[Bug tree-optimization/66263] [4.9/5/6 Regression] Performance regression from gcc-4.8 and up (trivial sudoku program)

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66263

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
             Status|UNCONFIRMED                 |RESOLVED
      Known to work|                            |4.7.4
         Resolution|---                         |DUPLICATE
      Known to fail|                            |4.8.3, 5.1.0

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed, for me:

4.7.4: 0.77s
4.8.3: 1.5s
5.1: 1.57s

with -O3, time with -O2 didn't regress.  Even with -fno-inline it regresses:

4.7.4 -O3 -fno-inline: 1.7s
5.1 -O3 -fno-inline: 2.3s

Ok, 4.7 unrolls the 

      for (digit = 1; digit <= N; ++digit) {
         if (can_put_digit(row, col, box, digit)) {
            put_digit(row, col, box, digit);
            solve(square+1);
            pop_digit(row, col, box, digit);
         }
      }

loop, so this looks like a duplicate of PR59967.  It also re-orders
basic-blocks in a way that if can_put_digit returns false (which should
be likely in the end) then it just falls thru to the next can_put_digit call.

With inlining the non-pure call is the recursion to solve ().

*** This bug has been marked as a duplicate of bug 59967 ***