Fix for test_bitwise subtests for ROCm. (#16)

The issue was that the kernel names were colliding with each other in
the cache.  Since the kernel names were based on the date and time, the
kernels were getting compiled so fast that a subsequent kernel would end
up with the same name as the previous one and would therefore overwrite
it in the cache.

It seems to run the same test multiple times but the subsequent runs
would end up using the wrong kernel because of the collisions.

It is fixed by appending a randomly generated alphanumeric string to
keep the kernel names unique.

lib/driver/llvm.cc

@@ -26,6 +26,7 @@
 #include <memory>
 #include <regex>
 #include <iomanip>
+#include <string>
 #include "triton/driver/llvm.h"
 #include "triton/driver/dispatch.h"
 #include "triton/driver/error.h"
@@ -70,6 +71,24 @@ extern "C"
   int setupterm(char *term, int fildes, int *errret) { return 0; }
 }
 
+namespace {
+
+std::string gen_random(const int len) {
+    static const char alphanum[] =
+        "0123456789"
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+        "abcdefghijklmnopqrstuvwxyz";
+    std::string tmp_s;
+    tmp_s.reserve(len);
+
+    for (int i = 0; i < len; ++i) {
+        tmp_s += alphanum[rand() % (sizeof(alphanum) - 1)];
+    }
+    return tmp_s;
+}
+
+}
+
 namespace triton
 {
   namespace driver
@@ -286,7 +305,7 @@ namespace triton
       auto in_time_t = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
       std::stringstream cur_time;
       cur_time << std::put_time(std::localtime(&in_time_t), "%Y-%m-%d--%I-%M-%S");
-      std::string kernel_name = module->getModuleIdentifier() + "_" + cur_time.str();
+      std::string kernel_name = module->getModuleIdentifier() + "_" + cur_time.str() + "_" + gen_random(12);
       // verify and store llvm
       llvm::legacy::PassManager pm;
       pm.add(llvm::createVerifierPass());