[Mesa-dev] [PATCH 1/4] nir: Add a small pass to rematerialize derefs per-block

[Jason Ekstrand]

Looks good

On September 19, 2018 22:18:56 "Juan A. Suarez Romero" 
<jasuarez at igalia.com> wrote:

> On Mon, 2018-09-17 at 09:43 -0500, Jason Ekstrand wrote:
>> This pass re-materializes deref instructions on a per-block basis to
>> ensure that every use of a deref occurs in the same block as the
>> instruction which uses it.
>
> Hello!
>
> This patch was commited CCing to 18.2 stable branch.
>
> This patch didn't apply cleanly on 18.2 branch, so I've fixed the conflicts.
>
> Besides this, I've initialized struct variable explicitly to "{ 0 }", 
> instead of
> "{ }", as this was causing an error when building with MSVC.
>
> You can find the patch commited at
>
>
> https://gitlab.freedesktop.org/mesa/mesa/commit/f1305c32c1cd4f7c59ef5dfb2eac33339edabc70
>
>
> The change I did is in line 375.
>
> Feel free to check if there are any error.
>
> Thanks in advance!
>
> 	J.A.
>
>> ---
>>  src/compiler/nir/nir.h       |   1 +
>>  src/compiler/nir/nir_deref.c | 132 +++++++++++++++++++++++++++++++++++
>>  2 files changed, 133 insertions(+)
>>
>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>> index 599f469a714..e0df95c391c 100644
>> --- a/src/compiler/nir/nir.h
>> +++ b/src/compiler/nir/nir.h
>> @@ -3012,6 +3012,7 @@ bool nir_convert_from_ssa(nir_shader *shader, bool 
>> phi_webs_only);
>>
>>  bool nir_lower_phis_to_regs_block(nir_block *block);
>>  bool nir_lower_ssa_defs_to_regs_block(nir_block *block);
>> +bool nir_rematerialize_derefs_in_use_blocks_impl(nir_function_impl *impl);
>>
>>  bool nir_opt_algebraic(nir_shader *shader);
>>  bool nir_opt_algebraic_before_ffma(nir_shader *shader);
>> diff --git a/src/compiler/nir/nir_deref.c b/src/compiler/nir/nir_deref.c
>> index 097ea8f1046..87a54790c95 100644
>> --- a/src/compiler/nir/nir_deref.c
>> +++ b/src/compiler/nir/nir_deref.c
>> @@ -24,6 +24,7 @@
>>  #include "nir.h"
>>  #include "nir_builder.h"
>>  #include "nir_deref.h"
>> +#include "util/hash_table.h"
>>
>>  void
>>  nir_deref_path_init(nir_deref_path *path,
>> @@ -379,3 +380,134 @@ nir_compare_derefs(nir_deref_instr *a, 
>> nir_deref_instr *b)
>>
>>     return result;
>>  }
>> +
>> +struct rematerialize_deref_state {
>> +   bool progress;
>> +   nir_builder builder;
>> +   nir_block *block;
>> +   struct hash_table *cache;
>> +};
>> +
>> +static nir_deref_instr *
>> +rematerialize_deref_in_block(nir_deref_instr *deref,
>> +                             struct rematerialize_deref_state *state)
>> +{
>> +   if (deref->instr.block == state->block)
>> +      return deref;
>> +
>> +   if (!state->cache) {
>> +      state->cache= _mesa_hash_table_create(NULL, _mesa_hash_pointer,
>> +                                            _mesa_key_pointer_equal);
>> +   }
>> +
>> +   struct hash_entry *cached = _mesa_hash_table_search(state->cache, deref);
>> +   if (cached)
>> +      return cached->data;
>> +
>> +   nir_builder *b = &state->builder;
>> +   nir_deref_instr *new_deref =
>> +      nir_deref_instr_create(b->shader, deref->deref_type);
>> +   new_deref->mode = deref->mode;
>> +   new_deref->type = deref->type;
>> +
>> +   if (deref->deref_type == nir_deref_type_var) {
>> +      new_deref->var = deref->var;
