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[RFH] PR middle-end/179 gcc -O2 -Wuninitialized missing warning with &var

From: "Manuel López-Ibáñez" <lopezibanez at gmail dot com>
To: "GCC Development" <gcc at gcc dot gnu dot org>
Cc: "Richard Guenther" <richard dot guenther at gmail dot com>, "Diego Novillo" <dnovillo at google dot com>, "Gabriel Dos Reis" <gdr at integrable-solutions dot net>
Date: Thu, 14 Aug 2008 20:16:28 +0200
Subject: [RFH] PR middle-end/179 gcc -O2 -Wuninitialized missing warning with &var

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%]

}

Attachment: fix-pr179-try5.diff
Description: Text document

Follow-Ups:
- Re: [RFH] PR middle-end/179 gcc -O2 -Wuninitialized missing warning with &var
  - From: Daniel Berlin

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