[libFuzzer] Include TEMP_MAX_LEN in Fuzzer::PrintStats.

[kcc]

ouch. 10 is too magic.
I've seen hundreds of these printed in a row, i.e. 10 will be too small.
in other cases 10 will be to large.
I wonder if we want to print it as one more number in regular Fuzzer::PrintStats lines, e.g. "lim: 123", like here:
#3145 REDUCE cov: 6 ft: 7 corp: 5/9b lim: 123 exec/s: 0 rss: 37Mb

If so, we'll need to also update the docs to explain what that is.

I am not sure, there might be another better way.

[morehouse]

• Revert "[libFuzzer] Reduce frequency of TEMP_MAX_LEN prints."
• Print TEMP_MAX_LEN in Fuzzer::PrintStats.

[morehouse]

• Remove old TEMP_MAX_LEN print.

[kcc]

LGTM

compiler-rt/lib/fuzzer/FuzzerLoop.cpp

if (size_t N = Corpus.SizeInBytes()) {
       if (N < (1 << 14))
         Printf("/%zdb", N);
       else if (N < (1 << 24))
         Printf("/%zdKb", N >> 10);
       else
         Printf("/%zdMb", N >> 20);
     }
   }
+  if (TmpMaxMutationLen)
+    Printf(" lim: %zd", TmpMaxMutationLen);
   if (Units)
     Printf(" units: %zd", Units);
 
   Printf(" exec/s: %zd", ExecPerSec);
   Printf(" rss: %zdMb", GetPeakRSSMb());
   Printf("%s", End);
 }
 
while (true) {
 
     // Update TmpMaxMutationLen
     if (Options.LenControl) {
       if (TmpMaxMutationLen < MaxMutationLen &&
           TotalNumberOfRuns - LastCorpusUpdateRun >
               Options.LenControl * Log(TmpMaxMutationLen)) {
         TmpMaxMutationLen =
             Min(MaxMutationLen, TmpMaxMutationLen + Log(TmpMaxMutationLen));
-        if (TmpMaxMutationLen <= MaxMutationLen)
-          Printf("#%zd\tTEMP_MAX_LEN: %zd (%zd %zd)\n", TotalNumberOfRuns,
-                 TmpMaxMutationLen, Options.LenControl,
-                 LastCorpusUpdateRun);
         LastCorpusUpdateRun = TotalNumberOfRuns;
       }
     } else {
       TmpMaxMutationLen = MaxMutationLen;
     }
 
     // Perform several mutations and runs.
     MutateAndTestOne();

llvm/docs/LibFuzzer.rst

 ``RELOAD``
   The fuzzer is performing a periodic reload of inputs from the corpus
   directory; this allows it to discover any inputs discovered by other
   fuzzer processes (see `Parallel Fuzzing`_).
 
 Each output line also reports the following statistics (when non-zero):
 
 ``cov:``
-  Total number of code blocks or edges covered by the executing the current
-  corpus.
+  Total number of code blocks or edges covered by executing the current corpus.
 ``ft:``
   libFuzzer uses different signals to evaluate the code coverage:
   edge coverage, edge counters, value profiles, indirect caller/callee pairs, etc.
   These signals combined are called *features* (`ft:`).
 ``corp:``
   Number of entries in the current in-memory test corpus and its size in bytes.
+``lim:``
+  Current limit on the length of new entries in the corpus.  Increases over time
+  until the max length (``-max_len``) is reached.
 ``exec/s:``
   Number of fuzzer iterations per second.
 ``rss:``
   Current memory consumption.
 
 For ``NEW`` events, the output line also includes information about the mutation
 operation that produced the new input: