Added some helpful logging to "as"

Author: Dan Liew

driver/as

@@ -32,6 +32,7 @@ argFilter = BCFilter(sys.argv[1:])
 try:
     [infile] = argFilter.inputFiles
 except ValueError:
+    logging.debug('Input file argument not detected, assuming stdin.')
     infile = "-"
 
 # set llvm-as
@@ -41,14 +42,20 @@ if os.getenv(llvmCompilerPathEnv):
 
 # Now compile this llvm assembly file into a bitcode file.  The output
 # filename is the same as the object with a .bc appended
-(dirs, filename) = os.path.split(argFilter.outFileName)
+try:
+    (dirs, filename) = os.path.split(argFilter.outFileName)
+except AttributeError as e:
+    logging.error('Output file argument not found.\nException message: ' + str(e))
+    sys.exit(1)
+
 bcfilename = '.{0}.bc'.format(filename)
 bcPath = os.path.join(dirs, bcfilename)
 fakeAssembler = [llvmAssembler, infile, '-o', bcPath]
 asmProc = Popen(fakeAssembler)
 realRet = asmProc.wait()
 
 if realRet != 0:
+    logging.error('llvm-as failed')
     sys.exit(realRet)
 
 attachBitcodePathToObject(bcPath, argFilter.outFileName)