Introduce OMPSS2_RUNTIME env var to select the OmpSs-2 runtime. See more

The priority comparing it with clang cmake option and -fompss-2= option
is as follows

(more priority) -fompss-2=  > OMPSS2_RUNTIME > CLANG_DEFAULT_OMPSS2_RUNTIME (less priority)

Closes llvm#184

Author: Raúl Peñacoba Veigas

clang/lib/Driver/Driver.cpp

@@ -777,6 +777,11 @@ Driver::OpenMPRuntimeKind Driver::getOpenMPRuntime(const ArgList &Args) const {
 Driver::OmpSsRuntimeKind Driver::getOmpSsRuntime(const ArgList &Args) const {
   StringRef RuntimeName(CLANG_DEFAULT_OMPSS2_RUNTIME);
 
+  std::optional<std::string> OMPSS2Runtime =
+      llvm::sys::Process::GetEnv("OMPSS2_RUNTIME");
+  if (OMPSS2Runtime && !OMPSS2Runtime->empty())
+    RuntimeName = OMPSS2Runtime.value();
+
   const Arg *A = Args.getLastArg(options::OPT_fompss_EQ);
   if (A)
     RuntimeName = A->getValue();
@@ -790,6 +795,9 @@ Driver::OmpSsRuntimeKind Driver::getOmpSsRuntime(const ArgList &Args) const {
     if (A)
       Diag(diag::err_drv_unsupported_option_argument)
           << A->getSpelling() << A->getValue();
+    else if (OMPSS2Runtime && !OMPSS2Runtime->empty())
+      Diag(diag::err_drv_unsupported_option_argument)
+          << "-fompss-2=" << OMPSS2Runtime.value();
     else
       // FIXME: We could use a nicer diagnostic here.
       Diag(diag::err_drv_unsupported_opt) << "-fompss-2";

clang/test/OmpSs/Driver/runtime.c

@@ -16,3 +16,25 @@
 // CHECK2: clang: error: unsupported argument 'libasdf' to option '-fompss-2='
 // CHECK3: clang: error: unsupported argument 'libasdf' to option '-fompss-2='
 // CHECK3: clang: error: unsupported argument 'libasdf' to option '-fompss-2='
+
+// OMPSS2_RUNTIME priority check
+
+// CompileJob
+// RUN: OMPSS2_RUNTIME=libkaka %clang -fompss-2 %s -c -### 2>&1 | FileCheck %s --check-prefix=CHECK4
+// RUN: OMPSS2_RUNTIME=libkaka %clang -fompss-2=libasdf %s -c -### 2>&1 | FileCheck %s --check-prefix=CHECK5
+// LinkJob
+// RUN: touch %t.o
+// RUN: OMPSS2_RUNTIME=libkaka %clang -fompss-2 %t.o -### 2>&1 | FileCheck %s --check-prefix=CHECK6
+// RUN: OMPSS2_RUNTIME=libkaka %clang -fompss-2=libasdf %t.o -### 2>&1 | FileCheck %s --check-prefix=CHECK7
+// CompileAndLinkJob
+// RUN: OMPSS2_RUNTIME=libkaka %clang -fompss-2 %s -### 2>&1 | FileCheck %s --check-prefix=CHECK8
+// RUN: OMPSS2_RUNTIME=libkaka %clang -fompss-2=libasdf %s -### 2>&1 | FileCheck %s --check-prefix=CHECK9
+
+// CHECK4: clang: error: unsupported argument 'libkaka' to option '-fompss-2='
+// CHECK5: clang: error: unsupported argument 'libasdf' to option '-fompss-2='
+// CHECK6: clang: error: unsupported argument 'libkaka' to option '-fompss-2='
+// CHECK7: clang: error: unsupported argument 'libasdf' to option '-fompss-2='
+// CHECK8: clang: error: unsupported argument 'libkaka' to option '-fompss-2='
+// CHECK8: clang: error: unsupported argument 'libkaka' to option '-fompss-2='
+// CHECK9: clang: error: unsupported argument 'libasdf' to option '-fompss-2='
+// CHECK9: clang: error: unsupported argument 'libasdf' to option '-fompss-2='