[Bug sanitizer/65365] New: false positive signed negation

[joerg.richter@pdv-fs.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65365

            Bug ID: 65365
           Summary: false positive signed negation
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: joerg.richter@pdv-fs.de
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org

cat > t.c <<EOF
int neg( unsigned v )
{
  return -(int)(v-1)-1;
}

int main( int, char** )
{
  neg( 2147483648u );
  return 0;
}
EOF

g++ -o t t.c -fsanitize=undefined
./t



Gives this output:
t.c:3:22: runtime error: negation of -2147483648 cannot be represented in type
'int'; cast to an unsigned type to negate this value to itself

AFAIKS all operations are defined.

If the subtraction with "-1" is removed the error about negation disappears.