Re: [PATCH 1/2] SH epilogue unwind, dwarf2 pass changes

[Chung-Lin Tang]

On 12/5/23 1:46 AM, Richard Henderson wrote:
> On 05/18/12 03:48, Chung-Lin Tang wrote:
>> @@ -2401,6 +2401,7 @@ scan_trace (dw_trace_info *trace)
>>      {
>>        /* Propagate across fallthru edges.  */
>>        dwarf2out_flush_queued_reg_saves ();
>> +      def_cfa_1 (&this_cfa);
>>        maybe_record_trace_start (insn, NULL);
>>        break;
>>      }
>> @@ -2455,6 +2456,18 @@ scan_trace (dw_trace_info *trace)
>>                cur_cfa = &this_cfa;
>>                continue;
>>              }
>> +          else
>> +            {
>> +              /* If ELT is a annulled branch-taken instruction (i.e. 
>> executed
>> +                 only when branch is not taken), the args_size and CFA 
>> should
>> +                 not change through the jump.  */
>> +              create_trace_edges (control);
>> +
>> +              /* Update and continue with the trace.  */
>> +              add_cfi_insn = insn;
>> +              scan_insn_after (elt);
>> +              continue;
>> +            }
> 
> I think the def_cfa_1 is misplaced.  It should be immediately before
> that last continue.  That mirrors the sort of flow you get via the
> other paths through the loop.

Or possibly moved before the dwarf2out_flush_queued_reg_saves () call in
the patch? (in the save_point_p () break case)  Note I'm only saying
this based on overall ordering of those two routine calls in the loop.

Attached is a testcase (adapted from libgomp) that, with the SH epilogue
unwind patch applied alone, produces the ICE I'm seeing (-O2
-funwind-tables).

This dwarf2 patch, with any of the three new def_cfa_1() call sites
seems to solve it, though you might want to comment on which call site
seems "correct"

Thanks,
Chung-Lin

typedef unsigned long long gomp_ull;
int
foo (gomp_ull *pstart, gomp_ull *pend, int mode,
     gomp_ull next_ull, gomp_ull end_ull, gomp_ull chunk_size_ull)
{
  gomp_ull start, end, chunk, left;
  start = next_ull;
  if (start == end_ull)
    return 0;

  chunk = chunk_size_ull;
  left = end_ull - start;
  if (mode & 2)
    {
      if (chunk < left)
        chunk = left;
    }
  else
    {
      if (chunk > left)
        chunk = left;
    }
  end = start + chunk;
  *pstart = start;
  *pend = end;
  return 1;
}