[Bug c/114831] New: typeof doesn't evaluate expression when it has variably modified type in some cases

["mforney at mforney dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114831

            Bug ID: 114831
           Summary: typeof doesn't evaluate expression when it has
                    variably modified type in some cases
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mforney at mforney dot org
  Target Milestone: ---

C23 introduced typeof, and 6.7.2.5p4 says

> If the type of the operand is a variably modified type, the operand
> is evaluated; otherwise, the operand is not evaluated.

However, gcc doesn't evaluate the operand when it has variably modified type in
some cases.

Consider the following program:

#include <stdio.h>
int n = 1;
int main(void) {
        int a[n], (*p)[n] = 0;
        typeof(puts("&a is variably-modified"), &a) p1;
        typeof(puts("p is variably-modified"), p) p2;
        typeof(puts("p1 is variably-modified"), p1) p3;
        typeof(puts("p2 is variably-modified"), p2) p4;
}

All four of the typeof operands have the same type, int (*)[n]. But when I run
this program it prints just:

p is variably-modified
p2 is variably-modified