------- Comment #5 from dann at godzilla dot ics dot uci dot edu 2006-05-03 18:54 ------- IMO Comment #4 does not look close enough at what is actually happening. IMO tree-ch is the root cause here.
The code looks like this before .ch Before .ch goto <bb 2> (<L1>); <L0>:; D.1301_54 = Int_Loc.0_4 * 200; D.1302_55 = (int[50] *) D.1301_54; D.1303_56 = Arr_2_Par_Ref_30 + D.1302_55; (*D.1303_56)[Int_Index_1] = Int_Loc_3; Int_Index_58 = Int_Index_1 + 1; # Int_Index_1 = PHI <Int_Loc_3(0), Int_Index_58(1)>; <L1>:; D.1305_26 = Int_Loc_3 + 1; if (Int_Index_1 <= D.1305_26) goto <L0>; else goto <L2>; <L2>:; after .ch it looks like this: D.1305_41 = Int_Loc_3 + 1; if (Int_Loc_3 <= D.1305_41) goto <L0>; else goto <L2>; <-- this just complicates the CFG. Look below to see what are the effects of doing this in later passes. Plus just look at the comparison ... # Int_Index_37 = PHI <Int_Index_58(1), Int_Loc_3(0)>; <L0>:; D.1301_54 = Int_Loc.0_4 * 200; D.1302_55 = (int[50] *) D.1301_54; D.1303_56 = Arr_2_Par_Ref_30 + D.1302_55; (*D.1303_56)[Int_Index_37] = Int_Loc_3; Int_Index_58 = Int_Index_37 + 1; D.1305_26 = Int_Loc_3 + 1; if (D.1305_26 >= Int_Index_58) goto <L0>; else goto <L2>; <L2>:; Given the above CFG, critical edge splitting transforms this into: D.1305_41 = Int_Loc_3 + 1; if (Int_Loc_3 <= D.1305_41) goto <L6>; else goto <L7>; <L7>:; goto <bb 2> (<L2>); <L6>:; # Int_Index_37 = PHI <Int_Index_58(5), Int_Loc_3(3)>; <L0>:; D.1301_54 = Int_Loc.0_4 * 200; D.1302_55 = (int[50] *) D.1301_54; D.1303_56 = Arr_2_Par_Ref_30 + D.1302_55; (*D.1303_56)[Int_Index_37] = Int_Loc_3; Int_Index_58 = Int_Index_37 + 1; if (D.1305_41 >= Int_Index_58) goto <L8>; else goto <L9>; <L8>:; goto <bb 1> (<L0>); <L9>:; <L2>:; Given the above CFG PRE will dutifully fill with code a lot of the empty basic blocks: after pre D.1305_41 = Int_Loc_3 + 1; if (Int_Loc_3 <= D.1305_41) goto <L6>; else goto <L7>; <L7>:; pretmp.34_45 = Int_Loc.0_4 * 200; pretmp.36_57 = (int[50] *) pretmp.34_45; pretmp.38_25 = Arr_2_Par_Ref_30 + pretmp.36_57; goto <bb 2> (<L2>); <L6>:; pretmp.30_26 = Int_Loc.0_4 * 200; pretmp.31_19 = (int[50] *) pretmp.30_26; pretmp.32_1 = pretmp.31_19 + Arr_2_Par_Ref_30; # Int_Index_37 = PHI <Int_Index_58(5), Int_Loc_3(3)>; <L0>:; D.1301_54 = pretmp.30_26; D.1302_55 = pretmp.31_19; D.1303_56 = pretmp.32_1; (*D.1303_56)[Int_Index_37] = Int_Loc_3; Int_Index_58 = Int_Index_37 + 1; if (D.1305_41 >= Int_Index_58) goto <L8>; else goto <L9>; <L8>:; goto <bb 1> (<L0>); <L9>:; # prephitmp.39_23 = PHI <D.1303_56(6), pretmp.38_25(4)>; # prephitmp.37_53 = PHI <D.1302_55(6), pretmp.36_57(4)>; # prephitmp.35_49 = PHI <D.1301_54(6), pretmp.34_45(4)>; <L2>:; Now when using -fno-tree-ch before critical edge splitting the code looks like this: goto <bb 2> (<L1>); <L0>:; D.1301_54 = Int_Loc.0_4 * 200; D.1302_55 = (int[50] *) D.1301_54; D.1303_56 = Arr_2_Par_Ref_30 + D.1302_55; (*D.1303_56)[Int_Index_1] = Int_Loc_3; Int_Index_58 = Int_Index_1 + 1; # Int_Index_1 = PHI <Int_Loc_3(0), Int_Index_58(1)>; <L1>:; D.1305_26 = Int_Loc_3 + 1; if (Int_Index_1 <= D.1305_26) goto <L0>; else goto <L2>; <L2>:; after crited it looks like this: (i.e. no change) goto <bb 2> (<L1>); <L0>:; D.1301_54 = Int_Loc.0_4 * 200; D.1302_55 = (int[50] *) D.1301_54; D.1303_56 = Arr_2_Par_Ref_30 + D.1302_55; (*D.1303_56)[Int_Index_1] = Int_Loc_3; Int_Index_58 = Int_Index_1 + 1; # Int_Index_1 = PHI <Int_Loc_3(0), Int_Index_58(1)>; <L1>:; D.1305_26 = Int_Loc_3 + 1; if (Int_Index_1 <= D.1305_26) goto <L0>; else goto <L2>; <L2>:; and after PRE goto <bb 2> (<L1>); <L0>:; D.1301_54 = pretmp.31_49; D.1302_55 = pretmp.32_45; D.1303_56 = pretmp.33_41; (*D.1303_56)[Int_Index_1] = Int_Loc_3; Int_Index_58 = Int_Index_1 + 1; # Int_Index_1 = PHI <Int_Loc_3(0), Int_Index_58(1)>; <L1>:; D.1305_26 = pretmp.30_19; if (Int_Index_1 <= D.1305_26) goto <L0>; else goto <L2>; <L2>:; -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26944
