How to update reg_dead notes

[Georg-Johann Lay]

Am 02/24/2015 um 06:06 PM schrieb Eric Botcazou:
>> Could you give me some advice on correct usage of df or even more preferred
>> point me to a comprehensible documentation of df which is more complete than
>> in df-core.c?
>
> Take a look at the c6x and mep ports.
>

Thanks for the hint.  I changed the execute method to:

unsigned int execute ()
   {
     compute_bb_for_insn ();
     //df_clear_flags (DF_LR_RUN_DCE);
     df_note_add_problem ();
     df_analyze ();
     df_finish_pass (false);

     return 0;
   }

bit it keeps aborting.  Actually I am just copy pasting code from some other 
passes / BEs, but these places also don't have explanation for why they must 
use, may use, must not use specific functions.

Compiling the mentioned test case from libgcc with -Os (so that less insns are 
left over) and patching df-scan.c:df_refs_verify to print the refs just before 
it does gcc_assert (0):

new_ref = { u-1(18){ }}
*old_rec = { u-1(18){ }u-1(19){ }u-1(24){ }u-1(25){ }}
libgcc2-addvsi3.c: In function '__addvhi3':
libgcc2-addvsi3.c:1514:1: internal compiler error: in df_refs_verify, at 
df-scan.c:4338

In df_insn_refs_verify which is in the call chain of df_refs_verify, insn reads:

(insn 21 19 22 5 (parallel [
             (set (cc0)
                 (compare (reg/v:HI 18 r18 [orig:48 a ] [48])
                     (reg/v:HI 24 r24 [orig:46 w ] [46])))
             (clobber (scratch:QI))
         ]) libgcc2-addvsi3.c:1511 408 {*cmphi}
      (expr_list:REG_DEAD (reg/v:HI 18 r18 [orig:48 a ] [48])
         (nil)))

r18 and r24 are ordinary general-purpose hard registers.


The latest pass which runs before the crash is .split5, i.e. 
recog.c::pass_split_for_shorten_branches which executes split_all_insns_noflow 
which in turn reads:

/* Same as split_all_insns, but do not expect CFG to be available.
    Used by machine dependent reorg passes.  */

unsigned int
split_all_insns_noflow (void)
{ ...

Does this mean CFG is (or might be) messed up after this pass and this is the 
reason for why df crashes because df needs correct CFG?

Johann