[Bug c/70523] New: Inconsistent casting of floats to unsigned short

[sergey.s at samsung dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70523

            Bug ID: 70523
           Summary: Inconsistent casting of floats to unsigned short
           Product: gcc
           Version: 4.8.4
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sergey.s at samsung dot com
  Target Milestone: ---

Created attachment 38171
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38171&action=edit
Test program

Casting of float expression to unsigned short gives different result when cast
is performed via intermediate variable. Specifically:

#include <stdio.h>

int main()
{
    float f = 1.7857142687f;
    printf("%.10f\n", f);
    unsigned short b = 28;
    unsigned short a = (unsigned short)(b * f);
    printf("%u\n", a);
    float temp = b * f;
    a = (unsigned short)temp;
    printf("%u\n", a);
    return 0;
}
Output:
1.7857142687
49
50
Reproduced only for 32-bit compilation.
On 64-bit compilers both outputs are 50.
Optimization level shall be default.
If optimization level is -O2 or higher both outputs are 50.
Similar to bug 47297, but here value of float expression is well within range
of unsigned short, so behaviour should be defined.