Index: clang/lib/Driver/ToolChains/MinGW.h
===================================================================
--- clang/lib/Driver/ToolChains/MinGW.h
+++ clang/lib/Driver/ToolChains/MinGW.h
@@ -98,6 +98,7 @@
 
   std::string Base;
   std::string GccLibDir;
+  clang::driver::toolchains::Generic_GCC::GCCVersion GccVer;
   std::string Ver;
   std::string Arch;
   mutable std::unique_ptr<tools::gcc::Preprocessor> Preprocessor;
Index: clang/lib/Driver/ToolChains/MinGW.cpp
===================================================================
--- clang/lib/Driver/ToolChains/MinGW.cpp
+++ clang/lib/Driver/ToolChains/MinGW.cpp
@@ -329,8 +329,9 @@
 
 // Simplified from Generic_GCC::GCCInstallationDetector::ScanLibDirForGCCTriple.
 static bool findGccVersion(StringRef LibDir, std::string &GccLibDir,
-                           std::string &Ver) {
-  auto Version = toolchains::Generic_GCC::GCCVersion::Parse("0.0.0");
+                           std::string &Ver,
+                           toolchains::Generic_GCC::GCCVersion &Version) {
+  Version = toolchains::Generic_GCC::GCCVersion::Parse("0.0.0");
   std::error_code EC;
   for (llvm::sys::fs::directory_iterator LI(LibDir, EC), LE; !EC && LI != LE;
        LI = LI.increment(EC)) {
@@ -361,7 +362,7 @@
     for (StringRef CandidateArch : Archs) {
       llvm::SmallString<1024> LibDir(Base);
       llvm::sys::path::append(LibDir, CandidateLib, "gcc", CandidateArch);
-      if (findGccVersion(LibDir, GccLibDir, Ver)) {
+      if (findGccVersion(LibDir, GccLibDir, Ver, GccVer)) {
         Arch = std::string(CandidateArch);
         return;
       }
@@ -424,6 +425,11 @@
   getFilePaths().push_back(GccLibDir);
   getFilePaths().push_back(
       (Base + Arch + llvm::sys::path::get_separator() + "lib").str());
+
+  // Gentoo
+  getFilePaths().push_back(
+      (Base + Arch + llvm::sys::path::get_separator() + "mingw/lib").str());
+
   getFilePaths().push_back(Base + "lib");
   // openSUSE
   getFilePaths().push_back(Base + Arch + "/sys-root/mingw/lib");
@@ -576,6 +582,11 @@
 
   addSystemInclude(DriverArgs, CC1Args,
                    Base + Arch + llvm::sys::path::get_separator() + "include");
+
+  // Gentoo
+  addSystemInclude(DriverArgs, CC1Args,
+                   Base + Arch + llvm::sys::path::get_separator() + "usr/include");
+
   addSystemInclude(DriverArgs, CC1Args, Base + "include");
 }
 
@@ -596,7 +607,7 @@
     break;
 
   case ToolChain::CST_Libstdcxx:
-    llvm::SmallVector<llvm::SmallString<1024>, 4> CppIncludeBases;
+    llvm::SmallVector<llvm::SmallString<1024>, 7> CppIncludeBases;
     CppIncludeBases.emplace_back(Base);
     llvm::sys::path::append(CppIncludeBases[0], Arch, "include", "c++");
     CppIncludeBases.emplace_back(Base);
@@ -605,6 +616,15 @@
     llvm::sys::path::append(CppIncludeBases[2], "include", "c++", Ver);
     CppIncludeBases.emplace_back(GccLibDir);
     llvm::sys::path::append(CppIncludeBases[3], "include", "c++");
+    CppIncludeBases.emplace_back(GccLibDir);
+    llvm::sys::path::append(CppIncludeBases[4], "include",
+                            "g++-v" + GccVer.Text);
+    CppIncludeBases.emplace_back(GccLibDir);
+    llvm::sys::path::append(CppIncludeBases[5], "include",
+                            "g++-v" + GccVer.MajorStr + "." + GccVer.MinorStr);
+    CppIncludeBases.emplace_back(GccLibDir);
+    llvm::sys::path::append(CppIncludeBases[6], "include",
+                            "g++-v" + GccVer.MajorStr);
     for (auto &CppIncludeBase : CppIncludeBases) {
       addSystemInclude(DriverArgs, CC1Args, CppIncludeBase);
       CppIncludeBase += Slash;
Index: clang/test/Driver/mingw-sysroot.cpp
===================================================================
--- clang/test/Driver/mingw-sysroot.cpp
+++ clang/test/Driver/mingw-sysroot.cpp
@@ -21,6 +21,9 @@
 // CHECK_TESTROOT_GCC: "-internal-isystem" "[[BASE:[^"]+]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}c++"
 // CHECK_TESTROOT_GCC-SAME: {{^}} "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}x86_64-w64-mingw32"
 // CHECK_TESTROOT_GCC-SAME: {{^}} "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}backward"
+// CHECK_TESTROOT_GCC: "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}g++-v10.2-posix"
+// CHECK_TESTROOT_GCC: "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}g++-v10.2"
+// CHECK_TESTROOT_GCC: "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}g++-v10"
 // CHECK_TESTROOT_GCC: "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}include"
 
 
Index: clang/test/Driver/mingw.cpp
===================================================================
--- clang/test/Driver/mingw.cpp
+++ clang/test/Driver/mingw.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang -target i686-windows-gnu -rtlib=platform -c -### --sysroot=%S/Inputs/mingw_clang_tree/mingw32 %s 2>&1 | FileCheck -check-prefix=CHECK_MINGW_CLANG_TREE %s
 // CHECK_MINGW_CLANG_TREE: "[[BASE:[^"]+]]/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}include"
+// CHECK_MINGW_CLANG_TREE: "[[BASE:[^"]+]]/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}i686-w64-mingw32{{/|\\\\}}usr{{/|\\\\}}include"
 // CHECK_MINGW_CLANG_TREE: "[[BASE]]/Inputs/mingw_clang_tree/mingw32{{/|\\\\}}include"