diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 013d5b32074e9e..52990f14e7eac4 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -964,7 +964,6 @@ bool Driver::readConfigFile(StringRef FileName) {
 
 bool Driver::loadConfigFile() {
   std::string CfgFileName;
-  bool FileSpecifiedExplicitly = false;
 
   // Process options that change search path for config files.
   if (CLOptions) {
@@ -988,7 +987,11 @@ bool Driver::loadConfigFile() {
     }
   }
 
+  // Prepare list of directories where config file is searched for.
+  StringRef CfgFileSearchDirs[] = {UserConfigDir, SystemConfigDir, Dir};
+
   // First try to find config file specified in command line.
+  llvm::SmallString<128> CfgFilePath;
   if (CLOptions) {
     std::vector<std::string> ConfigFiles =
         CLOptions->getAllArgValues(options::OPT_config);
@@ -1020,7 +1023,18 @@ bool Driver::loadConfigFile() {
         return readConfigFile(CfgFilePath);
       }
 
-      FileSpecifiedExplicitly = true;
+      // Look for the configuration file in the usual locations.
+      if (searchForFile(CfgFilePath, CfgFileSearchDirs, CfgFileName, getVFS()))
+        return readConfigFile(CfgFilePath);
+
+      // Report error but only if config file was specified explicitly, by
+      // option --config. If it was deduced from executable name, it is not an
+      // error.
+      Diag(diag::err_drv_config_file_not_found) << CfgFileName;
+      for (const StringRef &SearchDir : CfgFileSearchDirs)
+        if (!SearchDir.empty())
+          Diag(diag::note_drv_config_file_searched_in) << SearchDir;
+      return true;
     }
   }
 
@@ -1059,8 +1073,8 @@ bool Driver::loadConfigFile() {
     // Get architecture name from config file name like 'i386.cfg' or
     // 'armv7l-clang.cfg'.
     // Check if command line options changes effective triple.
-    llvm::Triple EffectiveTriple = computeTargetTriple(*this,
-                                             CfgTriple.getTriple(), *CLOptions);
+    llvm::Triple EffectiveTriple =
+        computeTargetTriple(*this, CfgTriple.getTriple(), *CLOptions);
     if (CfgTriple.getArch() != EffectiveTriple.getArch()) {
       FixedConfigFile = EffectiveTriple.getArchName();
       FixedArchPrefixLen = FixedConfigFile.size();
@@ -1071,11 +1085,7 @@ bool Driver::loadConfigFile() {
     }
   }
 
-  // Prepare list of directories where config file is searched for.
-  StringRef CfgFileSearchDirs[] = {UserConfigDir, SystemConfigDir, Dir};
-
   // Try to find config file. First try file with corrected architecture.
-  llvm::SmallString<128> CfgFilePath;
   if (!FixedConfigFile.empty()) {
     if (searchForFile(CfgFilePath, CfgFileSearchDirs, FixedConfigFile,
                       getVFS()))
@@ -1101,16 +1111,8 @@ bool Driver::loadConfigFile() {
       return readConfigFile(CfgFilePath);
   }
 
-  // Report error but only if config file was specified explicitly, by option
-  // --config. If it was deduced from executable name, it is not an error.
-  if (FileSpecifiedExplicitly) {
-    Diag(diag::err_drv_config_file_not_found) << CfgFileName;
-    for (const StringRef &SearchDir : CfgFileSearchDirs)
-      if (!SearchDir.empty())
-        Diag(diag::note_drv_config_file_searched_in) << SearchDir;
-    return true;
-  }
-
+  // If we were unable to find a config file deduced from executable name,
+  // do not report an error.
   return false;
 }
 
diff --git a/clang/test/Driver/config-file-errs.c b/clang/test/Driver/config-file-errs.c
index 8db2ea439298c8..c4ce9df915bf30 100644
--- a/clang/test/Driver/config-file-errs.c
+++ b/clang/test/Driver/config-file-errs.c
@@ -24,24 +24,24 @@
 
