[Bug middle-end/57886] New: Invalid folding of (float)-x to -(float)x

[matz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57886

            Bug ID: 57886
           Summary: Invalid folding of (float)-x to -(float)x
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: matz at gcc dot gnu.org

Came up in IRC, GCC invalidly moves a conversion innerwards:

% cat x.c
extern void abort (void);
float global;
int main()
{
  unsigned long z = 1;
  float x = -z;
  global = x;
  if (global < 0)
    abort ();
  return 0;
}
% gcc x.c && ./a.out
Aborted

This is because GCC transforms the initializer of x (float)-z, into
-(float)z, even though z is an unsigned int.  -z is always positive, but
due to this x will be -1.