[Bug c/87857] New: case label does not reduce to an integer constant

[stsp at users dot sourceforge.net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87857

            Bug ID: 87857
           Summary: case label does not reduce to an integer constant
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: stsp at users dot sourceforge.net
  Target Milestone: ---

Hello.

The following example:
---
#include <stdint.h>

int foo(uint64_t a)
{
    switch (a) {
    case (1 << 31):
      return 1;
    }
    return 0;
}

int main(int argc, char *argv[])
{
    return foo(argc);
}
---

doesn't compile with -fsanitize=undefined:
---
$ gcc -Wall -fsanitize=undefined lswitch.c 
lswitch.c: In function ‘foo’:
lswitch.c:6:5: error: case label does not reduce to an integer constant
     case (1 << 31):
---

But if you use g++ or clang with the same
switches, then it compiles fine.