[Valgrind-developers] helgrind: comparison function (too?) sophisticated

[Philippe W. <phi...@sk...>]

I do not understand why the comparison function below is
done like that. It looks very sophisticated compared to the
simpler comparison which is given after.
Is there a reason to have the sophisticated version ?

static Word cmp_WordVecs_for_FM ( UWord wv1W, UWord wv2W )
{
   UWord    i;
   WordVec* wv1    = (WordVec*)wv1W;
   WordVec* wv2    = (WordVec*)wv2W;
   UWord    common = wv1->size < wv2->size ? wv1->size : wv2->size;
   for (i = 0; i < common; i++) {
      if (wv1->words[i] == wv2->words[i])
         continue;
      if (wv1->words[i] < wv2->words[i])
         return -1;
      if (wv1->words[i] > wv2->words[i])
         return 1;
      tl_assert(0);
   }
   /* Ok, the common sections are identical.  So now consider the
      tails.  Both sets are considered to finish in an implied
      sequence of -infinity. */
   if (wv1->size < wv2->size) {
      tl_assert(common == wv1->size);
      return -1; /* impliedly, wv1 contains some -infinitys in places
                    where wv2 doesn't. */
   }
   if (wv1->size > wv2->size) {
      tl_assert(common == wv2->size);
      return 1;
   }
   tl_assert(common == wv1->size);
   return 0; /* identical */
}

The below looks simpler and I believe more efficient.  The order will
be different than of the above, but I have not seen where the specific
order implemented by the above cmp is significant.
At least the helgrind tests give the same results with the below.

static Word cmp_WordVecs_for_FM ( UWord wv1W, UWord wv2W )
{
   UWord    i;
   WordVec* wv1    = (WordVec*)wv1W;
   WordVec* wv2    = (WordVec*)wv2W;

   // WordVecs with smaller size are smaller.
   if (wv1->size < wv2->size) {
      return -1;
   }
   if (wv1->size > wv2->size) {
      return 1;
   }

   // Sizes are equal => order based on content.
   for (i = 0; i < wv1->size; i++) {
      if (wv1->words[i] == wv2->words[i])
         continue;
      if (wv1->words[i] < wv2->words[i])
         return -1;
      if (wv1->words[i] > wv2->words[i])
         return 1;
      tl_assert(0);
   }
   return 0; /* identical */
}