1. You can't assume VUSE's are must-aliases. The fact that there is a
vuse for something does not imply it is must-used, it implies it is
may-used.
We do not differentiate may-use from must-use in our alias system. You
can do some trivial must-use analysis if you like (by computing
cardinality of points-to set as either single or multiple and
propagating/meeting it in the right place).
Must-use is actually quite rare.
2. " if (!gimple_references_memory_p (def))
+ return;
+"
Is nonsensical the SSA_NAME_DEF_STMT of a vuse must contain a vdef,
and thus must access memory.
On Thu, Aug 14, 2008 at 2:16 PM, Manuel López-Ibáñez
<[EMAIL PROTECTED]> wrote:
> Dear all,
>
> In order to fix PR 179, I need help either understanding why exactly
> the warning is triggered or obtaining a small self-contained testcase
> to reproduce it.
>
> Thanks in advance,
>
> Manuel.
>
> The attached patch triggers the warnings:
>
> /home/manuel/src/trunk/gcc/builtins.c: In function 'fold_builtin_strchr':
> /home/manuel/src/trunk/gcc/builtins.c:11095: error: 'c' is used
> uninitialized in this function
> /home/manuel/src/trunk/gcc/builtins.c: In function 'fold_builtin_memchr':
> /home/manuel/src/trunk/gcc/builtins.c:8963: error: 'c' is used
> uninitialized in this function
>
> Uncommenting the following avoids the warning:
>
> + /*
> + if (is_call_clobbered (var))
> + {
> + var_ann_t va = var_ann (var);
> + unsigned int escape_mask = va->escape_mask;
> + if (escape_mask & ESCAPE_TO_ASM)
> + return false;
> + if (escape_mask & ESCAPE_IS_GLOBAL)
> + return false;
> + if (escape_mask & ESCAPE_IS_PARM)
> + return false;
> + }
> + */
>
> The alias dump is:
>
> fold_builtin_strchr (union tree_node * s1D.68612, union tree_node *
> s2D.68613, union tree_node * typeD.68614)
> {
> union tree_node * temD.68620;
> const charD.1 * rD.68619;
> charD.1 cD.68618;
> const charD.1 * p1D.68617;
> union tree_node * D.68650;
> union tree_node * D.68649;
> long intD.2 D.68648;
> long intD.2 p1.2917D.68647;
> long intD.2 r.2916D.68646;
> union tree_node * D.68644;
> intD.0 D.68641;
> charD.1 c.2915D.68640;
> intD.0 D.68637;
> short unsigned intD.8 D.68631;
> union tree_node * D.68630;
> unsigned charD.10 D.68629;
> unsigned charD.10 D.68627;
>
> # BLOCK 2 freq:10000
> # PRED: ENTRY [100.0%] (fallthru,exec)
> [/home/manuel/src/trunk/gcc/builtins.c : 11095] # VUSE
> <cD.68618_34(D)> { cD.68618 }
> D.68627_3 = validate_argD.45737 (s1D.68612_2(D), 10);
> [/home/manuel/src/trunk/gcc/builtins.c : 11095] if (D.68627_3 == 0)
> goto <bb 10>;
> else
> goto <bb 3>;
> # SUCC: 10 [95.7%] (true,exec) 3 [4.3%] (false,exec)
>
> # BLOCK 3 freq:434
> # PRED: 2 [4.3%] (false,exec)
> [/home/manuel/src/trunk/gcc/builtins.c : 11095] # VUSE
> <cD.68618_34(D)> { cD.68618 }
> D.68629_5 = validate_argD.45737 (s2D.68613_4(D), 8);
> [/home/manuel/src/trunk/gcc/builtins.c : 11095] if (D.68629_5 == 0)
> goto <bb 10>;
> else
> goto <bb 4>;
> # SUCC: 10 [90.0%] (true,exec) 4 [10.0%] (false,exec)
>
> # BLOCK 4 freq:43
> # PRED: 3 [10.0%] (false,exec)
> [/home/manuel/src/trunk/gcc/builtins.c : 11102] # VUSE
> <cD.68618_34(D), SMT.3811D.75594_35(D)> { cD.68618 SMT.3811D.75594 }
> D.68631_6 = s2D.68613_4(D)->baseD.20795.codeD.19700;
> [/home/manuel/src/trunk/gcc/builtins.c : 11102] if (D.68631_6 != 23)
> goto <bb 10>;
> else
> goto <bb 5>;
> # SUCC: 10 [98.3%] (true,exec) 5 [1.7%] (false,exec)
>
> # BLOCK 5 freq:1
> # PRED: 4 [1.7%] (false,exec)
