Works with -O0, breaks on -O1

output.log

C:\dev\20_CPP\test-seh-exceptions>clang++.exe -O0 -g test_seh_exceptions.cpp -o test_seh_exceptions_O0.exe

C:\dev\20_CPP\test-seh-exceptions>test_seh_exceptions_O0.exe
in __try
in __finally
ret 2, i 5
in __try
in __catch
in __finally
ret -2
Exit 0

C:\dev\20_CPP\test-seh-exceptions>clang++.exe -O1 -g test_seh_exceptions.cpp -o test_seh_exceptions_O1.exe

C:\dev\20_CPP\test-seh-exceptions>test_seh_exceptions_O1.exe
in __try
in __finally
ret -2, i 5
in __try
in __catch
in __finally
ret -2
Exit 0

test_seh_exceptions.cpp

#include <cstdio>
#include <Windows.h>

extern "C" {
__attribute__((__used__))
LONG WINAPI SehExceptionHandler(EXCEPTION_POINTERS * lpEP) {
    return EXCEPTION_EXECUTE_HANDLER;
}
}


__declspec(noinline)
void UnsafeFunction(int* ptr) {
    (*ptr)++;
}

__declspec(noinline)
int test_SEH_TryCatch(int* ptr)
{
#define suffix "testsehasm"

    volatile int r = 0;
    __asm__ __volatile__ ( \
    ".l_try_begin_" suffix ":\n" \
    ".seh_handler __C_specific_handler, @except\n" \
    ".seh_handlerdata\n" \
    ".long 1\n" \
    ".rva .l_try_begin_" suffix ", .l_try_end_" suffix ", SehExceptionHandler, .l_catch_" suffix "\n" \
    ".text\n" \
    );
    {
        std::printf("in __try\n");
        UnsafeFunction(ptr);
        r = 1;
    }
    asm ( \
    "nop\n" \
    ".l_try_end_" suffix ":\n" \
    "nop\n" \
    "jmp .l_finally_" suffix "\n" \
    "nop\n" \
    ".l_catch_" suffix ":\n" \
    "nop\n" \
    );
    {
        std::printf("in __catch\n");
        r = -1;
    }
    asm ( \
    "nop\n" \
    ".l_finally_" suffix ":" \
    "nop\n" \
    );
    {
        std::printf("in __finally\n");
        r *= 2;
    }
    asm ( \
    "nop\n" \
    ".l_exit_fn_" suffix ":" \
    "nop\n" \
    );
    return r;
}

int main(int, char*[]) {
    {
        int i = 4;
        int r = test_SEH_TryCatch(&i);
        std::printf("ret %d, i %d\n", r, i);
    }
    {
        int *p = nullptr;
        int r = test_SEH_TryCatch(p);
        std::printf("ret %d\n", r);
    }
    std::printf("Exit 0\n");
    return 0;
}