[Bug tree-optimization/58122] New: loops are not evaluated at compile time if loop count > 17

[olegendo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58122

            Bug ID: 58122
           Summary: loops are not evaluated at compile time if loop count
                    > 17
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org

This one was originally reported here:
http://gcc.gnu.org/ml/gcc-help/2013-08/msg00124.html

The original example was:
#include <stdio.h>

template <typename T>
inline T const& max (T const& a, T const& b)
{
  return a < b ? b : a;
}

int main()
{
  long long unsigned sum = 0;

  for (int x = 1; x <= 100000000; x++)
    sum += max (x, x + 1);

  printf("%llu\n", sum);
}

It seems that GCC 4.7 was able to evaluate the loop at compile time and reduce
it to a constant value, but GCC 4.8 fails to do so.

I've also briefly checked with trunk rev 201282 and the problem seems to be
still there.  Here is a reduced test case:

int test (void)
{
  int sum = 0;
  for (int x = 0; x < 100; x++)
    sum += x;

  return sum;
}

I've checked this with an SH cross compiler setup, but I don't think it
matters.
The loops do get eliminated if the number of loop iterations is max. 17, for
both the reduced example and the originally reported case.