Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -883,7 +883,7 @@
 example, to collect options required to tune compilation for particular
 target, such as -L, -I, -l, --sysroot, codegen options, etc.
 
-The command line option `--config` can be used to specify configuration
+The command line option ``--config`` can be used to specify configuration
 file in a Clang invocation. For example:
 
 ::
@@ -906,17 +906,19 @@
 
 If no explicit configuration file is specified, Clang searches for a default
 configuration file following the rules described in the next paragraphs.
-To disable this behavior, `--no-default-config` flag can be used.
+To disable this behavior, ``--no-default-config`` flag can be used.
 
 Another way to specify a configuration file is to encode it in executable name.
-For example, if the Clang executable is named `armv7l-clang` (it may be a
-symbolic link to `clang`), then Clang will search for file `armv7l.cfg` in the
-directory where Clang resides.
+For example, if the Clang executable is named ``armv7l-clang`` (it may be a
+symbolic link to ``clang``), then Clang will search for file ``armv7l.cfg``
+in the directory where Clang resides. If Clang is started via an executable
+without target prefix, Clang will use ``default.cfg`` instead.
 
 If a driver mode is specified in invocation, Clang tries to find a file specific
 for the specified mode. For example, if the executable file is named
-`x86_64-clang-cl`, Clang first looks for `x86_64-cl.cfg` and if it is not found,
-looks for `x86_64.cfg`.
+``x86_64-clang-cl``, Clang first looks for ``x86_64-clang-cl.cfg`` and if it is
+not found, looks for ``x86_64.cfg``. Similarly, for ``clang-cl``, it looks for
+``default-clang-cl.cfg`` before trying ``default.cfg``.
 
 If the command line contains options that effectively change target architecture
 (these are -m32, -EL, and some others) and the configuration file starts with an
@@ -927,12 +929,12 @@
 
     x86_64-clang -m32 abc.c
 
-causes Clang search for a file `i368.cfg` first, and if no such file is found,
-Clang looks for the file `x86_64.cfg`.
+causes Clang search for a file ``i368.cfg`` first, and if no such file is found,
+Clang looks for the file ``x86_64.cfg``.
 
 The configuration file consists of command-line options specified on one or
 more lines. Lines composed of whitespace characters only are ignored as well as
-lines in which the first non-blank character is `#`. Long options may be split
+lines in which the first non-blank character is ``#``. Long options may be split
 between several lines by a trailing backslash. Here is example of a
 configuration file:
 
@@ -948,19 +950,19 @@
     # other config files may be included
     @linux.options
 
-Files included by `@file` directives in configuration files are resolved
+Files included by ``@file`` directives in configuration files are resolved
 relative to the including file. For example, if a configuration file
-`~/.llvm/target.cfg` contains the directive `@os/linux.opts`, the file
-`linux.opts` is searched for in the directory `~/.llvm/os`.
+``~/.llvm/target.cfg`` contains the directive ``@os/linux.opts``, the file
+``linux.opts`` is searched for in the directory ``~/.llvm/os``.
 
-To generate paths relative to the configuration file, the `<CFGDIR>` token may
+To generate paths relative to the configuration file, the ``<CFGDIR>`` token may
 be used. This will expand to the absolute path of the directory containing the
 configuration file.
 
 In cases where a configuration file is deployed alongside SDK contents, the
-SDK directory can remain fully portable by using `<CFGDIR>` prefixed paths.
+SDK directory can remain fully portable by using ``<CFGDIR>`` prefixed paths.
 In this way, the user may only need to specify a root configuration file with
-`--config` to establish every aspect of the SDK with the compiler:
+``--config`` to establish every aspect of the SDK with the compiler:
 
 ::
 
Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -1024,18 +1024,21 @@
     }
   }
 
-  if (!(CLOptions && CLOptions->hasArg(options::OPT_no_default_config))) {
+  if (CfgFileName.empty()) {
+    if (CLOptions && CLOptions->hasArg(options::OPT_no_default_config))
+      return false;
+
     // If config file is not specified explicitly, try to deduce configuration
     // from executable name. For instance, an executable 'armv7l-clang' will
-    // search for config file 'armv7l-clang.cfg'.
-    if (CfgFileName.empty() && !ClangNameParts.TargetPrefix.empty())
+    // search for config file 'armv7l-clang.cfg'. If we are called without
+    // a specific prefix, use e.g. 'default-clang.cfg' instead.
+    if (!ClangNameParts.TargetPrefix.empty())
       CfgFileName =
           ClangNameParts.TargetPrefix + '-' + ClangNameParts.ModeSuffix;
+    else
+      CfgFileName = "default-" + ClangNameParts.ModeSuffix;
   }
 
-  if (CfgFileName.empty())
-    return false;
-
   // Determine architecture part of the file name, if it is present.
   StringRef CfgFileArch = CfgFileName;
   size_t ArchPrefixLen = CfgFileArch.find('-');
@@ -1093,9 +1096,9 @@
     return readConfigFile(CfgFilePath);
 
   // Finally try removing driver mode part: 'x86_64-clang.cfg' -> 'x86_64.cfg'.
-  if (!ClangNameParts.ModeSuffix.empty() &&
-      !ClangNameParts.TargetPrefix.empty()) {
-    CfgFileName.assign(ClangNameParts.TargetPrefix);
+  if (!FileSpecifiedExplicitly && !ClangNameParts.ModeSuffix.empty()) {
+    CfgFileName.resize(CfgFileName.size() - ClangNameParts.ModeSuffix.size() -
+                       5);
     CfgFileName.append(".cfg");
     if (searchForFile(CfgFilePath, CfgFileSearchDirs, CfgFileName, getVFS()))
       return readConfigFile(CfgFilePath);
Index: clang/test/Driver/config-file3.c
===================================================================
--- clang/test/Driver/config-file3.c
+++ clang/test/Driver/config-file3.c
@@ -21,6 +21,10 @@
 // RUN: ln -s %clang %t/testdmode/qqq-clang-g++
 // RUN: echo "-Wundefined-func-template" > %t/testdmode/qqq-clang-g++.cfg
 // RUN: echo "-Werror" > %t/testdmode/qqq.cfg
+// RUN: ln -s %clang %t/testdmode/clang-g++
+// RUN: ln -s %clang %t/testdmode/clang
+// RUN: : > %t/testdmode/default-clang.cfg
+// RUN: : > %t/testdmode/default.cfg
 // RUN: %t/testdmode/qqq-clang-g++ --config-system-dir= --config-user-dir= -c -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix FULL-NAME
 //
 // FULL-NAME: Configuration file: {{.*}}/testdmode/qqq-clang-g++.cfg
@@ -41,6 +45,16 @@
 //
 // CHECK-EXPLICIT: Configuration file: {{.*}}/Inputs/config/i386-qqq.cfg
 
+//--- Invoking clang falls back to default-clang.cfg.
+// RUN: %t/testdmode/clang --config-system-dir= --config-user-dir= -c -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix DEFAULT-CLANG
+//
+// DEFAULT-CLANG: Configuration file: {{.*}}/testdmode/default-clang.cfg
+
+//--- Invoking clang-g++ falls back to default.cfg.
+// RUN: %t/testdmode/clang-g++ --config-system-dir= --config-user-dir= -c -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix DEFAULT
+//
+// DEFAULT: Configuration file: {{.*}}/testdmode/default.cfg
+
 //--- --no-default-config disables config search.
 //
 // RUN: %t/testdmode/qqq-clang-g++ --config-system-dir= --config-user-dir=%t/testdmode --no-default-config -c -### %s 2>&1 | FileCheck %s -check-prefix NO-DEFAULT-CONFIG