commit eb2ba2ea953b5ea73cdbb598f77470bde1c6a011
Author: Artem Belevich <tra@google.com>
Date:   Wed Mar 11 14:53:03 2020 -0700

    [CUDA] Warn about unsupported CUDA SDK version only if it's used.
    
    This fixes an issue with clang issuing a warning about unknown CUDA SDK if it's
    detected during non-CUDA compilation.
    
    Differential Revision: https://reviews.llvm.org/D76030

diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
index 01c5a9175da..78139add8a8 100644
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -34,24 +34,28 @@ using namespace llvm::opt;
 
 // 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".
-static CudaVersion ParseCudaVersionFile(const Driver &D, llvm::StringRef V) {
+void CudaInstallationDetector::ParseCudaVersionFile(llvm::StringRef V) {
+  Version = CudaVersion::UNKNOWN;
   if (!V.startswith("CUDA Version "))
-    return CudaVersion::UNKNOWN;
+    return;
   V = V.substr(strlen("CUDA Version "));
   SmallVector<StringRef,4> VersionParts;
   V.split(VersionParts, '.');
   if (VersionParts.size() < 2)
-    return CudaVersion::UNKNOWN;
-  std::string MajorMinor = join_items(".", VersionParts[0], VersionParts[1]);
-  CudaVersion Version = CudaStringToVersion(MajorMinor);
+    return;
+  DetectedVersion = join_items(".", VersionParts[0], VersionParts[1]);
+  Version = CudaStringToVersion(DetectedVersion);
   if (Version != CudaVersion::UNKNOWN)
-    return Version;
+    return;
 
-  // Issue a warning and assume that the version we've found is compatible with
-  // the latest version we support.
-  D.Diag(diag::warn_drv_unknown_cuda_version)
-      << MajorMinor << CudaVersionToString(CudaVersion::LATEST);
-  return CudaVersion::LATEST;
+  Version = CudaVersion::LATEST;
+  DetectedVersionIsNotSupported = true;
+}
+
+void CudaInstallationDetector::WarnIfUnsupportedVersion() {
+  if (DetectedVersionIsNotSupported)
+    D.Diag(diag::warn_drv_unknown_cuda_version)
+        << DetectedVersion << CudaVersionToString(Version);
 }
 
 CudaInstallationDetector::CudaInstallationDetector(
@@ -150,7 +154,7 @@ CudaInstallationDetector::CudaInstallationDetector(
       // version.txt isn't present.
       Version = CudaVersion::CUDA_70;
     } else {
-      Version = ParseCudaVersionFile(D, (*VersionFile)->getBuffer());
+      ParseCudaVersionFile((*VersionFile)->getBuffer());
     }
 
     if (Version >= CudaVersion::CUDA_90) {
@@ -568,8 +572,10 @@ CudaToolChain::CudaToolChain(const Driver &D, const llvm::Triple &Triple,
                              const Action::OffloadKind OK)
     : ToolChain(D, Triple, Args), HostTC(HostTC),
       CudaInstallation(D, HostTC.getTriple(), Args), OK(OK) {
-  if (CudaInstallation.isValid())
+  if (CudaInstallation.isValid()) {
+    CudaInstallation.WarnIfUnsupportedVersion();
     getProgramPaths().push_back(std::string(CudaInstallation.getBinPath()));
+  }
   // Lookup binaries into the driver directory, this is used to
   // discover the clang-offload-bundler executable.
   getProgramPaths().push_back(getDriver().Dir);
diff --git a/clang/lib/Driver/ToolChains/Cuda.h b/clang/lib/Driver/ToolChains/Cuda.h
index 72ffda83e55..3de98c11a21 100644
--- a/clang/lib/Driver/ToolChains/Cuda.h
+++ b/clang/lib/Driver/ToolChains/Cuda.h
@@ -30,6 +30,8 @@ private:
   const Driver &D;
   bool IsValid = false;
   CudaVersion Version = CudaVersion::UNKNOWN;
+  std::string DetectedVersion;
+  bool DetectedVersionIsNotSupported = false;
   std::string InstallPath;
   std::string BinPath;
   std::string LibPath;
@@ -75,6 +77,10 @@ public:
   std::string getLibDeviceFile(StringRef Gpu) const {
     return LibDeviceMap.lookup(Gpu);
   }
+  void WarnIfUnsupportedVersion();
+
+private:
+  void ParseCudaVersionFile(llvm::StringRef V);
 };
 
 namespace tools {
diff --git a/clang/test/Driver/cuda-version-check.cu b/clang/test/Driver/cuda-version-check.cu
index 5654d4cb7f7..a09b248304f 100644
--- a/clang/test/Driver/cuda-version-check.cu
+++ b/clang/test/Driver/cuda-version-check.cu
@@ -10,6 +10,10 @@
 // RUN:    FileCheck %s --check-prefix=OK
 // 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
+// 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 | \
+// RUN:    FileCheck %s --check-prefix=UNKNOWN_VERSION_CXX
 
 // The installation at Inputs/CUDA is CUDA 7.0, which doesn't support sm_60.
 // RUN: %clang --target=x86_64-linux -v -### --cuda-gpu-arch=sm_60 --cuda-path=%S/Inputs/CUDA/usr/local/cuda 2>&1 %s | \
@@ -62,3 +66,4 @@
 // ERR_SM61-NOT: error: GPU arch sm_61
 
 // UNKNOWN_VERSION: Unknown CUDA version 999.999. Assuming the latest supported version
+// UNKNOWN_VERSION_CXX-NOT: Unknown CUDA version