https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80635
--- Comment #61 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:3cf52b87ff6938e30883b8f8f542a638635d507d commit r11-7383-g3cf52b87ff6938e30883b8f8f542a638635d507d Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Feb 25 10:16:55 2021 +0100 vrp: Handle VCE in vrp_simplify_cond_using_ranges [PR80635] > So I wonder what other optimizations are prevented here? > Why does uninit warn with VCE but not with NOP_EXPR? Or does the > warning disappear because of those other optimizations you mention? The optimization that it prevents is in this particular case in tree-vrp.c (vrp_simplify_cond_using_ranges): if (!is_gimple_assign (def_stmt) || !CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt))) return; so it punts on VIEW_CONVERT_EXPR, with NOP_EXPR it optimizes that: _9 = (bool) maybe_a$4_7; if (_9 != 0) into: _9 = (bool) maybe_a$4_7; if (maybe_a$4_7 != 0) Now, if I apply my patch but manually disable this vrp_simplify_cond_using_ranges optimization, then the uninit warning is back, so on the uninit side it is not about VIEW_CONVERT_EXPR vs. NOP_EXPR, both are bad there, uninit wants the guarding condition to be that SSA_NAME and not some demotion cast thereof. We have: # maybe_a$m_6 = PHI <_5(4), maybe_a$m_4(D)(6)> # maybe_a$4_7 = PHI <1(4), 0(6)> ... One of: _9 = VIEW_CONVERT_EXPR<bool>(maybe_a$4_7); if (_9 != 0) or: _9 = (bool) maybe_a$4_7; if (_9 != 0) or: if (maybe_a$4_7 != 0) followed by: goto <bb 11>; [0.00%] else goto <bb 14>; [0.00%] ... <bb 11> [count: 0]: set (maybe_a$m_6); and uninit wants to see that maybe_a$m_4(D) is not used if bb 11 is encountered. This patch fixes it by teaching vrp_simplify_cond_using_ranges to handle VCE (when from an integral type) in addition to NOP_EXPR/CONVERT_EXPR, of course as long as the VCE or demotion doesn't change any values, i.e. when the range of the VCE or conversion operand fits into the target type. 2021-02-25 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/80635 * tree-vrp.c (vrp_simplify_cond_using_ranges): Also handle VIEW_CONVERT_EXPR if modes are the same, innerop is integral and has mode precision. * g++.dg/warn/pr80635-1.C: New test. * g++.dg/warn/pr80635-2.C: New test.
