------- Comment #6 from rguenth at gcc dot gnu dot org 2010-01-08 15:00 ------- Hm, actually what is wrong is the evolution of l_2_18:
(scalar = l_2_18) (scalar_evolution = {255, +, 0x0ffffffff}_1)) that of l_2_10 is correct: (scalar = l_2_10) (scalar_evolution = (unsigned int) {254, +, 255}_1)) <bb 3>: # l_2_18 = PHI <l_2_10(4), 0x0ffffffff(2)> # prephitmp.10_25 = PHI <g_3.2_7(4), pretmp.9_24(2)> # ivtmp.19_37 = PHI <ivtmp.19_29(4), 255(2)> D.1960_3 = (short unsigned int) l_2_18; g_3.1_5 = (short unsigned int) prephitmp.10_25; D.1963_6 = D.1960_3 | g_3.1_5; g_3.2_7 = (short int) D.1963_6; g_3_lsm.18_11 = g_3.2_7; D.1965_8 = (unsigned char) l_2_18; D.1966_9 = D.1965_8 + 255; l_2_10 = (unsigned int) D.1966_9; ivtmp.19_29 = ivtmp.19_37 - 1; if (ivtmp.19_29 != 0) goto <bb 4>; else goto <bb 5>; <bb 4>: goto <bb 3>; Thus we need to verify we maintain the correct initial condition only? Like for example with Index: tree-scalar-evolution.c =================================================================== --- tree-scalar-evolution.c (revision 155732) +++ tree-scalar-evolution.c (working copy) @@ -1642,6 +1642,15 @@ interpret_loop_phi (struct loop *loop, g init_cond = analyze_initial_condition (loop_phi_node); res = analyze_evolution_in_loop (loop_phi_node, init_cond); + /* Verify we maintained the correct initial condition throughout + possible conversions in the SSA chain. */ + if (res != chrec_dont_know) + { + tree new_init = initial_condition (res); + if (!operand_equal_p (init_cond, new_init, 0)) + return chrec_dont_know; + } + return res; } Maybe too strict in case the returned chrec is wrapped in a conversion operation itself (no idea if that ever happens - at least initial_condition doesn't seem to deal with that during recursion either). I'm going to test that patch. -- rguenth at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- AssignedTo|unassigned at gcc dot gnu |rguenth at gcc dot gnu dot |dot org |org Status|NEW |ASSIGNED Last reconfirmed|2009-12-26 20:00:19 |2010-01-08 15:00:44 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42512