,11 @@
 // CHECK: unknown warning option '-Wmonkey'
 // CHECK: unknown warning option '-Wno-monkey'
 // CHECK: unknown warning option '-Wno-unused-command-line-arguments'; did you mean '-Wno-unused-command-line-argument'?
+
+// RUN: %clang -### -pedantic -no-pedantic %s 2>&1 | FileCheck -check-prefix=NO_PEDANTIC %s
+// RUN: %clang -### -pedantic -Wno-pedantic %s 2>&1 | FileCheck -check-prefix=PEDANTIC %s
+// NO_PEDANTIC-NOT: -pedantic
+// RUN: %clang -### -pedantic -pedantic -no-pedantic -pedantic %s 2>&1 | FileCheck -check-prefix=PEDANTIC %s
+// RUN: %clang -### -pedantic -pedantic -no-pedantic -Wpedantic %s 2>&1 | FileCheck -check-prefix=PEDANTIC %s
+// PEDANTIC: -pedantic
+
diff --git a/test/Misc/show-diag-options.c b/test/Misc/show-diag-options.c
index f0404a8..ef0a5a6 100644
--- a/test/Misc/show-diag-options.c
+++ b/test/Misc/show-diag-options.c
@@ -23,5 +23,5 @@
   // OPTION_ERROR_CATEGORY: {{.*}}: error: {{[a-z ]+}} [-Werror,-Wparentheses,Semantic Issue]
 
   // Leverage the fact that all these '//'s get warned about in C89 pedantic.
-  // OPTION_PEDANTIC: {{.*}}: warning: {{[/a-z ]+}} [-pedantic,-Wcomment]
+  // OPTION_PEDANTIC: {{.*}}: warning: {{[/a-z ]+}} [-Wcomment]
 }
diff --git a/test/Misc/warning-flags.c b/test/Misc/warning-flags.c
index 99ebf99..15b2d27 100644
--- a/test/Misc/warning-flags.c
+++ b/test/Misc/warning-flags.c
@@ -17,66 +17,7 @@
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (229):
-CHECK-NEXT:   ext_anonymous_struct_union_qualified
-CHECK-NEXT:   ext_binary_literal
-CHECK-NEXT:   ext_cast_fn_obj
-CHECK-NEXT:   ext_delete_void_ptr_operand
-CHECK-NEXT:   ext_designated_init
-CHECK-NEXT:   ext_duplicate_declspec
-CHECK-NEXT:   ext_ellipsis_exception_spec
-CHECK-NEXT:   ext_enum_friend
-CHECK-NEXT:   ext_enum_value_not_int
-CHECK-NEXT:   ext_enumerator_list_comma
-CHECK-NEXT:   ext_expected_semi_decl_list
-CHECK-NEXT:   ext_explicit_instantiation_without_qualified_id
-CHECK-NEXT:   ext_explicit_specialization_storage_class
-CHECK-NEXT:   ext_forward_ref_enum
-CHECK-NEXT:   ext_freestanding_complex
-CHECK-NEXT:   ext_hexconstant_invalid
-CHECK-NEXT:   ext_ident_list_in_param
-CHECK-NEXT:   ext_imaginary_constant
-CHECK-NEXT:   ext_implicit_lib_function_decl
-CHECK-NEXT:   ext_in_class_initializer_non_constant
-CHECK-NEXT:   ext_integer_complement_complex
-CHECK-NEXT:   ext_integer_complex
-CHECK-NEXT:   ext_integer_increment_complex
-CHECK-NEXT:   ext_invalid_sign_spec
-CHECK-NEXT:   ext_missing_declspec
-CHECK-NEXT:   ext_missing_whitespace_after_macro_name
-CHECK-NEXT:   ext_new_paren_array_nonconst
-CHECK-NEXT:   ext_nonstandard_escape
-CHECK-NEXT:   ext_param_not_declared
-CHECK-NEXT:   ext_plain_complex
-CHECK-NEXT:   ext_pp_bad_vaargs_use
-CHECK-NEXT:   ext_pp_comma_expr
-CHECK-NEXT:   ext_pp_ident_directive
-CHECK-NEXT:   ext_pp_include_next_directive
-CHECK-NEXT:   ext_pp_line_too_big
-CHECK-NEXT:   ext_pp_macro_redef
-CHECK-NEXT:   ext_pp_warning_directive
-CHECK-NEXT:   ext_return_has_void_expr
-CHECK-NEXT:   ext_subscript_non_lvalue
-CHECK-NEXT:   ext_template_arg_extra_parens
