[Bug tree-optimization/123602] New: ICE: SSA corruption during RTL pass: expand with -O2 and -std=c++20 flag

[jirehguo at tju dot edu.cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123602

            Bug ID: 123602
           Summary: ICE: SSA corruption during RTL pass: expand with -O2
                    and -std=c++20 flag
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jirehguo at tju dot edu.cn
  Target Milestone: ---

Compiler Explorer: https://godbolt.org/z/G7x58WzKT
The following c++ code crash gcc trunk with -O2 flag.
Goes back to gcc 8.1 with -O2 flag.


Code:
```cpp
#include <csetjmp>
#include <vector>
int ARRAY_SIZE;
jmp_buf jump_buffer;
template <typename> struct Inline { static void apply(int); };
struct CleanupContext {
  jmp_buf env;
};
int main() {
  {
    for (int i; i;) {
      CleanupContext context;
      if (setjmp(context.env)) {
        asm("memory");
        std::vector<int> arr(ARRAY_SIZE, 1);
        for (int j = 3; j; ++j) {
          int i10 = arr[j - 1];
          if (setjmp(jump_buffer))
            ;
          Inline<int>::apply(i10);
        }
      }
    }
  }
}

```

Stack dump:
```

Unable to coalesce ssa_names 6 and 8 which are marked as MUST COALESCE.
j_6(ab) and  j_8(ab)
during RTL pass: expand
<source>: In function 'int main()':
<source>:9:5: internal compiler error: SSA corruption
    9 | int main() {
      |     ^~~~
0x292a498 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
        ???:0
0x291f25b internal_error(char const*, ...)
        ???:0
0x167a424 coalesce_ssa_name(_var_map*)
        ???:0
0x1601f34 rewrite_out_of_ssa(ssaexpand*)
        ???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1
```