 //--- Argument of '--config' must exist somewhere in well-known directories, if it is specified by bare name.
 //
-// RUN: not %clang --config-system-dir= --config-user-dir= --config nonexistent-config-file 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND0
+// RUN: not %clang --config-system-dir= --config-user-dir= --config nonexistent-config-file.cfg 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND0
 // CHECK-NOTFOUND0: configuration file 'nonexistent-config-file.cfg' cannot be found
 // CHECK-NOTFOUND0-NEXT: was searched for in the directory:
 // CHECK-NOTFOUND0-NOT: was searched for in the directory:
 //
-// RUN: not %clang --config-system-dir= --config-user-dir=%S/Inputs/config2 --config nonexistent-config-file 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND1
+// RUN: not %clang --config-system-dir= --config-user-dir=%S/Inputs/config2 --config nonexistent-config-file.cfg 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND1
 // CHECK-NOTFOUND1: configuration file 'nonexistent-config-file.cfg' cannot be found
 // CHECK-NOTFOUND1-NEXT: was searched for in the directory: {{.*}}/Inputs/config2
 // CHECK-NOTFOUND1-NEXT: was searched for in the directory:
 // CHECK-NOTFOUND1-NOT: was searched for in the directory:
 //
-// RUN: not %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config nonexistent-config-file 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND2
+// RUN: not %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config nonexistent-config-file.cfg 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND2
 // CHECK-NOTFOUND2: configuration file 'nonexistent-config-file.cfg' cannot be found
 // CHECK-NOTFOUND2-NEXT: was searched for in the directory: {{.*}}/Inputs/config
 // CHECK-NOTFOUND2-NEXT: was searched for in the directory:
 // CHECK-NOTFOUND2-NOT: was searched for in the directory:
 //
-// RUN: not %clang --config-system-dir=%S/Inputs/config --config-user-dir=%S/Inputs/config2 --config nonexistent-config-file 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND3
+// RUN: not %clang --config-system-dir=%S/Inputs/config --config-user-dir=%S/Inputs/config2 --config nonexistent-config-file.cfg 2>&1 | FileCheck %s -check-prefix CHECK-NOTFOUND3
 // CHECK-NOTFOUND3: configuration file 'nonexistent-config-file.cfg' cannot be found
 // CHECK-NOTFOUND3-NEXT: was searched for in the directory: {{.*}}/Inputs/config2
 // CHECK-NOTFOUND3-NEXT: was searched for in the directory: {{.*}}/Inputs/config
diff --git a/clang/test/Driver/config-file.c b/clang/test/Driver/config-file.c
index fde7260ecd73fd..265fd49f2e6642 100644
--- a/clang/test/Driver/config-file.c
+++ b/clang/test/Driver/config-file.c
@@ -68,11 +68,11 @@
 
 //--- User directory is searched first.
 //
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir=%S/Inputs/config2 --config config-4 -S %s -o /dev/null -v 2>&1 | FileCheck %s -check-prefix CHECK-PRECEDENCE
+// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir=%S/Inputs/config2 --config config-4.cfg -S %s -o /dev/null -v 2>&1 | FileCheck %s -check-prefix CHECK-PRECEDENCE
 // CHECK-PRECEDENCE: Configuration file: {{.*}}Inputs{{.}}config2{{.}}config-4.cfg
 // CHECK-PRECEDENCE: -Wall
 
