diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -69,7 +69,7 @@
   "install, pass a different GPU arch with --cuda-gpu-arch, or pass "
   "--no-cuda-version-check.">;
 def warn_drv_unknown_cuda_version: Warning<
-  "Unknown CUDA version %0. Assuming the latest supported version %1">,
+  "Unknown CUDA version. %0 Assuming the latest supported version %1">,
   InGroup<CudaUnknownVersion>;
 def err_drv_cuda_host_arch : Error<"unsupported architecture '%0' for host compilation.">;
 def err_drv_mix_cuda_hip : Error<"Mixed Cuda and HIP compilation is not supported.">;
diff --git a/clang/lib/Driver/ToolChains/Cuda.h b/clang/lib/Driver/ToolChains/Cuda.h
--- a/clang/lib/Driver/ToolChains/Cuda.h
+++ b/clang/lib/Driver/ToolChains/Cuda.h
@@ -78,9 +78,6 @@
     return LibDeviceMap.lookup(Gpu);
   }
   void WarnIfUnsupportedVersion();
-
-private:
-  void ParseCudaVersionFile(llvm::StringRef V);
 };
 
 namespace tools {
diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -16,6 +16,7 @@
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
@@ -32,29 +33,80 @@
 using namespace clang;
 using namespace llvm::opt;
 
+namespace {
+struct CudaVersionInfo {
+  std::string DetectedVersion;
+  CudaVersion Version;
+};
 // Parses the contents of version.txt in an CUDA installation.  It should
 // contain one line of the from e.g. "CUDA Version 7.5.2".
-void CudaInstallationDetector::ParseCudaVersionFile(llvm::StringRef V) {
-  Version = CudaVersion::UNKNOWN;
+CudaVersionInfo parseCudaVersionFile(llvm::StringRef V) {
+  V = V.trim();
   if (!V.startswith("CUDA Version "))
-    return;
+    return {V.str(), CudaVersion::UNKNOWN};
   V = V.substr(strlen("CUDA Version "));
   SmallVector<StringRef,4> VersionParts;
   V.split(VersionParts, '.');
-  if (VersionParts.size() < 2)
-    return;
-  DetectedVersion = join_items(".", VersionParts[0], VersionParts[1]);
-  Version = CudaStringToVersion(DetectedVersion);
-  if (Version != CudaVersion::UNKNOWN) {
-    // TODO(tra): remove the warning once we have all features of 10.2 and 11.0
-    // implemented.
-    DetectedVersionIsNotSupported = Version > CudaVersion::LATEST_SUPPORTED;
-    return;
+  return {"version.txt: " + V.str() + ".",
+          VersionParts.size() < 2
+              ? CudaVersion::UNKNOWN
+              : CudaStringToVersion(
+                    join_items(".", VersionParts[0], VersionParts[1]))};
+}
+
+CudaVersion getCudaVersion(uint32_t raw_version) {
+  if (raw_version < 7050)
+    return CudaVersion::CUDA_70;
+  if (raw_version < 8000)
+    return CudaVersion::CUDA_75;
+  if (raw_version < 9000)
+    return CudaVersion::CUDA_80;
+  if (raw_version < 9010)
+    return CudaVersion::CUDA_90;
+  if (raw_version < 9020)
+    return CudaVersion::CUDA_91;
+  if (raw_version < 10000)
+    return CudaVersion::CUDA_92;
+  if (raw_version < 10010)
+    return CudaVersion::CUDA_100;
+  if (raw_version < 10020)
+    return CudaVersion::CUDA_101;
+  if (raw_version < 11000)
+    return CudaVersion::CUDA_102;
+  if (raw_version < 11010)
+    return CudaVersion::CUDA_110;
+  return CudaVersion::LATEST;
+}
+
+CudaVersionInfo parseCudaHFile(llvm::StringRef Input) {
+  // Helper lambda which skips the words if the line starts with them or returns
+  // None otherwise.
+  auto StartsWithWords =
+      [](llvm::StringRef Line,
+         const SmallVector<StringRef, 3> words) -> llvm::Optional<StringRef> {
+    for (StringRef word : words) {
+      if (!Line.consume_front(word))
+        return {};
+      Line = Line.ltrim();
+    }
+    return Line;
+  };
+
+  Input = Input.ltrim();
+  while (!Input.empty()) {
+    if (auto Line =
+            StartsWithWords(Input.ltrim(), {"#", "define", "CUDA_VERSION"})) {
+      uint32_t RawVersion;
+      Line->consumeInteger(10, RawVersion);
+      return {"cuda.h: CUDA_VERSION=" + Twine(RawVersion).str() + ".",
+              getCudaVersion(RawVersion)};
+    }
+    // Find next non-empty line.
+    Input = Input.drop_front(Input.find_first_of("\n\r")).ltrim();
   }
-
-  Version = CudaVersion::LATEST_SUPPORTED;
-  DetectedVersionIsNotSupported = true;
+  return {"cuda.h: CUDA_VERSION not found.", CudaVersion::UNKNOWN};
 }
+} // namespace
 
