[profile] Remove useless msync when dumping gcda files

[calixte]

Summary

According the mmap man page (https://man7.org/linux/man-pages/man2/mmap.2.html) is only required to precisely control updates, so we can safely remove it.
Since gcda files are dumped just before to call exec** functions, dump need to be fast.
On my computer, Firefox built with --coverage needs ~1min40 to display something and in removing msync it needs ~8s.
The slowdown is probably because the directory where data are dumped is on a spinning disk.

[serge-sans-paille]

I have the same understanding as @calixte when reading the manpage: munmap forces the write and calling msync right before is redundant.

[serge-sans-paille]

That being said, I would not expect such a speedup...

[serge-sans-paille]

No more feedback, let's take the manpage as the tablets of the law here .

compiler-rt/lib/profile/GCDAProfiling.c

#if defined(_WIN32)
 
   if (!CloseHandle(mmap_handle)) {
     fprintf(stderr, "profiling: %s: cannot close file mapping handle: %lu\n",
             filename, GetLastError());
   }
 
   mmap_handle = NULL;
 #else
-  if (msync(write_buffer, file_size, MS_SYNC) == -1) {
+  if (munmap(write_buffer, file_size) == -1) {
     int errnum = errno;
-    fprintf(stderr, "profiling: %s: cannot msync: %s\n", filename,
+    fprintf(stderr, "profiling: %s: cannot munmap: %s\n", filename,
             strerror(errnum));
   }
-
-  /* We explicitly ignore errors from unmapping because at this point the data
-   * is written and we don't care.
-   */
-  (void)munmap(write_buffer, file_size);
 #endif
 
   write_buffer = NULL;
   file_size = 0;
 }
 
 /*
  * --- LLVM line counter API ---