-CHECK-NEXT:   ext_thread_before
-CHECK-NEXT:   ext_typecheck_addrof_void
-CHECK-NEXT:   ext_typecheck_cast_nonscalar
-CHECK-NEXT:   ext_typecheck_cast_to_union
-CHECK-NEXT:   ext_typecheck_comparison_of_distinct_pointers
-CHECK-NEXT:   ext_typecheck_comparison_of_distinct_pointers_nonstandard
-CHECK-NEXT:   ext_typecheck_comparison_of_fptr_to_void
-CHECK-NEXT:   ext_typecheck_comparison_of_pointer_integer
-CHECK-NEXT:   ext_typecheck_cond_incompatible_operands
-CHECK-NEXT:   ext_typecheck_cond_incompatible_operands_nonstandard
-CHECK-NEXT:   ext_typecheck_cond_one_void
-CHECK-NEXT:   ext_typecheck_convert_pointer_void_func
-CHECK-NEXT:   ext_typecheck_ordered_comparison_of_function_pointers
-CHECK-NEXT:   ext_typecheck_ordered_comparison_of_pointer_and_zero
-CHECK-NEXT:   ext_typecheck_ordered_comparison_of_pointer_integer
-CHECK-NEXT:   ext_typecheck_zero_array_size
-CHECK-NEXT:   ext_unknown_escape
-CHECK-NEXT:   ext_using_undefined_std
-CHECK-NEXT:   ext_vla_folded_to_constant
+CHECK: Warnings without flags (158):
 CHECK-NEXT:   pp_include_next_absolute_path
 CHECK-NEXT:   pp_include_next_in_primary
 CHECK-NEXT:   pp_invalid_string_literal
@@ -138,9 +79,6 @@
 CHECK-NEXT:   warn_enum_value_overflow
 CHECK-NEXT:   warn_enumerator_too_large
 CHECK-NEXT:   warn_exception_caught_by_earlier_handler
-CHECK-NEXT:   warn_excess_initializers
-CHECK-NEXT:   warn_excess_initializers_in_char_array_initializer
-CHECK-NEXT:   warn_expected_qualified_after_typename
 CHECK-NEXT:   warn_extraneous_char_constant
 CHECK-NEXT:   warn_fe_cc_log_diagnostics_failure
 CHECK-NEXT:   warn_fe_cc_print_header_failure
@@ -149,23 +87,17 @@
 CHECK-NEXT:   warn_function_attribute_wrong_type
 CHECK-NEXT:   warn_gc_attribute_weak_on_local
 CHECK-NEXT:   warn_gnu_inline_attribute_requires_inline
-CHECK-NEXT:   warn_hex_escape_too_large
 CHECK-NEXT:   warn_ignoring_ftabstop_value
-CHECK-NEXT:   warn_illegal_constant_array_size
 CHECK-NEXT:   warn_implements_nscopying
 CHECK-NEXT:   warn_incompatible_qualified_id
-CHECK-NEXT:   warn_initializer_string_for_char_array_too_long
 CHECK-NEXT:   warn_inline_namespace_reopened_noninline
 CHECK-NEXT:   warn_integer_too_large
 CHECK-NEXT:   warn_integer_too_large_for_signed
 CHECK-NEXT:   warn_invalid_asm_cast_lvalue
-CHECK-NEXT:   warn_many_braces_around_scalar_init
 CHECK-NEXT:   warn_maynot_respond
 CHECK-NEXT:   warn_member_extra_qualification
 CHECK-NEXT:   warn_method_param_redefinition
-CHECK-NEXT:   warn_mismatched_exception_spec
 CHECK-NEXT:   warn_missing_case_for_condition
-CHECK-NEXT:   warn_missing_dependent_template_keyword
 CHECK-NEXT:   warn_missing_exception_specification
 CHECK-NEXT:   warn_missing_whitespace_after_macro_name
 CHECK-NEXT:   warn_multiple_method_decl
@@ -177,10 +109,8 @@
 CHECK-NEXT:   warn_objc_object_attribute_wrong_type
 CHECK-NEXT:   warn_objc_property_copy_missing_on_block
 CHECK-NEXT:   warn_objc_protocol_qualifier_missing_id
-CHECK-NEXT:   warn_octal_escape_too_large
 CHECK-NEXT:   warn_odr_tag_type_inconsistent
 CHECK-NEXT:   warn_on_superclass_use
-CHECK-NEXT:   warn_param_default_argument_redefinition