 void CudaInstallationDetector::WarnIfUnsupportedVersion() {
   if (DetectedVersionIsNotSupported)
@@ -152,21 +204,31 @@
     else
       continue;
 
-    llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> VersionFile =
-        FS.getBufferForFile(InstallPath + "/version.txt");
-    if (!VersionFile) {
-      // CUDA 7.0 and CUDA 11.1+ do not have version.txt file.
-      // Use libdevice file to distinguish 7.0 from the new versions.
-      if (FS.exists(LibDevicePath + "/libdevice.10.bc")) {
-        Version = CudaVersion::LATEST;
-        DetectedVersionIsNotSupported = Version > CudaVersion::LATEST_SUPPORTED;
-      } else {
-        Version = CudaVersion::CUDA_70;
-      }
-    } else {
-      ParseCudaVersionFile((*VersionFile)->getBuffer());
+    CudaVersionInfo VersionInfo = {"", CudaVersion::UNKNOWN};
+    if (auto VersionFile = FS.getBufferForFile(InstallPath + "/version.txt"))
+      VersionInfo = parseCudaVersionFile((*VersionFile)->getBuffer());
+    // If version file didn't give us the version, try to find it in cuda.h
+    if (VersionInfo.Version == CudaVersion::UNKNOWN)
+      if (auto CudaHFile = FS.getBufferForFile(InstallPath + "/include/cuda.h"))
+        VersionInfo = parseCudaHFile((*CudaHFile)->getBuffer());
+    // As the last resort, make an educated guess between CUDA-7.0, (which had
+    // no version.txt file and had old-style libdevice bitcode ) and an unknown
+    // recent CUDA version (no version.txt, new style bitcode).
+    if (VersionInfo.Version == CudaVersion::UNKNOWN) {
+      VersionInfo.Version = (FS.exists(LibDevicePath + "/libdevice.10.bc"))
+                                ? Version = CudaVersion::LATEST
+                                : Version = CudaVersion::CUDA_70;
+      VersionInfo.DetectedVersion =
+          "No version found in version.txt or cuda.h.";
     }
 
