[Bug c/33675] New: Badly optimized negations on x86 with -frounding-math

[bagnara at cs dot unipr dot it]

If you compile the function

void assign2(float* a, double b) {
  volatile float v = -b;
  *a = -v;
}

you will see that GCC 4.1.2, e.g., at -O2, produces

        fldl    12(%ebp)
        fchs
        movl    8(%ebp), %eax
        fstps   -20(%ebp)
        flds    -20(%ebp)
        fstps   -4(%ebp)
        flds    -4(%ebp)
        fchs
        fstps   (%eax)

insted of simply

        fldl    12(%ebp)
        fchs
        fstps   -4(%ebp)
        flds    -4(%ebp)
        fchs
        fstps   (%eax)


-- 
           Summary: Badly optimized negations on x86 with -frounding-math
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bagnara at cs dot unipr dot it


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33675