 CHECK-NEXT:   warn_partial_specs_not_deducible
 CHECK-NEXT:   warn_pointer_attribute_wrong_type
 CHECK-NEXT:   warn_pp_convert_lhs_to_positive
@@ -228,7 +158,6 @@
 CHECK-NEXT:   warn_second_parameter_to_va_arg_never_compatible
 CHECK-NEXT:   warn_standalone_specifier
 CHECK-NEXT:   warn_static_inline_explicit_inst_ignored
-CHECK-NEXT:   warn_static_non_static
 CHECK-NEXT:   warn_template_export_unsupported
 CHECK-NEXT:   warn_template_spec_extra_headers
 CHECK-NEXT:   warn_tentative_incomplete_array
@@ -247,3 +176,4 @@
 CHECK-NEXT:   warn_use_out_of_scope_declaration
 CHECK-NEXT:   warn_weak_identifier_undeclared
 CHECK-NEXT:   warn_weak_import
+
diff --git a/tools/libclang/CXStoredDiagnostic.cpp b/tools/libclang/CXStoredDiagnostic.cpp
index 8284dc9..fa331de 100644
--- a/tools/libclang/CXStoredDiagnostic.cpp
+++ b/tools/libclang/CXStoredDiagnostic.cpp
@@ -66,13 +66,8 @@
       *Disable = createCXString("-ferror-limit=0");
     return createCXString("-ferror-limit=");
   }
-  
-  bool EnabledByDefault;
-  if (DiagnosticIDs::isBuiltinExtensionDiag(ID, EnabledByDefault) &&
-      !EnabledByDefault)
-    return createCXString("-pedantic");
 
-  return createCXString("");  
+  return createCXString("");
 }
 
 unsigned CXStoredDiagnostic::getCategory() const {
diff --git a/utils/TableGen/ClangDiagnosticsEmitter.cpp b/utils/TableGen/ClangDiagnosticsEmitter.cpp
index 2df7ca9..4c480ec 100644
--- a/utils/TableGen/ClangDiagnosticsEmitter.cpp
+++ b/utils/TableGen/ClangDiagnosticsEmitter.cpp
@@ -11,9 +11,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/TableGen/Record.h"
@@ -78,7 +80,7 @@
                                                    DiagGroupParents);
     if (!CatName.empty()) return CatName;
   }
-  
+
   // If the diagnostic itself has a category, get it.
   return R->getValueAsString("CategoryName");
 }
@@ -160,6 +162,179 @@
 }
 
 //===----------------------------------------------------------------------===//
+// Infer members of -Wpedantic.
+//===----------------------------------------------------------------------===//
+
+typedef std::vector<const Record *> RecordVec;
+typedef llvm::DenseSet<const Record *> RecordSet;
+typedef llvm::PointerUnion<RecordVec*, RecordSet*> VecOrSet;
+
+namespace {
+class InferPedantic {
+  typedef llvm::DenseMap<const Record*,
+                         std::pair<unsigned, llvm::Optional<unsigned> > > GMap;
+
+  DiagGroupParentMap &DiagGroupParents;
+  const std::vector<Record*> &Diags;
+  const std::vector<Record*> DiagGroups;
+  std::map<std::string, GroupInfo> &DiagsInGroup;
+  llvm::DenseSet<const Record*> DiagsSet;
+  GMap GroupCount;
+public:
+  InferPedantic(DiagGroupParentMap &DiagGroupParents,
+                const std::vector<Record*> &Diags,
+                const std::vector<Record*> &DiagGroups,
+                std::map<std::string, GroupInfo> &DiagsInGroup)
+  : DiagGroupParents(DiagGroupParents),
+  Diags(Diags),
+  DiagGroups(DiagGroups),
+  DiagsInGroup(DiagsInGroup) {}
+
+  /// Compute the set of diagnostics and groups that are immediately
+  /// in -Wpedantic.
