bugpoint: add flag -verbose-errors

[sebpop]

Summary

The default behavior of bugpoint is to print "<crash>" when it finds a reduced test that crashes compilation.
With this flag we now can see the output of the crashing program.
This is useful to make sure it is the same error being tracked down and not a different error that happens to crash the compiler as well.

[silvas]

I've been using bugpoint quite a bit recently and this seems handy!

This LGTM with an update to http://llvm.org/docs/CommandGuide/bugpoint.html (docs/CommandGuide/bugpoint.rst)

[sebpop]

Added documentation. If there are no other comments I will push the change later today.

llvm/trunk/docs/CommandGuide/bugpoint.rst

  will be the minimum bitcode that passes FileCheck.
 
 **--safe-path** *path*
 
  This option defines the path to the command to execute with the
  **--safe-{int,jit,llc,custom}**
  option.
 
+**--verbose-errors**\ =\ *{true,false}*
+
+ The default behavior of bugpoint is to print "<crash>" when it finds a reduced
+ test that crashes compilation. This flag prints the output of the crashing
+ program to stderr. This is useful to make sure it is the same error being
+ tracked down and not a different error that happens to crash the compiler as
+ well. Defaults to false.
+
 EXIT STATUS
 -----------
 
 If **bugpoint** succeeds in finding a problem, it will exit with 0.  Otherwise,
 if an error occurs, it will exit with a non-zero value.
 
 SEE ALSO
 --------
 
 opt|opt

llvm/trunk/tools/bugpoint/CrashDebugger.cpp

namespace {
   cl::opt<bool>
   DontReducePassList("disable-pass-list-reduction",
                      cl::desc("Skip pass list reduction steps"),
                      cl::init(false));
 
   cl::opt<bool> NoNamedMDRM("disable-namedmd-remove",
                             cl::desc("Do not remove global named metadata"),
                             cl::init(false));
+  cl::opt<bool> VerboseErrors("verbose-errors",
+                            cl::desc("Print the output of crashing program"),
+                            cl::init(false));
 }
 
 namespace llvm {
   class ReducePassList : public ListReducer<std::string> {
     BugDriver &BD;
   public:
     ReducePassList(BugDriver &bd) : BD(bd) {}
 
bool BugDriver::debugOptimizerCrash(const std::string &ID) {
   assert(Error.empty());
   return Success;
 }
 
 static bool TestForCodeGenCrash(const BugDriver &BD, Module *M) {
   std::string Error;
   BD.compileProgram(M, &Error);
   if (!Error.empty()) {
+    if (VerboseErrors)
+      errs() << Error << "\n";
+    else
       errs() << "<crash>\n";
     return true;  // Tool is still crashing.
   }
   errs() << '\n';
   return false;
 }
 
 /// debugCodeGeneratorCrash - This method is called when the code generator
 /// crashes on an input.  It attempts to reduce the input as much as possible
 /// while still causing the code generator to crash.
 bool BugDriver::debugCodeGeneratorCrash(std::string &Error) {
   errs() << "*** Debugging code generator crash!\n";
 
   return DebugACrash(*this, TestForCodeGenCrash, Error);
 }