[ELF][Driver] Produce a proper error when file is not found

When a file is not found, produce a proper error message. The previous error
message produced a file format error, which made me wonder for a while why
there is a file format error, but essentially the file was not found.

This fixes the problem by producing a proper error message.

llvm-svn: 217359

lld/lib/Driver/GnuLdDriver.cpp

@@ -488,6 +488,10 @@ bool GnuLdDriver::parse(int argc, const char *argv[],
       // FIXME: Calling getFileMagic() is expensive.  It would be better to
       // wire up the LdScript parser into the registry.
       llvm::sys::fs::file_magic magic = llvm::sys::fs::file_magic::unknown;
+      if (!llvm::sys::fs::exists(resolvedInputPath)) {
+        diagnostics << "lld: cannot find file " << userPath << "\n";
+        return false;
+      }
       std::error_code ec = getFileMagic(*ctx, resolvedInputPath, magic);
       if (ec) {
         diagnostics << "lld: unknown input file format for file " << userPath

lld/test/elf/filenotfound.test

@@ -0,0 +1,3 @@
+# Check that a file that cannot be found results in a proper error message
+RUN: not lld -flavor gnu -target x86_64 %p/Inputs/nofile.o 2>&1 | FileCheck %s
+#CHECK: lld: cannot find file {{[-_A-Za-z0-9.\\/:]+}}nofile.o