+  void compute(VecOrSet DiagsInPedantic,
+               VecOrSet GroupsInPedantic);
+
+private:
+  /// Determine whether a group is a subgroup of another group.
+  bool isSubGroupOfGroup(const Record *Group,
+                         llvm::StringRef RootGroupName);
+
+  /// Determine if the diagnostic is an extension.
+  bool isExtension(const Record *Diag);
+
+  /// Increment the count for a group, and transitively marked
+  /// parent groups when appropriate.
+  void markGroup(const Record *Group);
+
+  /// Return true if the diagnostic is in a pedantic group.
+  bool groupInPedantic(const Record *Group, bool increment = false);
+};
+} // end anonymous namespace
+
+bool InferPedantic::isSubGroupOfGroup(const Record *Group,
+                                      llvm::StringRef GName) {
+
+  const std::string &GroupName = Group->getValueAsString("GroupName");
+  if (GName == GroupName)
+    return true;
+
+  const std::vector<Record*> &Parents = DiagGroupParents.getParents(Group);
+  for (unsigned i = 0, e = Parents.size(); i != e; ++i)
+    if (isSubGroupOfGroup(Parents[i], GName))
+      return true;
+
+  return false;
+}
+
+/// Determine if the diagnostic is an extension.
+bool InferPedantic::isExtension(const Record *Diag) {
+  const std::string &ClsName = Diag->getValueAsDef("Class")->getName();
+  return ClsName == "CLASS_EXTENSION";
+}
+
+bool InferPedantic::groupInPedantic(const Record *Group, bool increment) {
+  GMap::mapped_type &V = GroupCount[Group];
+  // Lazily compute the threshold value for the group count.
+  if (!V.second.hasValue()) {
+    const GroupInfo &GI = DiagsInGroup[Group->getValueAsString("GroupName")];
+    V.second = GI.SubGroups.size() + GI.DiagsInGroup.size();
+  }
+
+  if (increment)
+    ++V.first;
+
+  // Consider a group in -Wpendatic IFF if has at least one diagnostic
+  // or subgroup AND all of those diagnostics and subgroups are covered
+  // by -Wpedantic via our computation.
+  return V.first != 0 && V.first == V.second.getValue();
+}
+
+void InferPedantic::markGroup(const Record *Group) {
+  // If all the diagnostics and subgroups have been marked as being
+  // covered by -Wpedantic, increment the count of parent groups.  Once the
+  // group's count is equal to the number of subgroups and diagnostics in
+  // that group, we can safely add this group to -Wpedantic.
+  if (groupInPedantic(Group, /* increment */ true)) {
+    const std::vector<Record*> &Parents = DiagGroupParents.getParents(Group);
+    for (unsigned i = 0, e = Parents.size(); i != e; ++i)
+      markGroup(Parents[i]);
+  }
+}
+
+void InferPedantic::compute(VecOrSet DiagsInPedantic,
+                            VecOrSet GroupsInPedantic) {
+  // All extensions are implicitly in the "pedantic" group.  For those that
+  // aren't explicitly included in -Wpedantic, mark them for consideration
+  // to be included in -Wpedantic directly.
+  for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
+    Record *R = Diags[i];
+    if (isExtension(R))
+      DiagsSet.insert(R);
+    if (DefInit *Group = dynamic_cast<DefInit*>(R->getValueInit("Group"))) {
+      const Record *GroupRec = Group->getDef();
+      if (!isSubGroupOfGroup(GroupRec, "pedantic")) {
+        markGroup(GroupRec);
+      }
+    }
+  }
+
+  // Compute the set of diagnostics that are directly in -Wpedantic.  We
+  // march through Diags a second time to ensure the results are emitted
+  // in deterministic order.