> [/home/manuel/src/trunk/gcc/builtins.c : 11105] # cD.68618_37 = VDEF
> <cD.68618_34(D)>
> # SMT.3811D.75594_38 = VDEF <SMT.3811D.75594_35(D)>
> # SMT.3812D.75595_39 = VDEF <SMT.3812D.75595_36(D)> { cD.68618
> SMT.3811D.75594 SMT.3812D.75595 }
> p1D.68617_8 = c_getstrD.45477 (s1D.68612_2(D));
> [/home/manuel/src/trunk/gcc/builtins.c : 11106] if (p1D.68617_8 != 0B)
> goto <bb 6>;
> else
> goto <bb 10>;
> # SUCC: 6 [20.5%] (true,exec) 10 [79.5%] (false,exec)
>
> # BLOCK 6
> # PRED: 5 [20.5%] (true,exec)
> [/home/manuel/src/trunk/gcc/builtins.c : 11112] # cD.68618_40 = VDEF
> <cD.68618_37>
> # SMT.3811D.75594_41 = VDEF <SMT.3811D.75594_38>
> # SMT.3812D.75595_42 = VDEF <SMT.3812D.75595_39> { cD.68618
> SMT.3811D.75594 SMT.3812D.75595 }
> D.68637_10 = target_char_castD.45483 (s2D.68613_4(D), &cD.68618);
> [/home/manuel/src/trunk/gcc/builtins.c : 11112] if (D.68637_10 != 0)
> goto <bb 10>;
> else
> goto <bb 7>;
> # SUCC: 10 [39.0%] (true,exec) 7 [61.0%] (false,exec)
>
> # BLOCK 7
> # PRED: 6 [61.0%] (false,exec)
> [/home/manuel/src/trunk/gcc/builtins.c : 11115] # VUSE <cD.68618_40>
> { cD.68618 }
> c.2915D.68640_12 = cD.68618;
> [/home/manuel/src/trunk/gcc/builtins.c : 11115] D.68641_13 =
> (intD.0) c.2915D.68640_12;
> [/home/manuel/src/trunk/gcc/builtins.c : 11115] # VUSE <cD.68618_40>
> { cD.68618 }
> rD.68619_14 = strchrD.689 (p1D.68617_8, D.68641_13);
> [/home/manuel/src/trunk/gcc/builtins.c : 11117] if (rD.68619_14 == 0B)
> goto <bb 8>;
> else
> goto <bb 9>;
> # SUCC: 8 [10.1%] (true,exec) 9 [89.9%] (false,exec)
>
> # BLOCK 9
> # PRED: 7 [89.9%] (false,exec)
> [/home/manuel/src/trunk/gcc/builtins.c : 11121] r.2916D.68646_20 =
> (long intD.2) rD.68619_14;
> [/home/manuel/src/trunk/gcc/builtins.c : 11121] p1.2917D.68647_21 =
> (long intD.2) p1D.68617_8;
> [/home/manuel/src/trunk/gcc/builtins.c : 11121] D.68648_22 =
> r.2916D.68646_20 - p1.2917D.68647_21;
> [/home/manuel/src/trunk/gcc/builtins.c : 11121] # cD.68618_46 = VDEF
> <cD.68618_40>
> # SMT.3811D.75594_47 = VDEF <SMT.3811D.75594_41>
> # SMT.3812D.75595_48 = VDEF <SMT.3812D.75595_42> { cD.68618
> SMT.3811D.75594 SMT.3812D.75595 }
> D.68649_23 = size_int_kindD.21427 (D.68648_22, 0);
> [/home/manuel/src/trunk/gcc/builtins.c : 11121] # VUSE <cD.68618_46,
> SMT.3811D.75594_47> { cD.68618 SMT.3811D.75594 }
> D.68650_26 = s1D.68612_2(D)->commonD.20796.typeD.19731;
> [/home/manuel/src/trunk/gcc/builtins.c : 11121] # cD.68618_49 = VDEF
> <cD.68618_46>
> # SMT.3811D.75594_50 = VDEF <SMT.3811D.75594_47>
> # SMT.3812D.75595_51 = VDEF <SMT.3812D.75595_48> { cD.68618
> SMT.3811D.75594 SMT.3812D.75595 }
> temD.68620_27 = fold_build2_statD.21716 (67, D.68650_26,
> s1D.68612_2(D), D.68649_23);
> [/home/manuel/src/trunk/gcc/builtins.c : 11123] # cD.68618_52 = VDEF
> <cD.68618_49>
> # SMT.3811D.75594_53 = VDEF <SMT.3811D.75594_50>
> # SMT.3812D.75595_54 = VDEF <SMT.3812D.75595_51> { cD.68618
> SMT.3811D.75594 SMT.3812D.75595 }
> D.68630_30 = fold_convertD.21753 (typeD.68614_29(D), temD.68620_27);
> # SUCC: 10 [100.0%] (fallthru,exec)
>
> # BLOCK 10 freq:10000, starting at line 0
> # PRED: 3 [90.0%] (true,exec) 4 [98.3%] (true,exec) 6 [39.0%]
> (true,exec) 8 [100.0%] (fallthru,exec) 9 [100.0%] (fallthru,exec) 5
> [79.5%] (false,exec) 2 [95.7%]\
> (true,exec)
> # D.68630_1 = PHI <0B(3), 0B(4), 0B(6), D.68630_18(8),
> D.68630_30(9), 0B(5), 0B(2)>
> return D.68630_1;
> # SUCC: EXIT [100.0%]
>
> }
>
