Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -1058,73 +1058,75 @@
 bool Driver::loadDefaultConfigFiles(ArrayRef<StringRef> CfgFileSearchDirs) {
   if (CLOptions && CLOptions->hasArg(options::OPT_no_default_config))
     return false;
-  if (ClangNameParts.TargetPrefix.empty())
-    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'.
-  std::string CfgFileName =
-        ClangNameParts.TargetPrefix + '-' + ClangNameParts.ModeSuffix;
-
-  // Determine architecture part of the file name, if it is present.
-  StringRef CfgFileArch = CfgFileName;
-  size_t ArchPrefixLen = CfgFileArch.find('-');
-  if (ArchPrefixLen == StringRef::npos)
-    ArchPrefixLen = CfgFileArch.size();
-  llvm::Triple CfgTriple;
-  CfgFileArch = CfgFileArch.take_front(ArchPrefixLen);
-  CfgTriple = llvm::Triple(llvm::Triple::normalize(CfgFileArch));
-  if (CfgTriple.getArch() == llvm::Triple::ArchType::UnknownArch)
-    ArchPrefixLen = 0;
-
-  if (!StringRef(CfgFileName).endswith(".cfg"))
-    CfgFileName += ".cfg";
-
-  // If config file starts with architecture name and command line options
-  // redefine architecture (with options like -m32 -LE etc), try finding new
-  // config file with that architecture.
-  SmallString<128> FixedConfigFile;
-  size_t FixedArchPrefixLen = 0;
-  if (ArchPrefixLen) {
-    // 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);
-    if (CfgTriple.getArch() != EffectiveTriple.getArch()) {
-      FixedConfigFile = EffectiveTriple.getArchName();
-      FixedArchPrefixLen = FixedConfigFile.size();
-      // Append the rest of original file name so that file name transforms
-      // like: i386-clang.cfg -> x86_64-clang.cfg.
-      if (ArchPrefixLen < CfgFileName.size())
-        FixedConfigFile += CfgFileName.substr(ArchPrefixLen);
-    }
-  }
-
-  // Try to find config file. First try file with corrected architecture.
+  // from executable name.
+
+  StringRef EffectiveDriverMode;
+  if (CLOptions)
+    EffectiveDriverMode = CLOptions->getLastArgValue(options::OPT_driver_mode);
+  if (EffectiveDriverMode.empty())
+    EffectiveDriverMode = ClangNameParts.DriverMode;
+
+  llvm::Triple EffectiveTriple =
+      computeTargetTriple(*this, TargetTriple, *CLOptions);
+  assert(!EffectiveTriple.str().empty());
+  StringRef EffectiveModeSuffix = llvm::StringSwitch<const char *>(EffectiveDriverMode)
+                   .Case("g++", "clang++")
+                   .Case("cpp", "clang-cpp")
+                   .Case("cl", "clang-cl")
+                   .Case("flang", "flang")
+                   .Case("dxc", "clang-dxc")
+                   .Default("clang");
+
+  // Start with the effective triple and driver mode since this should yield the most correct config for our invocation.
   llvm::SmallString<128> CfgFilePath;
-  if (!FixedConfigFile.empty()) {
-    if (searchForFile(CfgFilePath, CfgFileSearchDirs, FixedConfigFile,
-                      getVFS()))
-      return readConfigFile(CfgFilePath);
-    // If 'x86_64-clang.cfg' was not found, try 'x86_64.cfg'.
-    FixedConfigFile.resize(FixedArchPrefixLen);
-    FixedConfigFile.append(".cfg");
-    if (searchForFile(CfgFilePath, CfgFileSearchDirs, FixedConfigFile,
-                      getVFS()))
-      return readConfigFile(CfgFilePath);
-  }
-
-  // Then try original file name.
+  std::string CfgFileName = EffectiveTriple.str() + '-' + EffectiveModeSuffix.str() + ".cfg";
   if (searchForFile(CfgFilePath, CfgFileSearchDirs, CfgFileName, getVFS()))
     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);
-    CfgFileName.append(".cfg");
+  // If we can deduce prefix and suffix from the filename, try it next.
+  std::string FixedTargetPrefix;
+  if (!ClangNameParts.TargetPrefix.empty()) {
+    // Determine architecture part of the file name. If it is different
+    // from the effective target, replace the architecture in the filename
+    // prefix.
+    StringRef ArchPrefix, PostArchPart;
+    std::tie(ArchPrefix, PostArchPart) = llvm::StringRef(ClangNameParts.TargetPrefix).split('-');
+    llvm::Triple ArchTriple{llvm::Triple::normalize(ArchPrefix)};
+    if (ArchTriple.getArch() != llvm::Triple::ArchType::UnknownArch && ArchTriple.getArch() != EffectiveTriple.getArch()) {
+      FixedTargetPrefix = EffectiveTriple.getArchName().str() + '-' + PostArchPart.str();
+
+      // Try finding a config file with the corrected architecture,
+      // e.g. "x86_64-clang.cfg" -> "i386-clang.cfg".
+      CfgFileName = FixedTargetPrefix + '-' + ClangNameParts.ModeSuffix
+        + ".cfg";
+      if (searchForFile(CfgFilePath, CfgFileSearchDirs, CfgFileName, getVFS()))
+        return readConfigFile(CfgFilePath);
+    }
+
+    // Then try the original file name.
+    CfgFileName = ClangNameParts.TargetPrefix + '-' + ClangNameParts.ModeSuffix
+      + ".cfg";
+    if (searchForFile(CfgFilePath, CfgFileSearchDirs, CfgFileName, getVFS()))
+      return readConfigFile(CfgFilePath);
+  }
+
+  // If we haven't been successful with the full name, try finding separate configs for target and for driver, and loading both.
+  for (auto &Triple : {EffectiveTriple.str(), FixedTargetPrefix, ClangNameParts.TargetPrefix}) {
+    if (Triple.empty())
+      continue;
+    CfgFileName = Triple + ".cfg";
+    if (searchForFile(CfgFilePath, CfgFileSearchDirs, CfgFileName, getVFS())) {
+      if (readConfigFile(CfgFilePath))
+        return true;
+      break;
+    }
+  }
+  for (auto &ModeName : {EffectiveModeSuffix.str(), ClangNameParts.ModeSuffix}) {
+    if (ModeName.empty())
+      continue;
+    CfgFileName = ModeName + ".cfg";
     if (searchForFile(CfgFilePath, CfgFileSearchDirs, CfgFileName, getVFS()))
       return readConfigFile(CfgFilePath);
   }