[Bug c/80745] New: inconsistent warning: large integer implicitly truncated to unsigned type

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80745

            Bug ID: 80745
           Summary: inconsistent warning: large integer implicitly
                    truncated to unsigned type
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

In four declarations below, the initializer expression is truncated when
assigned to unsigned char.  Yet only the first two initializers are diagnosed
(the warning message could be more helpful but that's the subject of bug
80731).  The same problem affects other unsigned integers besides unsigned
char.

All four initializers should be diagnosed.

$ cat t.c && gcc -S -Wall -Wextra -Wpedantic -Woverflow t.c
#include <limits.h>

unsigned char uc1 = UCHAR_MAX + 1U;
unsigned char uc2 = USHRT_MAX + 1U;
unsigned char uc3 = UINT_MAX + 1U;
unsigned char uc4 = ULONG_MAX + 1LU;

t.c:3:21: warning: large integer implicitly truncated to unsigned type
[-Woverflow]
 unsigned char uc1 = UCHAR_MAX + 1U;
                     ^~~~~~~~~
t.c:4:21: warning: large integer implicitly truncated to unsigned type
[-Woverflow]
 unsigned char uc2 = USHRT_MAX + 1U;
                     ^~~~~~~~~