[Bug c/48874] New: Sign of zeros sometimes lost in literals

[jb at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48874

           Summary: Sign of zeros sometimes lost in literals
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: j...@gcc.gnu.org


Consider

#include <stdio.h>
#include <complex.h>

int main()
{
  double _Complex a = 0.0 + I*0.0;
  double _Complex b = 0.0 - I*0.0;
  double _Complex c = -0.0 + I*0.0;
  double _Complex d = -0.0 - I*0.0;
  printf("a= (%g,%g)\n", creal(a), cimag(a));
  printf("b= (%g,%g)\n", creal(b), cimag(b));
  printf("c= (%g,%g)\n", creal(c), cimag(c));
  printf("d= (%g,%g)\n", creal(d), cimag(d));
}

This program, compiled with "gcc zero1.c -O2 -pedantic -Wall -std=c99" (or
-std=gnu99) prints

a= (0,0)
b= (0,-0)
c= (0,0)
d= (-0,-0)

That is, the sign of the real part of "c" is lost. Add -fdump-tree-original to
the compile flags shows the dump as

;; Function main (null)
;; enabled by -tree-original

{
  complex double a = __complex__ (0.0, 0.0);
  complex double b = __complex__ (0.0, -0.0);
  complex double c = __complex__ (0.0, 0.0);
  complex double d = __complex__ (-0.0, -0.0);

    complex double a = __complex__ (0.0, 0.0);
    complex double b = __complex__ (0.0, -0.0);
    complex double c = __complex__ (0.0, 0.0);
    complex double d = __complex__ (-0.0, -0.0);
  printf ((const char * restrict) "a= (%g,%g)\n", REALPART_EXPR <a>,
IMAGPART_EXPR <a>);
  printf ((const char * restrict) "b= (%g,%g)\n", REALPART_EXPR <b>,
IMAGPART_EXPR <b>);
  printf ((const char * restrict) "c= (%g,%g)\n", REALPART_EXPR <c>,
IMAGPART_EXPR <c>);
  printf ((const char * restrict) "d= (%g,%g)\n", REALPART_EXPR <d>,
IMAGPART_EXPR <d>);
}
return 0;

so it seems the negative sign of the real part of c is lost already in the
frontend.

Version of the compiler: 

gcc version 4.7.0 20110504 (experimental) (GCC) 

Target: x86_64-unknown-linux-gnu