+  for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
+    Record *R = Diags[i];
+    if (!DiagsSet.count(R))
+      continue;
+    // Check if the group is implicitly in -Wpedantic.  If so,
+    // the diagnostic should not be directly included in the -Wpedantic
+    // diagnostic group.
+    if (DefInit *Group = dynamic_cast<DefInit*>(R->getValueInit("Group")))
+      if (groupInPedantic(Group->getDef()))
+        continue;
+
+    // The diagnostic is not included in a group that is (transitively) in
+    // -Wpedantic.  Include it in -Wpedantic directly.
+    if (RecordVec *V = DiagsInPedantic.dyn_cast<RecordVec*>())
+      V->push_back(R);
+    else {
+      DiagsInPedantic.get<RecordSet*>()->insert(R);
+    }
+  }
+
+  if (!GroupsInPedantic)
+    return;
+
+  // Compute the set of groups that are directly in -Wpedantic.  We
+  // march through the groups to ensure the results are emitted
+  /// in a deterministc order.
+  for (unsigned i = 0, ei = DiagGroups.size(); i != ei; ++i) {
+    Record *Group = DiagGroups[i];
+    if (!groupInPedantic(Group))
+      continue;
+
+    unsigned ParentsInPedantic = 0;
+    const std::vector<Record*> &Parents = DiagGroupParents.getParents(Group);
+    for (unsigned j = 0, ej = Parents.size(); j != ej; ++j) {
+      if (groupInPedantic(Parents[j]))
+        ++ParentsInPedantic;
+    }
+    // If all the parents are in -Wpedantic, this means that this diagnostic
+    // group will be indirectly included by -Wpedantic already.  In that
+    // case, do not add it directly to -Wpedantic.  If the group has no
+    // parents, obviously it should go into -Wpedantic.
+    if (Parents.size() > 0 && ParentsInPedantic == Parents.size())
+      continue;
+
+    if (RecordVec *V = GroupsInPedantic.dyn_cast<RecordVec*>())
+      V->push_back(Group);
+    else {
+      GroupsInPedantic.get<RecordSet*>()->insert(Group);
+    }
+  }
+}
+
+//===----------------------------------------------------------------------===//
 // Warning Tables (.inc file) generation.
 //===----------------------------------------------------------------------===//
 
@@ -190,6 +365,11 @@
   DiagCategoryIDMap CategoryIDs(Records);
   DiagGroupParentMap DGParentMap(Records);
 
+  // Compute the set of diagnostics that are in -Wpedantic.
+  RecordSet DiagsInPedantic;
+  InferPedantic inferPedantic(DGParentMap, Diags, DiagGroups, DiagsInGroup);
+  inferPedantic.compute(&DiagsInPedantic, (RecordVec*)0);
+
   for (unsigned i = 0, e = Diags.size(); i != e; ++i) {
     const Record &R = *Diags[i];
     // Filter by component.
@@ -211,6 +391,11 @@
           DiagsInGroup.find(DI->getDef()->getValueAsString("GroupName"));
       assert(I != DiagsInGroup.end());
       OS << ", " << I->second.IDNo;
+    } else if (DiagsInPedantic.count(&R)) {
+      std::map<std::string, GroupInfo>::iterator I =
+        DiagsInGroup.find("pedantic");
+      assert(I != DiagsInGroup.end() && "pedantic group not defined");
+      OS << ", " << I->second.IDNo;
     } else {
       OS << ", 0";
     }
@@ -262,12 +447,12 @@
     enumName += isalnum(*I) ? *I : '_';
   return enumName.str();
 }
-
+  
 namespace clang {
 void EmitClangDiagGroups(RecordKeeper &Records, raw_ostream &OS) {
   // Compute a mapping from a DiagGroup to all of its parents.
