[Mesa-dev] [PATCH 007/133] nir: add a validation pass

[Connor Abbott]

On Thu, Dec 18, 2014 at 2:01 AM, Eric Anholt <eric at anholt.net> wrote:
> Jason Ekstrand <jason at jlekstrand.net> writes:
>
>> From: Connor Abbott <connor.abbott at intel.com>
>>
>> This is similar to ir_validate.cpp.
>>
>> v2: Jason Ekstrand <jason.ekstrand at intel.com>:
>>    whitespace fixes
>
> I have again not reviewed the control flow bits.  Couple of questions I
> had, though:
>
>> +static void
>> +validate_var_use(nir_variable *var, validate_state *state)
>> +{
>> +   if (var->data.mode == nir_var_local) {
>> +      struct hash_entry *entry =
>> +         _mesa_hash_table_search(state->var_defs, _mesa_hash_pointer(var),
>> +                                 var);
>> +
>> +      assert(entry);
>> +      assert((nir_function_impl *) entry->data == state->impl);
>> +   }
>> +}
>
> Is there guaranteed to be a def of a local variable before a use?  It
> would be undefined execution behavior, but not assertion failure
> quality, right?

Yes, that's correct - there are no guarantees about this for variables
and registers. For SSA values, the definition should always dominate
the use (see the TODO about that) because a lot of SSA algorithms
assume that, so we model the use-before-def case by pointing the use
to a nir_ssa_undef_instr.

>
>> +static void
>> +postvalidate_reg_decl(nir_register *reg, validate_state *state)
>> +{
>> +   struct hash_entry *entry = _mesa_hash_table_search(state->regs,
>> +                                                      _mesa_hash_pointer(reg),
>> +                                                      reg);
>> +
>> +   reg_validate_state *reg_state = (reg_validate_state *) entry->data;
>> +
>> +   if (reg_state->uses->entries != reg->uses->entries) {
>> +      printf("extra entries in register uses:\n");
>> +      struct set_entry *entry;
>> +      set_foreach(reg->uses, entry) {
>> +         struct set_entry *entry2 =
>> +            _mesa_set_search(reg_state->uses, _mesa_hash_pointer(entry->key),
>> +                             entry->key);
>> +
>> +         if (entry2 == NULL) {
>> +            printf("%p\n", entry->key);
>> +         }
>> +      }
>> +
>> +      abort();
>> +   }
>> +
>> +   if (reg_state->defs->entries != reg->defs->entries) {
>> +      printf("extra entries in register defs:\n");
>> +      struct set_entry *entry;
>> +      set_foreach(reg->defs, entry) {
>> +         struct set_entry *entry2 =
>> +            _mesa_set_search(reg_state->defs, _mesa_hash_pointer(entry->key),
>> +                             entry->key);
>> +
>> +         if (entry2 == NULL) {
>> +            printf("%p\n", entry->key);
>> +         }
>> +      }
>
> Couldn't these failures go the other way and there be, for example,
> defs that weren't tracked in the reg?
>
> (Not necessarily important to fix, since you'll at least get the
> abort())

Yeah, the point here is that we've already validated that all the
actual definitions (i.e. everything in reg_state->defs) are already in
reg->defs, so once we've gotten to this point the only possible reason
for them not being the same is that reg->defs has extra entries, which
we check for here.

>
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