 
 //--- Duplicate --config options are allowed if the value is the same
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir=%S/Inputs/config2 --config config-4 --config config-4 -S %s -o /dev/null -v 2>&1 | FileCheck %s -check-prefix CHECK-SAME-CONFIG
+// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir=%S/Inputs/config2 --config config-4.cfg --config config-4.cfg -S %s -o /dev/null -v 2>&1 | FileCheck %s -check-prefix CHECK-SAME-CONFIG
 // CHECK-SAME-CONFIG: Configuration file: {{.*}}Inputs{{.}}config2{{.}}config-4.cfg
diff --git a/clang/test/Driver/config-file2.c b/clang/test/Driver/config-file2.c
deleted file mode 100644
index 8b57a92e1e83e0..00000000000000
--- a/clang/test/Driver/config-file2.c
+++ /dev/null
@@ -1,51 +0,0 @@
-// REQUIRES: x86-registered-target
-
-//--- Invocation `clang --config x86_64-qqq -m32` loads `i386-qqq.cfg` if the latter exists.
-//
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config x86_64-qqq -m32 -c %s -### 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD
-// CHECK-RELOAD: Target: i386
-// CHECK-RELOAD: Configuration file: {{.*}}Inputs{{.}}config{{.}}i386-qqq.cfg
-
-
-//--- Invocation `clang --config x86_64-qqq2 -m32` loads `i386.cfg` if the latter exists in another search directory.
-//
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir=%S/Inputs/config2 --config x86_64-qqq2 -m32 -c %s -### 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD1
-// CHECK-RELOAD1: Target: i386
-// CHECK-RELOAD1: Configuration file: {{.*}}Inputs{{.}}config2{{.}}i386.cfg
-
-
-//--- Invocation `clang --config x86_64-qqq2 -m32` loads `x86_64-qqq2.cfg` if `i386-qqq2.cfg` and `i386.cfg` do not exist.
-//
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config x86_64-qqq2 -m32 -c %s -### 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD2
-// note: target is overridden due to -m32
-// CHECK-RELOAD2: Target: i386
-// CHECK-RELOAD2: Configuration file: {{.*}}Inputs{{.}}config{{.}}x86_64-qqq2.cfg
-
-
-//--- Invocation `clang --config i386-qqq3 -m64` loads `x86_64.cfg` if `x86_64-qqq3.cfg` does not exist.
-//
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config i386-qqq3 -m64 -c %s -### 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD3
-// CHECK-RELOAD3: Target: x86_64
-// CHECK-RELOAD3: Configuration file: {{.*}}Inputs{{.}}config{{.}}x86_64.cfg
-
-
-//--- Invocation `clang --config x86_64-qqq -target i386` loads `i386-qqq.cfg` if the latter exists.
-//
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config x86_64-qqq -target i386 -c %s -### 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD4
-// CHECK-RELOAD4: Target: i386
-// CHECK-RELOAD4: Configuration file: {{.*}}Inputs{{.}}config{{.}}i386-qqq.cfg
-
-
-//--- Invocation `clang --config x86_64-qqq2 -target i386` loads `x86_64-qqq2.cfg` if `i386-qqq2.cfg` and `i386.cfg` do not exist.
-//
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config x86_64-qqq2 -target i386 -c %s -### 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD5
-// note: target is overridden due to -target i386
-// CHECK-RELOAD5: Target: i386
-// CHECK-RELOAD5: Configuration file: {{.*}}Inputs{{.}}config{{.}}x86_64-qqq2.cfg
-
-
-//--- Invocation `clang --config x86_64-qqq -target i386 -m64` loads `x86_64-qqq.cfg`.
-//
-// RUN: %clang --config-system-dir=%S/Inputs/config --config-user-dir= --config x86_64-qqq -target i386 -m64 -c %s -### 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD6
-// CHECK-RELOAD6: Target: x86_64
-// CHECK-RELOAD6: Configuration file: {{.*}}Inputs{{.}}config{{.}}x86_64-qqq.cfg
diff --git a/clang/test/Driver/config-file3.c b/clang/test/Driver/config-file3.c
index 7fdc2a59133a85..086355b382a1df 100644
--- a/clang/test/Driver/config-file3.c
+++ b/clang/test/Driver/config-file3.c
@@ -37,7 +37,7 @@
 //
 //--- File specified by --config overrides config inferred from clang executable.
 //
-// RUN: %t/testdmode/qqq-clang-g++ --config-system-dir=%S/Inputs/config --config-user-dir= --config i386-qqq -c -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-EXPLICIT
+// RUN: %t/testdmode/qqq-clang-g++ --config-system-dir=%S/Inputs/config --config-user-dir= --config i386-qqq.cfg -c -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-EXPLICIT
 //
 // CHECK-EXPLICIT: Configuration file: {{.*}}/Inputs/config/i386-qqq.cfg
 
