[llvm-cov] Improve error message for missing profdata

[efriedma]

Summary

I got a report recently that a user was having trouble interpreting the meaning of the error message. Hopefully this is more readable; produces something like the following:

error: No such file or directory: Could not read profile data.

[davidxl]

llvm/tools/llvm-cov/CodeCoverage.cpp

871

a nit : all the other messages uses '!' at the end, so keep it consistent here?

[vsk]

Thanks, lgtm. I don't have a strong opinion on the message format -- David's suggestion sounds reasonable.

llvm/test/tools/llvm-cov/misssing-profdata.test

+RUN: not llvm-cov show -instr-profile=%t.nonexistent %t.nonexistent 2>&1 | FileCheck %s
+CHECK: Could not read profile data

llvm/tools/llvm-cov/CodeCoverage.cpp

int CodeCoverageTool::doShow(int argc, const char **argv,
   if (ViewOpts.hasOutputDirectory()) {
     if (auto E = sys::fs::create_directories(ViewOpts.ShowOutputDirectory)) {
       error("Could not create output directory!", E.message());
       return 1;
     }
   }
 
   sys::fs::file_status Status;
-  if (sys::fs::status(PGOFilename, Status)) {
-    error("profdata file error: can not get the file status. \n");
+  if (std::error_code EC = sys::fs::status(PGOFilename, Status)) {
+    error("Could not read profile data.", EC.message());
     return 1;
   }
 
   auto ModifiedTime = Status.getLastModificationTime();
   std::string ModifiedTimeStr = to_string(ModifiedTime);
   size_t found = ModifiedTimeStr.rfind(':');
   ViewOpts.CreatedTimeStr = (found != std::string::npos)
                                 ? "Created: " + ModifiedTimeStr.substr(0, found)