http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51244
--- Comment #3 from Oleg Endo <oleg.e...@t-online.de> 2011-12-27 22:43:11 UTC --- Created attachment 26191 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26191 Proposed patch to improve some of the issues. (In reply to comment #1) > > [...] > > mov #-1,rn > negc rn,rm > tst #255,rm > > which is essentially T_reg = T_reg. Usually combine catches such > situation, but negc might be too complex for combine. > For this case, replacing current movnegt expander by insn, splitter > and peephole something like > > [...] > > the above useless sequence could be removed, though we will miss > the chance that the -1 can be CSE-ed when the cstore value is > used. This will cause a bit worse code for the loop like > > int > foo (int *a, int x, int n) > { > int i; > int count; > > for (i = 0; i < n; i++) > count += (*(a + i) != x); > > return count; > } > Thanks for your ideas and comments. It was really useful. The attached patch removes the useless sequence and still allows the -1 constant to be CSE-ed for such cases as the example function above. I haven't ran all tests on it yet, but CSiBE shows average code size reduction of approx. -0.1% for -m4* with some code size increases in some files. Would something like that be OK for stage 3?
