[Bug tree-optimization/23129] New: VRP propagates division of antiranges incorrectly

[rmorganl at u dot washington dot edu]

VRP miscompiles the following testcase at -O2:


#include <stdlib.h>

void test(int x, int y)
{
        int c;

        if (x == 1) abort();
        if (y == 1) abort();

        c = x / y;

        if (c != 1) abort();
}

int main()
{
        test(2, 2);
}


The t27.vrp dump shows what happens:

...
c_3: ~[1, 1]  EQUIVALENCES: { } (0 elements)
x_4: ~[1, 1]  EQUIVALENCES: { x_1 } (1 elements)
y_5: ~[1, 1]  EQUIVALENCES: { y_2 } (1 elements)

Folding predicate c_3 != 1 to 1
...

VRP concludes that since x != 1 and y != 1, then x / y != 1, which is clearly
incorrect. This results in the last abort being made unconditional.

-- 
           Summary: VRP propagates division of antiranges incorrectly
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rmorganl at u dot washington dot edu
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-cygwin
  GCC host triplet: i686-pc-cygwin
GCC target triplet: i686-pc-cygwin


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23129