https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113372
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Richard Biener from comment #8) > I belive we investigated such workarounds but they didn't seem to work? > Other > cases are concerned with address uses before loops (I think they start > lifetime "correctly" now) but CLOBBERs ending lifetime inside the loop. The > dataflow problem then is confused with the backedge having the object not > live IIRC. > > So what would your workaround do? Not handle address mentions as starting > live but only its (possible) memory uses? I meant in addition to the current cases which start uses (ADDR_EXPRs in the IL, loads and stores) also handle like that uses of SSA_NAMEs which can contain those ADDR_EXPRs. So, say add a mapping from SSA_NAME_VERSION to a bitmap (or vector?) of DECLs and propagate through uses which addresses of decl they (may) refer to and then when add_scope_conflicts_1 sees uses of those SSA_NAMEs, visit_conflict those too. So, say on the testcase from this PR, when seeing ivtmp.40_3 = (unsigned long) &MEM <unsigned long[100]> [(void *)&bitint.6 + 8B]; mark 3 -> bitint.6 # ivtmp.40_39 = PHI <ivtmp.40_3(2), ivtmp.40_38(3)> mark 39 -> bitint.6 # ivtmp.28_40 = PHI <ivtmp.40_3(4), ivtmp.28_41(5)> mark 40 -> bitint.6 _147 = (void *) ivtmp.40_39; mark 147 -> bitint.6 ivtmp.40_38 = ivtmp.40_39 + 16; mark 38 -> bitint.6 _27 = (void *) ivtmp.28_40; mark 27 -> bitint.6 ivtmp.28_41 = ivtmp.28_40 + 16; mark 48 -> bitint.6 _98 = MEM[(unsigned long *)_147 + -8B]; don't do anything, this is a load from it, etc. if (ivtmp.40_38 != _57) again, nothing, etc. _7 = (unsigned long) &bitint.6; mark 7 -> bitint.6 _57 = _7 + 600; mark _57 -> bitint.6 if (ivtmp.40_38 != _57) nothing ivtmp.41_139 = (unsigned long) &MEM <unsigned long[75]> [(void *)&bitint.7 + 8B]; mark 139 -> bitint.7 # ivtmp.41_137 = PHI <ivtmp.41_139(2), ivtmp.41_138(3)> mark 137 -> bitint.7 _146 = (void *) ivtmp.41_137; mark 146 -> bitint.7 ivtmp.41_138 = ivtmp.41_137 + 16; mark 138 -> bitint.7 .DIVMODBITINT (0B, 0, &bitint.6, 6384, &D.2796, -8, &y, -6384); nothing _108 = MEM[(unsigned long *)&bitint.6 + 592B]; nothing, etc. Basically, only handle statements which can propagate address (or pointer-sized integer based on it) of a tracked variable or pointer arithmetics based on that to other SSA_NAMEs. Of course, big question is what kind of propagation to use for that.
