------- Comment #21 from tobi at gcc dot gnu dot org 2009-08-14 21:44 ------- (In reply to comment #19) > (In reply to comment #17) > From quickly looking at the code, the copy to real_to is probably unnecessary > because loop bounds are passed through gfc_evaluate_now before calling > gfc_trans_simple_do ( never mind if it gives the good assembly :) ).
I suspected that this reason wouldn't hold. Place a wrong statement on the internet, you will no after a few seconds :) The real reason is that no pointer to the upper bound that is compared against can escape, so that better assembler will result. I will update the comment. > Couldn't the same be made in gfc_trans_do ? There, the number of iterations is calculated before the loop, so the problem doesn't arise. I'm guessing that before my patch, gfc_trans_simple_do actually lead to a net slowdown of the generated code. Lesson learnt: don't optimize without measuring or at least looking at the generated code :) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31593
