[Bug target/72767] New: [avr] Some branches report too small insn length

["gjl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72767

            Bug ID: 72767
           Summary: [avr] Some branches report too small insn length
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Created attachment 39039
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39039&action=edit
nops.c: C test case

Some branch instructions report too small instruction length which might lead
to problems if other branches crossing the critical ones use a wrong
instruction sequence.  Outcome can be "relocation truncted to fit" error from
the linker.

Compile test case with

$ avr-gcc -S -dp -Os -mmcu=atmega16 nops.c

In bra_63 there is (should be "length = 2"):

        brne .+2         ;  7   branch  [length = 1]
        rjmp .L1

In bra_2045 (should be "length = 3"):

        brne .+4         ;  7   branch  [length = 2]
        jmp .L6