@@ -77,27 +77,24 @@
 // RUN: ln -s %clang %t/testreload/x86_64-clang-g++
 // RUN: echo "-Wundefined-func-template" > %t/testreload/i386-clang-g++.cfg
 // RUN: echo "-Werror" > %t/testreload/i386.cfg
+// RUN: echo "-Wall" > %t/testreload/x86_64-clang-g++.cfg
 // RUN: %t/testreload/x86_64-clang-g++ --config-system-dir= --config-user-dir= -c -m32 -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD
 //
 // CHECK-RELOAD: Configuration file: {{.*}}/testreload/i386-clang-g++.cfg
 // CHECK-RELOAD: -Wundefined-func-template
 // CHECK-RELOAD-NOT: -Werror
+// CHECK-RELOAD-NOT: -Wall
 
-//--- If config file is specified by --config and its name does not start with architecture, it is used without reloading.
-//
-// RUN: %t/testreload/x86_64-clang-g++ --config-system-dir=%S/Inputs --config-user-dir= --config config-3 -c -m32 -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD1a
-//
-// CHECK-RELOAD1a: Configuration file: {{.*}}/Inputs/config-3.cfg
-//
-// RUN: %t/testreload/x86_64-clang-g++ --config-system-dir=%S/Inputs --config-user-dir= --config config-3 -c --target=i386 -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD1b
-//
-// CHECK-RELOAD1b: Configuration file: {{.*}}/Inputs/config-3.cfg
+//--- Same for -target in place of -m32.
+// RUN: %t/testreload/x86_64-clang-g++ --config-system-dir= --config-user-dir= -c -target i386 -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD
 
-//--- If config file is specified by --config and its name starts with architecture, it is reloaded.
-//
-// RUN: %t/testreload/x86_64-clang-g++ --config-system-dir=%S/Inputs/config --config-user-dir= --config x86_64-qqq -c -m32 -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD1c
+//--- `-target i386 -m64` should load the 64-bit config.
+// RUN: %t/testreload/x86_64-clang-g++ --config-system-dir= --config-user-dir= -c -target i386 -m64 -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD1a
 //
-// CHECK-RELOAD1c: Configuration file: {{.*}}/Inputs/config/i386-qqq.cfg
+// CHECK-RELOAD1a: Configuration file: {{.*}}/testreload/x86_64-clang-g++.cfg
+// CHECK-RELOAD1a: -Wall
+// CHECK-RELOAD1a-NOT: -Werror
+// CHECK-RELOAD1a-NOT: -Wundefined-func-template
 
 //--- x86_64-clang-g++ tries to find config i386.cfg if i386-clang-g++.cfg is not found.
 //
@@ -107,4 +104,9 @@
 // CHECK-RELOAD1d: Configuration file: {{.*}}/testreload/i386.cfg
 // CHECK-RELOAD1d: -Werror
 // CHECK-RELOAD1d-NOT: -Wundefined-func-template
+// CHECK-RELOAD1d-NOT: -Wall
 
+//--- x86_64-clang-g++ uses x86_64-clang-g++.cfg if i386*.cfg are not found.
+//
+// RUN: rm %t/testreload/i386.cfg
+// RUN: %t/testreload/x86_64-clang-g++ --config-system-dir= --config-user-dir= -c -m32 -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-RELOAD1a