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From: "vincent-gcc at vinc17 dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/51721] New: -Warray-bounds false positives and inconsistencies
Date: Sat, 31 Dec 2011 01:51:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51721

             Bug #: 51721
           Summary: -Warray-bounds false positives and inconsistencies
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincent-gcc@vinc17.net


I get strange -Warray-bounds false positives on the following code:

static int a[10], b[10], c[10], d[10];

unsigned int f (unsigned int v)
{
  return v == 17 ? 11 : v;
}

unsigned int g (unsigned int v)
{
  return v == 17 ? 17 : v;
}

void t (unsigned int s)
{
  if (s >> 1 == 0)
    {
      a[f(s)] = 0;
      a[f(s)] = 0;
      b[f(s)] = 0;
      c[g(s)] = 0;
      c[g(s)] = 0;
      d[H(s)] = 0;
    }
}

With gcc (Debian 4.6.2-9) 4.6.2 on a Debian/x86_64 machine:

$ gcc-snapshot -O2 -Warray-bounds -c bounds.c -DH=f
bounds.c: In function 't':
bounds.c:17:8: warning: array subscript is above array bounds [-Warray-bounds]
bounds.c:19:8: warning: array subscript is above array bounds [-Warray-bounds]
bounds.c:20:8: warning: array subscript is above array bounds [-Warray-bounds]

$ gcc-snapshot -O2 -Warray-bounds -c bounds.c -DH=g
bounds.c: In function 't':
bounds.c:17:8: warning: array subscript is above array bounds [-Warray-bounds]

Note: line 17 is the first "a[f(s)] = 0;".