PATCH: Bad signed int to long long conversion

[Vincent Lefevre]

On 2011-12-01 14:12:41 +0100, Vincent Lefevre wrote:
> On 2011-12-01 13:13:05 +0100, Torbjorn Granlund wrote:
> > The GCC bug report involves two operand sizes, and is indeed invalid.
> 
> AFAIK, the VRP logic is not based on these two operand sizes.
> What matters here is that the subtraction (where only one type
> is involved) overflows and GCC assumes that this cannot occur
> in a correct program.

Here's a testcase showing that even with a single type, one gets
problems with -LONG_MIN:

#include <stdio.h>
#include <limits.h>

int foo (long i)
{
  long j = i < 0 ? -i : i;
  return j >= 0;
}

int main (void)
{
  volatile long i = LONG_MIN;

  printf ("%d\n", foo (i));
  return 0;
}

ypig:~> gcc tst.c -o tst; ./tst
0
ypig:~> gcc -O2 tst.c -o tst; ./tst
1

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