https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67681
--- Comment #4 from alalaw01 at gcc dot gnu.org --- loopinit introduces the exit phi in much the same way for both -DFOO=0 and -DFOO=1, so the difference is in sccp. In the -DFOO=0 case, sccp does this (removing TODO_cleanup_cfg from pass_data_scev_cprop to make the diff easier, still vectorizes): ;; Function addlog2 (addlog2, funcdef_no=0, decl_uid=2749, cgraph_uid=0, symbol_order=0) + +final value replacement: + i_21 = PHI <i_15(4)> + with + i_21 = (int) _3; + ...[snip]... <bb 10>: - # i_21 = PHI <i_15(4)> + _19 = (unsigned int) i_25; + _18 = (unsigned int) max_7; + _17 = (unsigned int) i_25; + _5 = _18 - _17; + _4 = _5 + _19; + _3 = _4 + 1; + i_21 = (int) _3; In the -DFOO=1 case, sccp doesn't do anything; and adding -fno-tree-scev-cprop prevents vectorization of the -DFOO=0 case.