+    Version = VersionInfo.Version;
+    DetectedVersion = VersionInfo.DetectedVersion;
+
+    // TODO(tra): remove the warning once we have all features of 10.2
+    // and 11.0 implemented.
+    DetectedVersionIsNotSupported = Version > CudaVersion::LATEST_SUPPORTED;
+
     if (Version >= CudaVersion::CUDA_90) {
       // CUDA-9+ uses single libdevice file for all GPU variants.
       std::string FilePath = LibDevicePath + "/libdevice.10.bc";
diff --git a/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/bin/.keep b/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/bin/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/include/.keep b/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/include/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/lib/.keep b/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/lib/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/lib64/.keep b/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/lib64/.keep
new file mode 100644
diff --git a/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/nvvm/libdevice/libdevice.10.bc b/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/nvvm/libdevice/libdevice.10.bc
new file mode 100644
diff --git a/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/version.txt b/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/version.txt
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/Inputs/CUDA_102/usr/local/cuda/version.txt
@@ -0,0 +1 @@
+CUDA Version 10.2.333
diff --git a/clang/test/Driver/Inputs/CUDA_111/usr/local/cuda/include/cuda.h b/clang/test/Driver/Inputs/CUDA_111/usr/local/cuda/include/cuda.h
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/Inputs/CUDA_111/usr/local/cuda/include/cuda.h
@@ -0,0 +1,7 @@
+//
+// Placeholder file for testing CUDA version detection
+//
+
+#define CUDA_VERSION 11010
+
+//
diff --git a/clang/test/Driver/cuda-version-check.cu b/clang/test/Driver/cuda-version-check.cu
--- a/clang/test/Driver/cuda-version-check.cu
+++ b/clang/test/Driver/cuda-version-check.cu
@@ -8,13 +8,15 @@
 // RUN:    FileCheck %s --check-prefix=OK
 // RUN: %clang --target=x86_64-linux -v -### --cuda-gpu-arch=sm_60 --cuda-path=%S/Inputs/CUDA_80/usr/local/cuda 2>&1 %s | \
 // RUN:    FileCheck %s --check-prefix=OK
+// Test version guess when no version.txt or cuda.h are found
 // RUN: %clang --target=x86_64-linux -v -### --cuda-gpu-arch=sm_60 --cuda-path=%S/Inputs/CUDA-unknown/usr/local/cuda 2>&1 %s | \
 // RUN:    FileCheck %s --check-prefix=UNKNOWN_VERSION
-// CUDA versions after 11.0 (update 1) do not carry version.txt file. Make sure
-// we still detect them as a new version and handle them the same as we handle
-// other new CUDA versions.
+// Unknown version with version.txt present
+// RUN: %clang --target=x86_64-linux -v -### --cuda-gpu-arch=sm_60 --cuda-path=%S/Inputs/CUDA_102/usr/local/cuda 2>&1 %s | \
+// RUN:    FileCheck %s --check-prefix=UNKNOWN_VERSION_V
+// Unknown version with no version.txt but with version info present in cuda.h
 // RUN: %clang --target=x86_64-linux -v -### --cuda-gpu-arch=sm_60 --cuda-path=%S/Inputs/CUDA_111/usr/local/cuda 2>&1 %s | \
-// RUN:    FileCheck %s --check-prefix=UNKNOWN_VERSION
+// RUN:    FileCheck %s --check-prefix=UNKNOWN_VERSION_H
 // Make sure that we don't warn about CUDA version during C++ compilation.
 // RUN: %clang --target=x86_64-linux -v -### -x c++ --cuda-gpu-arch=sm_60 \
 // RUN:    --cuda-path=%S/Inputs/CUDA-unknown/usr/local/cuda 2>&1 %s | \
@@ -70,5 +72,7 @@
 // ERR_SM61: error: GPU arch sm_61 {{.*}}
 // ERR_SM61-NOT: error: GPU arch sm_61
 
-// UNKNOWN_VERSION: Unknown CUDA version {{.*}}. Assuming the latest supported version
+// UNKNOWN_VERSION_V: Unknown CUDA version. version.txt:{{.*}}. Assuming the latest supported version
+// UNKNOWN_VERSION_H: Unknown CUDA version. cuda.h: CUDA_VERSION={{.*}}. Assuming the latest supported version
+// UNKNOWN_VERSION: Unknown CUDA version. No version found in version.txt or cuda.h. Assuming the latest supported version
 // UNKNOWN_VERSION_CXX-NOT: Unknown CUDA version