Fix check-llvm on kernel 4.9+ with asan or msan

[vitalybuka]

Summary

Before https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=v4.9.46&id=84638335900f1995495838fe1bd4870c43ec1f67
test worked because memory allocated with mmap was not counted against RLIMIT_DATA.

[vitalybuka]

Update doc string

[eugenis]

LGTM with TSan

tools/bugpoint/bugpoint.cpp

172

what about TSan?

[vitalybuka]

Added tsan

tools/bugpoint/bugpoint.cpp

static cl::list<std::string>
     InputFilenames(cl::Positional, cl::OneOrMore,
                    cl::desc("<input llvm ll/bc files>"));
 
 static cl::opt<unsigned> TimeoutValue(
     "timeout", cl::init(300), cl::value_desc("seconds"),
     cl::desc("Number of seconds program is allowed to run before it "
              "is killed (default is 300s), 0 disables timeout"));
 
-static cl::opt<int>
-    MemoryLimit("mlimit", cl::init(-1), cl::value_desc("MBytes"),
-                cl::desc("Maximum amount of memory to use. 0 disables check."
-                         " Defaults to 400MB (800MB under valgrind)."));
+static cl::opt<int> MemoryLimit(
+    "mlimit", cl::init(-1), cl::value_desc("MBytes"),
+    cl::desc("Maximum amount of memory to use. 0 disables check. Defaults to "
+             "400MB (800MB under valgrind, 0 with sanitizers)."));
 
 static cl::opt<bool>
     UseValgrind("enable-valgrind",
                 cl::desc("Run optimizations through valgrind"));
 
 // The AnalysesList is automatically populated with registered Passes by the
 // PassNameParser.
 //
#endif
 
   if (MemoryLimit < 0) {
     // Set the default MemoryLimit.  Be sure to update the flag's description if
     // you change this.
     if (sys::RunningOnValgrind() || UseValgrind)
       MemoryLimit = 800;
     else
       MemoryLimit = 400;
+#if LLVM_ADDRESS_SANITIZER_BUILD || LLVM_MEMORY_SANITIZER_BUILD
+    // Starting from kernel 4.9 memory allocated with mmap is counted against
+    // RLIMIT_DATA. Sanitizers need to allocate tens of terabytes for shadow.
+    MemoryLimit = 0;
+#endif
   }
 
   BugDriver D(argv[0], FindBugs, TimeoutValue, MemoryLimit, UseValgrind,
               Context);
   if (D.addSources(InputFilenames))
     return 1;
 
   AddToDriver PM(D);