Index: lib/Driver/ToolChains/MSVC.h
===================================================================
--- lib/Driver/ToolChains/MSVC.h
+++ lib/Driver/ToolChains/MSVC.h
@@ -14,6 +14,7 @@
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Tool.h"
 #include "clang/Driver/ToolChain.h"
+#include "llvm/ADT/SmallString.h"
 
 namespace clang {
 namespace driver {
@@ -128,10 +129,14 @@
 
   Tool *buildLinker() const override;
   Tool *buildAssembler() const override;
+  bool findVCToolChainViaEnvironment(std::string &Path,
+                                     bool &IsVS2017OrNewer);
 private:
   std::string VCToolChainPath;
   bool IsVS2017OrNewer = false;
   CudaInstallationDetector CudaInstallation;
+  llvm::SmallString<128> linkPath;
+  mutable VersionTuple MSVT;
 };
 
 } // end namespace toolchains
Index: lib/Driver/ToolChains/MSVC.cpp
===================================================================
--- lib/Driver/ToolChains/MSVC.cpp
+++ lib/Driver/ToolChains/MSVC.cpp
@@ -69,14 +69,15 @@
 using namespace clang;
 using namespace llvm::opt;
 
+static VersionTuple getMSVCVersionFromExe(const std::string &BinDir);
 // Defined below.
 // Forward declare this so there aren't too many things above the constructor.
 static bool getSystemRegistryString(const char *keyPath, const char *valueName,
                                     std::string &value, std::string *phValue);
 
 // Check various environment variables to try and find a toolchain.
-static bool findVCToolChainViaEnvironment(std::string &Path,
-                                          bool &IsVS2017OrNewer) {
+bool MSVCToolChain::findVCToolChainViaEnvironment(std::string &Path,
+                                                  bool &IsVS2017OrNewer) {
   // These variables are typically set by vcvarsall.bat
   // when launching a developer command prompt.
   if (llvm::Optional<std::string> VCToolsInstallDir =
@@ -117,6 +118,10 @@
       if (!llvm::sys::fs::exists(ExeTestPath))
         continue;
 
+      MSVT = getMSVCVersionFromExe(PathEntry);
+      if (MSVT.empty())
+        continue;
+
       // cl.exe existing isn't a conclusive test for a VC toolchain; clang also
       // has a cl.exe. So let's check for link.exe too.
       ExeTestPath = PathEntry;
@@ -124,53 +129,24 @@
       if (!llvm::sys::fs::exists(ExeTestPath))
         continue;
 
-      // whatever/VC/bin --> old toolchain, VC dir is toolchain dir.
-      llvm::StringRef TestPath = PathEntry;
-      bool IsBin = llvm::sys::path::filename(TestPath).equals_lower("bin");
-      if (!IsBin) {
-        // Strip any architecture subdir like "amd64".
+      // The install directory will be the parent of the include directory,
+      // which must be an higher up in the path from cl.exe.
+      llvm::SmallString<256> TestPath = PathEntry;
+      while(!TestPath.empty()) {
         TestPath = llvm::sys::path::parent_path(TestPath);
-        IsBin = llvm::sys::path::filename(TestPath).equals_lower("bin");
-      }
-      if (IsBin) {
-        llvm::StringRef ParentPath = llvm::sys::path::parent_path(TestPath);
-        if (llvm::sys::path::filename(ParentPath) == "VC") {
-          Path = ParentPath;
-          IsVS2017OrNewer = false;
-          return true;
-        }
-
-      } else {
-        // This could be a new (>=VS2017) toolchain. If it is, we should find
-        // path components with these prefixes when walking backwards through
-        // the path.
-        // Note: empty strings match anything.
-        llvm::StringRef ExpectedPrefixes[] = {"",     "Host",  "bin", "",
-                                              "MSVC", "Tools", "VC"};
-
-        auto It = llvm::sys::path::rbegin(PathEntry);
-        auto End = llvm::sys::path::rend(PathEntry);
-        for (llvm::StringRef Prefix : ExpectedPrefixes) {
-          if (It == End)
-            goto NotAToolChain;
-          if (!It->startswith(Prefix))
-            goto NotAToolChain;
-          ++It;
+        llvm::sys::path::append(TestPath, "include");
+        if (llvm::sys::fs::exists(TestPath)) {
+          Path = llvm::sys::path::parent_path(TestPath);
+          break;
         }
-
-        // We've found a new toolchain!
-        // Back up 3 times (/bin/Host/arch) to get the root path.
-        llvm::StringRef ToolChainPath(PathEntry);
-        for (int i = 0; i < 3; ++i)
-          ToolChainPath = llvm::sys::path::parent_path(ToolChainPath);
-
-        Path = ToolChainPath;
-        IsVS2017OrNewer = true;
-        return true;
       }
 
-    NotAToolChain:
-      continue;
+      if (Path.empty())
+        return false;
+
+      linkPath = ExeTestPath;
+      IsVS2017OrNewer = (MSVT.getMajor() >= 19 && MSVT.getMinor());
+      return true;
     }
   }
   return false;
@@ -467,7 +443,8 @@
     // If we're using the MSVC linker, it's not sufficient to just use link
     // from the program PATH, because other environments like GnuWin32 install
     // their own link.exe which may come first.
-    linkPath = FindVisualStudioExecutable(TC, "link.exe");
+    if (linkPath.empty())
+      linkPath = FindVisualStudioExecutable(TC, "link.exe");
 
 #ifdef USE_WIN32
     // When cross-compiling with VS2017 or newer, link.exe expects to have
@@ -1241,7 +1218,8 @@
                                            types::ID InputType) const {
   // The MSVC version doesn't care about the architecture, even though it
   // may look at the triple internally.
-  VersionTuple MSVT = computeMSVCVersion(/*D=*/nullptr, Args);
+  if (MSVT.empty())
+    MSVT = computeMSVCVersion(/*D=*/nullptr, Args);
   MSVT = VersionTuple(MSVT.getMajor(), MSVT.getMinor().getValueOr(0),
                       MSVT.getSubminor().getValueOr(0));