http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47653
Jeffrey A. Law <law at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
CC| |law at redhat dot com
AssignedTo|unassigned at gcc dot |spop at gcc dot gnu.org
|gnu.org |
--- Comment #2 from Jeffrey A. Law <law at redhat dot com> 2011-02-18 15:36:46
UTC ---
This appears to be a bug in the graphite transformations. Prior to graphite
transformations we have the following function with two nested loops:
# BLOCK 2 freq:139
# PRED: ENTRY [100.0%] (fallthru,exec)
# .MEM_13 = VDEF <.MEM_12(D)>
saved_stack.1_3 = __builtin_stack_save ();
# .MEM_14 = VDEF <.MEM_13>
x.0_4 = __builtin_alloca (256);
goto <bb 8>;
# SUCC: 8 [100.0%] (fallthru,exec)
# BLOCK 3 freq:7901
# PRED: 4 [88.9%] (true,exec)
# SUCC: 4 [100.0%] (fallthru,exec)
# BLOCK 4 freq:8889
# PRED: 3 [100.0%] (fallthru,exec) 9 [100.0%] (fallthru,exec)
# j_23 = PHI <j_7(3), j_5(9)>
# .MEM_24 = PHI <.MEM_15(3), .MEM_6(9)>
# .MEM_15 = VDEF <.MEM_24>
*x.0_4[j_5][j_23] = 0;
j_7 = j_23 + 1;
if (j_7 <= 7)
goto <bb 3>;
else
goto <bb 5>;
# SUCC: 3 [88.9%] (true,exec) 5 [11.1%] (false,exec)
# BLOCK 5 freq:988
# PRED: 4 [11.1%] (false,exec)
# .MEM_19 = PHI <.MEM_15(4)>
# SUCC: 6 [100.0%] (fallthru,exec)
# BLOCK 6 freq:1111
# PRED: 5 [100.0%] (fallthru,exec) 8 [11.1%] (false,exec)
# .MEM_25 = PHI <.MEM_19(5), .MEM_6(8)>
i_8 = j_5 + 1;
if (i_8 <= 7)
goto <bb 7>;
else
goto <bb 10>;
# SUCC: 7 [88.9%] (true,exec) 10 [11.1%] (false,exec)
# BLOCK 7 freq:988
# PRED: 6 [88.9%] (true,exec)
# SUCC: 8 [100.0%] (fallthru,exec)
# BLOCK 8 freq:1111
# PRED: 7 [100.0%] (fallthru,exec) 2 [100.0%] (fallthru,exec)
# j_5 = PHI <i_8(7), 0(2)>
# .MEM_6 = PHI <.MEM_25(7), .MEM_14(2)>
if (j_5 <= 7)
goto <bb 9>;
else
goto <bb 6>;
# SUCC: 9 [88.9%] (true,exec) 6 [11.1%] (false,exec)
# BLOCK 9 freq:988
# PRED: 8 [88.9%] (true,exec)
goto <bb 4>;
# SUCC: 4 [100.0%] (fallthru,exec)
# BLOCK 10 freq:139
# PRED: 6 [11.1%] (false,exec)
# .MEM_16 = VDEF <.MEM_25>
__builtin_stack_restore (saved_stack.1_3);
return 0;
# SUCC: EXIT [100.0%]
Pretty simple stuff.
Graphite transforms it into:
# BLOCK 2 freq:313
# PRED: ENTRY [100.0%] (fallthru,exec)
# .MEM_13 = VDEF <.MEM_12(D)>
saved_stack.1_3 = __builtin_stack_save ();
# .MEM_14 = VDEF <.MEM_13>
x.0_4 = __builtin_alloca (256);
# SUCC: 3 [100.0%] (fallthru)
# BLOCK 3 freq:2500
# PRED: 2 [100.0%] (fallthru) 8 [100.0%] (fallthru,dfs_back)
# graphite_IV.5_11 = PHI <0(2), graphite_IV.5_1(8)>
# .MEM_33 = PHI <.MEM_14(2), .MEM_34(8)>
D.2701_22 = 8 - graphite_IV.5_11;
D.2702_21 = D.2701_22 > 0;
if (D.2702_21 != 0)
goto <bb 4>;
else
goto <bb 7>;
# SUCC: 4 [50.0%] (true) 7 [50.0%] (false)
# BLOCK 4 freq:1250
# PRED: 3 [50.0%] (true)
D.2704_10 = (<unnamed-signed:64>) graphite_IV.5_11;
D.2705_2 = D.2704_10 * 4294967295;
D.2706_18 = D.2705_2 + 7;
# SUCC: 5 [100.0%] (fallthru)
# BLOCK 5 freq:10000
# PRED: 4 [100.0%] (fallthru) 6 [100.0%] (fallthru,dfs_back)
# graphite_IV.6_17 = PHI <0(4), graphite_IV.6_26(6)>
# .MEM_35 = PHI <.MEM_33(4), .MEM_27(6)>
D.2707_28 = (int) graphite_IV.5_11;
D.2708_29 = (int) graphite_IV.5_11;
D.2709_30 = (int) graphite_IV.6_17;
D.2710_31 = D.2708_29 + D.2709_30;
# .MEM_27 = VDEF <.MEM_35>
*x.0_4[D.2707_28][D.2710_31] = 0;
graphite_IV.6_26 = graphite_IV.6_17 + 1;
if (graphite_IV.6_17 < D.2706_18)
goto <bb 6>;
else
goto <bb 7>;
# SUCC: 6 [87.5%] (true) 7 [12.5%] (loop_exit,false)
# BLOCK 6 freq:8750
# PRED: 5 [87.5%] (true)
goto <bb 5>;
# SUCC: 5 [100.0%] (fallthru,dfs_back)
# BLOCK 7 freq:2500
# PRED: 5 [12.5%] (loop_exit,false) 3 [50.0%] (false)
# .MEM_34 = PHI <.MEM_27(5), .MEM_33(3)>
graphite_IV.5_1 = graphite_IV.5_11 + 1;
if (graphite_IV.5_11 < 7)
goto <bb 8>;
else
goto <bb 9>;
# SUCC: 8 [87.5%] (true) 9 [12.5%] (loop_exit,false)
# BLOCK 8 freq:2188
# PRED: 7 [87.5%] (true)
goto <bb 3>;
# SUCC: 3 [100.0%] (fallthru,dfs_back)
# BLOCK 9 freq:313
# PRED: 7 [12.5%] (loop_exit,false)
# .MEM_32 = PHI <.MEM_34(7)>
# .MEM_16 = VDEF <.MEM_32>
__builtin_stack_restore (saved_stack.1_3);
return 0;
# SUCC: EXIT [100.0%]
Of particular interest is the assignment to D.2705_2 in block #4:
D.2705_2 = D.2704_10 * 4294967295;
D.2706_18 = D.2705_2 + 7;
That makes absolutely no sense. Particularly since D.2706_18 is later used to
control loop termination in BB5. Note D.2706 is a 64bit type, so we really
are multiplying by 4294967295. Needless to say this causes the loop
termination condition to do something different than was originally intended.