   DiagGroupParentMap DGParentMap(Records);
-  
+
   std::vector<Record*> Diags =
     Records.getAllDerivedDefinitions("Diagnostic");
   
@@ -276,7 +461,15 @@
 
   std::map<std::string, GroupInfo> DiagsInGroup;
   groupDiagnostics(Diags, DiagGroups, DiagsInGroup);
-  
+
+  // All extensions are implicitly in the "pedantic" group.  Record the
+  // implicit set of groups in the "pedantic" group, and use this information
+  // later when emitting the group information for Pedantic.
+  RecordVec DiagsInPedantic;
+  RecordVec GroupsInPedantic;
+  InferPedantic inferPedantic(DGParentMap, Diags, DiagGroups, DiagsInGroup);
+  inferPedantic.compute(&DiagsInPedantic, &GroupsInPedantic);
+
   // Walk through the groups emitting an array for each diagnostic of the diags
   // that are mapped to.
   OS << "\n#ifdef GET_DIAG_ARRAYS\n";
@@ -284,17 +477,23 @@
   for (std::map<std::string, GroupInfo>::iterator
        I = DiagsInGroup.begin(), E = DiagsInGroup.end(); I != E; ++I) {
     MaxLen = std::max(MaxLen, (unsigned)I->first.size());
-    
+    const bool IsPedantic = I->first == "pedantic";
+
     std::vector<const Record*> &V = I->second.DiagsInGroup;
-    if (!V.empty()) {
+    if (!V.empty() || (IsPedantic && !DiagsInPedantic.empty())) {
       OS << "static const short DiagArray" << I->second.IDNo << "[] = { ";
       for (unsigned i = 0, e = V.size(); i != e; ++i)
         OS << "diag::" << V[i]->getName() << ", ";
+      // Emit the diagnostics implicitly in "pedantic".
+      if (IsPedantic) {
+        for (unsigned i = 0, e = DiagsInPedantic.size(); i != e; ++i)
+          OS << "diag::" << DiagsInPedantic[i]->getName() << ", ";
+      }
       OS << "-1 };\n";
     }
     
     const std::vector<std::string> &SubGroups = I->second.SubGroups;
-    if (!SubGroups.empty()) {
+    if (!SubGroups.empty() || (IsPedantic && !GroupsInPedantic.empty())) {
       OS << "static const short DiagSubGroup" << I->second.IDNo << "[] = { ";
       for (unsigned i = 0, e = SubGroups.size(); i != e; ++i) {
         std::map<std::string, GroupInfo>::iterator RI =
@@ -302,6 +501,18 @@
         assert(RI != DiagsInGroup.end() && "Referenced without existing?");
         OS << RI->second.IDNo << ", ";
       }
+      // Emit the groups implicitly in "pedantic".
+      if (IsPedantic) {
+        for (unsigned i = 0, e = GroupsInPedantic.size(); i != e; ++i) {
+          const std::string &GroupName =
+            GroupsInPedantic[i]->getValueAsString("GroupName");
+          std::map<std::string, GroupInfo>::iterator RI =
+            DiagsInGroup.find(GroupName);
+          assert(RI != DiagsInGroup.end() && "Referenced without existing?");
+          OS << RI->second.IDNo << ", ";
+        }
+      }
+
       OS << "-1 };\n";
     }
   }
@@ -321,15 +532,22 @@
       throw "Invalid character in diagnostic group '" + I->first + "'";
     OS.write_escaped(I->first) << "\","
                                << std::string(MaxLen-I->first.size()+1, ' ');
-    
+
+    // Special handling for 'pedantic'.
+    const bool IsPedantic = I->first == "pedantic";
+
     // Diagnostics in the group.
-    if (I->second.DiagsInGroup.empty())
+    const bool hasDiags = !I->second.DiagsInGroup.empty() ||
+                          (IsPedantic && !DiagsInPedantic.empty());
+    if (!hasDiags)
       OS << "0, ";
     else
       OS << "DiagArray" << I->second.IDNo << ", ";
     
     // Subgroups.
-    if (I->second.SubGroups.empty())
+    const bool hasSubGroups = !I->second.SubGroups.empty() ||
+                              (IsPedantic && !GroupsInPedantic.empty());
+    if (!hasSubGroups)
       OS << 0;
     else
       OS << "DiagSubGroup" << I->second.IDNo;