Optimized code stops working

[Jose Xavier]

On the following code I have a packet of 6 bytes that I write to a buffer. I pass the buffer as read_packet function argument. When optimized, the code doesn't work. I only got noise on the UART and even with the debugger I coudn't see the correct values. After some hours of trial and error I decided to select the level 0 of optimization and it started working.

What is the compiler doing?

while (true)
{
    uint32_t received[6];
		
			//received
			read_packet(received);
			//nrf_gpio_pin_toggle(led1);
			//nrf_gpio_pin_toggle(led3);
			app_uart_put(received[1]);
			//app_uart_put(12);
    
    //printf("The contents of the package is %u\n\r", (unsigned int)received);
}

bool read_packet(uint32_t *buffer)
{
    //uint32_t *result = malloc(sizeof(uint32_t)*6);
		static uint32_t result[6];

    NRF_RADIO->EVENTS_READY = 0U;
    // Enable radio and wait for ready
    NRF_RADIO->TASKS_RXEN = 1U;

    while (NRF_RADIO->EVENTS_READY == 0U)
    {
        // wait
    }
    NRF_RADIO->EVENTS_END = 0U;
    // Start listening and wait for address received event
    NRF_RADIO->TASKS_START = 1U;

    // Wait for end of packet or buttons state changed
    while (NRF_RADIO->EVENTS_END == 0U)
    {
        // wait
    }

    if (NRF_RADIO->CRCSTATUS == 1U)
    {
      buffer[0] = packet[0];
			buffer[1] = packet[1];
			buffer[2] = packet[2];
			buffer[3] = packet[3];
			buffer[4] = packet[4];
			buffer[5] = packet[5];
    }
    NRF_RADIO->EVENTS_DISABLED = 0U;
    // Disable radio
    NRF_RADIO->TASKS_DISABLE = 1U;

    while (NRF_RADIO->EVENTS_DISABLED == 0U)
    {
        // wait
    }
    return 1;
}

[Susheel Nuguru]

uint32_t received[6] 

change this to

uint8_t received[6]; 

and

bool read_packet(uint32_t *buffer)

change to

bool read_packet(uint8_t *buffer)

[Susheel Nuguru]

given the code he showed here, there is nothing else optimizable apart from those. So if it works with no optimizations it has to be either variables or arguments. Rest of all the code are volatile device registers. Agree that it is legitimate to copy uint8_t into uint32_t. What happens if you put uint32_t in uint8_t in app_uart_put(received[1]), i am guessing this should be ok too as only LSB is copied and the rest ignored?