>> +   } else {
>> +      nir_deref_instr *parent = nir_src_as_deref(deref->parent);
>> +      if (parent) {
>> +         parent = rematerialize_deref_in_block(parent, state);
>> +         new_deref->parent = nir_src_for_ssa(&parent->dest.ssa);
>> +      } else {
>> +         nir_src_copy(&new_deref->parent, &deref->parent, new_deref);
>> +      }
>> +   }
>> +
>> +   switch (deref->deref_type) {
>> +   case nir_deref_type_var:
>> +   case nir_deref_type_array_wildcard:
>> +   case nir_deref_type_cast:
>> +      /* Nothing more to do */
>> +      break;
>> +
>> +   case nir_deref_type_array:
>> +      assert(!nir_src_as_deref(deref->arr.index));
>> +      nir_src_copy(&new_deref->arr.index, &deref->arr.index, new_deref);
>> +      break;
>> +
>> +   case nir_deref_type_struct:
>> +      new_deref->strct.index = deref->strct.index;
>> +      break;
>> +
>> +   default:
>> +      unreachable("Invalid deref instruction type");
>> +   }
>> +
>> +   nir_ssa_dest_init(&new_deref->instr, &new_deref->dest,
>> +                     deref->dest.ssa.num_components,
>> +                     deref->dest.ssa.bit_size,
>> +                     deref->dest.ssa.name);
>> +   nir_builder_instr_insert(b, &new_deref->instr);
>> +
>> +   return new_deref;
>> +}
>> +
>> +static bool
>> +rematerialize_deref_src(nir_src *src, void *_state)
>> +{
>> +   struct rematerialize_deref_state *state = _state;
>> +
>> +   nir_deref_instr *deref = nir_src_as_deref(*src);
>> +   if (!deref)
>> +      return true;
>> +
>> +   nir_deref_instr *block_deref = rematerialize_deref_in_block(deref, state);
>> +
>> +   nir_instr_rewrite_src(src->parent_instr, src,
>> +                         nir_src_for_ssa(&block_deref->dest.ssa));
>> +   nir_deref_instr_remove_if_unused(deref);
>> +   state->progress = true;
>> +
>> +   return true;
>> +}
>> +
>> +/** Re-materialize derefs in every block
>> + *
>> + * This pass re-materializes deref instructions in every block in which it is
>> + * used.  After this pass has been run, every use of a deref will be of a
>> + * deref in the same block as the use.  Also, all unused derefs will be
>> + * deleted as a side-effect.
>> + */
>> +bool
>> +nir_rematerialize_derefs_in_use_blocks_impl(nir_function_impl *impl)
>> +{
>> +   struct rematerialize_deref_state state = { };
>> +   nir_builder_init(&state.builder, impl);
>> +
>> +   nir_foreach_block(block, impl) {
>> +      state.block = block;
>> +
>> +      /* Start each block with a fresh cache */
>> +      if (state.cache)
>> +         _mesa_hash_table_clear(state.cache, NULL);
>> +
>> +      nir_foreach_instr_safe(instr, block) {
>> +         if (instr->type == nir_instr_type_deref) {
>> +            nir_deref_instr_remove_if_unused(nir_instr_as_deref(instr));
>> +            continue;
>> +         }
>> +
>> +         state.builder.cursor = nir_before_instr(instr);
>> +         nir_foreach_src(instr, rematerialize_deref_src, &state);
>> +      }
>> +
>> +#ifndef NDEBUG
>> +      nir_if *following_if = nir_block_get_following_if(block);
>> +      if (following_if)
>> +         assert(!nir_src_as_deref(following_if->condition));
>> +#endif
>> +   }
>> +
>> +   _mesa_hash_table_destroy(state.cache, NULL);
>> +
>> +   return state.progress;
>> +}