5 files changed, 56 insertions, 21 deletions

diff --git a/lib/Lex/ModuleMap.cpp b/lib/Lex/ModuleMap.cpp
index 0c03201aa6..1458a73a7d 100644
--- a/lib/Lex/ModuleMap.cpp
+++ b/lib/Lex/ModuleMap.cpp
@@ -149,6 +149,24 @@ static StringRef sanitizeFilenameAsIdentifier(StringRef Name,
   return Name;
 }
 
+/// \brief Determine whether the given file name is the name of a builtin
+/// header, supplied by Clang to replace, override, or augment existing system
+/// headers.
+static bool isBuiltinHeader(StringRef FileName) {
+  return llvm::StringSwitch<bool>(FileName)
+           .Case("float.h", true)
+           .Case("iso646.h", true)
+           .Case("limits.h", true)
+           .Case("stdalign.h", true)
+           .Case("stdarg.h", true)
+           .Case("stdbool.h", true)
+           .Case("stddef.h", true)
+           .Case("stdint.h", true)
+           .Case("tgmath.h", true)
+           .Case("unwind.h", true)
+           .Default(false);
+}
+
 Module *ModuleMap::findModuleForHeader(const FileEntry *File) {
   HeadersMap::iterator Known = Headers.find(File);
   if (Known != Headers.end()) {
@@ -158,6 +176,25 @@ Module *ModuleMap::findModuleForHeader(const FileEntry *File) {
 
     return Known->second.getModule();
   }
+
+  // If we've found a builtin header within Clang's builtin include directory,
+  // load all of the module maps to see if it will get associated with a
+  // specific module (e.g., in /usr/include).
+  if (File->getDir() == BuiltinIncludeDir &&
+      isBuiltinHeader(llvm::sys::path::filename(File->getName()))) {
+    SmallVector<Module *, 4> AllModules;
+    HeaderInfo.collectAllModules(AllModules);
+
+    // Check again.
+    Known = Headers.find(File);
+    if (Known != Headers.end()) {
+      // If a header is not available, don't report that it maps to anything.
+      if (!Known->second.isAvailable())
+        return 0;
+
+      return Known->second.getModule();
+    }
+  }
   
   const DirectoryEntry *Dir = File->getDir();
   SmallVector<const DirectoryEntry *, 2> SkippedDirs;
@@ -1266,24 +1303,6 @@ static void appendSubframeworkPaths(Module *Mod,
   }
 }
 
-/// \brief Determine whether the given file name is the name of a builtin
-/// header, supplied by Clang to replace, override, or augment existing system
-/// headers.
-static bool isBuiltinHeader(StringRef FileName) {
-  return llvm::StringSwitch<bool>(FileName)
-      .Case("float.h", true)
-      .Case("iso646.h", true)
-      .Case("limits.h", true)
-      .Case("stdalign.h", true)
-      .Case("stdarg.h", true)
-      .Case("stdbool.h", true)
-      .Case("stddef.h", true)
-      .Case("stdint.h", true)
-      .Case("tgmath.h", true)
-      .Case("unwind.h", true)
-      .Default(false);
-}
-
 /// \brief Parse a header declaration.
 ///
 ///   header-declaration:
diff --git a/test/Modules/Inputs/System/usr/include/dbl_max.h b/test/Modules/Inputs/System/usr/include/dbl_max.h
new file mode 100644
index 0000000000..9a020d1bf5
--- /dev/null
+++ b/test/Modules/Inputs/System/usr/include/dbl_max.h
@@ -0,0 +1 @@
+#define DBL_MAX __DBL_MAX__
diff --git a/test/Modules/Inputs/System/usr/include/module.map b/test/Modules/Inputs/System/usr/include/module.map
index 884b59c80c..9b2f3af2ba 100644
--- a/test/Modules/Inputs/System/usr/include/module.map
+++ b/test/Modules/Inputs/System/usr/include/module.map
@@ -19,3 +19,14 @@ module cstd [system] {
     header "stdint.h"
   }
 }
+
+module other_constants {
+  explicit module dbl_max {
+    header "dbl_max.h"
+  }
+}
+
+module uses_other_constants {
+  header "uses_other_constants.h"
+  export *
+}
diff --git a/test/Modules/Inputs/System/usr/include/uses_other_constants.h b/test/Modules/Inputs/System/usr/include/uses_other_constants.h
new file mode 100644
index 0000000000..f6d4cca9f8
--- /dev/null
+++ b/test/Modules/Inputs/System/usr/include/uses_other_constants.h
@@ -0,0 +1,3 @@
+@import other_constants;
+#include <float.h>
+
diff --git a/test/Modules/cstd.m b/test/Modules/cstd.m
index 6d896a9155..3d1dcf38e3 100644
--- a/test/Modules/cstd.m
+++ b/test/Modules/cstd.m
@@ -1,6 +1,9 @@
 // RUN: rm -rf %t
 // RUN: %clang -fsyntax-only -isystem %S/Inputs/System/usr/include -fmodules -fmodules-cache-path=%t -D__need_wint_t -Werror=implicit-function-declaration %s
 
+@import uses_other_constants;
+const double other_value = DBL_MAX;
+
 // Supplied by compiler, but referenced from the "/usr/include" module map.
 @import cstd.float_constants;
 
@@ -16,7 +19,7 @@ void test_fprintf(FILE *file) {
 // Supplied by compiler, which forwards to the "/usr/include" version.
 @import cstd.stdint;
 
-my_awesome_nonstandard_integer_type value;
+my_awesome_nonstandard_integer_type value2;
 
 // Supplied by the compiler; that version wins.
 @import cstd.stdbool;
@@ -25,5 +28,3 @@ my_awesome_nonstandard_integer_type value;
 #  error "bool was not defined!"
 #endif
 
-
-