Re: "Uninitialized array" warnings by c++ with -O2

[K <kyb at online dot ru>]

On 06/07/2017 04:56 PM, Andrew Haley wrote:
> On 07/06/17 14:45, K wrote:
> > And I found that that a version which I beleve mustn't have aliasing
> > problems still generates same warnings.
> It still has aliasing problems: you can't make them magically go away
> by using an intermediate uint8_t*.
>
> You're doing this:
>
>           struct udp_pseudo {
>                   uint32_t src;
>                   uint32_t dst;
>                   uint8_t  z;
>                   uint8_t  proto;
>                   uint16_t len;
>           } tmp;
> ...
>
>           auto ret = calc_16bit_checksum_part((uint8_t*)&tmp, sizeof(tmp), 0);
>
>           static uint32_t calc_16bit_checksum_part(uint8_t* buf, int len,  uint32_t ret) {
>           struct ui16{
>                   uint16_t d;
>           };
>           ui16 *ptr = (ui16*)buf;
>
> There's no need for any of this messing about with pointer casts, as has
> been explained.

Sorry, but I still can't get the idea. Cast from udp_pseudo to uint8_t 
doesn't have an aliasing problem (std 8.8) and a cast from uint8_t to 
ui16 still doesn't have an aliasing problem (std  8.6), or may be I 
missed something?


Kirill.