Driver: fix an assertion with `-print-prog-name=`

Fix an assertion when -print-prog-name= is invoked without parameter.
Returns an empty string.

Patch by Christian Bruel!

llvm-svn: 331296

clang/lib/Driver/Driver.cpp

@@ -1594,7 +1594,13 @@ bool Driver::HandleImmediateArgs(const Compilation &C) {
   }
 
   if (Arg *A = C.getArgs().getLastArg(options::OPT_print_prog_name_EQ)) {
-    llvm::outs() << GetProgramPath(A->getValue(), TC) << "\n";
+    StringRef ProgName = A->getValue();
+
+    // Null program name cannot have a path.
+    if (! ProgName.empty())
+      llvm::outs() << GetProgramPath(ProgName, TC);
+
+    llvm::outs() << "\n";
     return false;
   }
 

clang/test/Driver/print-empty-prog-name.c

@@ -0,0 +1,5 @@
+// Test that -print-prog-name= correctly returns an empty string
+
+// RUN: %clang -print-prog-name= 2>&1 | FileCheck %s
+// CHECK-NOT:{{.+}}
+