[Bug c++/60840] New: avr-g++: Incorrect avr assembler code generation

["dragontears at bk dot ru" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60840

            Bug ID: 60840
           Summary: avr-g++: Incorrect avr assembler code generation
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dragontears at bk dot ru

avr-g++ produces incorrect assembler output. Sample code:


#include <stdint.h>
#include <avr/io.h>

struct test
{
    uint8_t shift;
};

volatile const test* smth = 0;

int main(void)
{
    while(1)
    {
        if(smth == 0)
            continue;

        PORTB |= (1 << smth->shift);
    }
}


Generated assembler output contains a single check if smth == 0 and an endless
loop right after that. RJMP contains incorrect address:

...
0000007c <main>:
  7c:    21 e0           ldi    r18, 0x01    ; 1
  7e:    30 e0           ldi    r19, 0x00    ; 0
  80:    e0 91 60 00     lds    r30, 0x0060
  84:    f0 91 61 00     lds    r31, 0x0061
  88:    30 97           sbiw    r30, 0x00    ; 0
  8a:    09 f4           brne    .+2          ; 0x8e <main+0x12>
  8c:    ff cf           rjmp    .-2          ; 0x8c <main+0x10> //HERE IT IS
...


But if you put a simple NOP instruction before "continue", you get correct
output:

...
0000007c <main>:
  7c:    21 e0           ldi    r18, 0x01    ; 1
  7e:    30 e0           ldi    r19, 0x00    ; 0
  80:    e0 91 60 00     lds    r30, 0x0060
  84:    f0 91 61 00     lds    r31, 0x0061
  88:    30 97           sbiw    r30, 0x00    ; 0
  8a:    11 f4           brne    .+4          ; 0x90 <main+0x14>
  8c:    00 00           nop
  8e:    f8 cf           rjmp    .-16         ; 0x80 <main+0x4> //THE POINTER
IS GOOD NOW
...


Seems that this bug is not dependent on compiler options. Probably, avr-gcc has
this bug too (haven't checked that).