------- Comment #20 from rakdver at kam dot mff dot cuni dot cz 2007-11-08 14:46 ------- Subject: Re: [4.3 regression] udivdi3 counterproductive, unwarranted use
> ------- Comment #19 from manu at gcc dot gnu dot org 2007-11-08 14:22 ------- > (In reply to comment #16) > > One possible solution would be to annotate the division by the expected > > value > > of the result. Division expanders then may decide whether to expand to > > machine > > instruction/libcall or to check for small values of the result in if-guards > > first. > > > > Well, that won't achieve at all what the user wants, that is, to not get a > call > to __udividi3. However, it would avoid calling the division most of the time, i.e., for performance this would be a possible solution. > There are 2 issues here: > > 1) GCC replaces the loop by division. This may or may not be more efficient. > In > this case, it is not. In many other cases, it is. The code performing the replacement should probably check what is the expected # of iterations of the loop, and compute which way is more efficient. However, it is a bit difficult to get this work correctly. > 2) The user does not want a call to __udividi3. There is nothing wrong with calling __udividi3, once the division is introduced. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32044
