[Mesa-dev] [PATCH 19/23] nir: Return progress from nir_convert_from_ssa().

[Jason Ekstrand]

On Thu, Mar 16, 2017 at 2:18 PM, Matt Turner <mattst88 at gmail.com> wrote:

> ---
>  src/compiler/nir/nir.h          |  2 +-
>  src/compiler/nir/nir_from_ssa.c | 21 +++++++++++++++------
>  2 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index db47699..0a127cd 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2587,7 +2587,7 @@ void nir_convert_loop_to_lcssa(nir_loop *loop);
>   * registers.  If false, convert all values (even those not involved in a
> phi
>   * node) to registers.
>   */
> -void nir_convert_from_ssa(nir_shader *shader, bool phi_webs_only);
> +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);
> diff --git a/src/compiler/nir/nir_from_ssa.c b/src/compiler/nir/nir_from_
> ssa.c
> index d2646c6..07fcceb 100644
> --- a/src/compiler/nir/nir_from_ssa.c
> +++ b/src/compiler/nir/nir_from_ssa.c
> @@ -524,18 +524,21 @@ rewrite_ssa_def(nir_ssa_def *def, void *void_state)
>  static bool
>  resolve_registers_block(nir_block *block, struct from_ssa_state *state)
>  {
> +   bool progress = false;
> +
>     nir_foreach_instr_safe(instr, block) {
>        state->instr = instr;
> -      nir_foreach_ssa_def(instr, rewrite_ssa_def, state);
> +      progress |= nir_foreach_ssa_def(instr, rewrite_ssa_def, state);
>

We can't trust the return value here.  rewrite_ssa_def *always* returns
true regardless of whether or not it works.  (It kind-of has to thanks to
the way NIR's function pointer based iteration functions work.)  I think we
need to have a progress boolean in the state structure for this pass.


>
>        if (instr->type == nir_instr_type_phi) {
>           nir_instr_remove(instr);
>           ralloc_steal(state->dead_ctx, instr);
> +         progress = true;
>        }
>     }
>     state->instr = NULL;
>
> -   return true;
> +   return progress;
>  }
>
>  static void
> @@ -756,10 +759,11 @@ resolve_parallel_copies_block(nir_block *block,
> struct from_ssa_state *state)
>     return true;
>  }
>
> -static void
> +static bool
>  nir_convert_from_ssa_impl(nir_function_impl *impl, bool phi_webs_only)
>  {
>     struct from_ssa_state state;
> +   bool progress = false;
>
>     nir_builder_init(&state.builder, impl);
>     state.dead_ctx = ralloc_context(NULL);
> @@ -791,7 +795,7 @@ nir_convert_from_ssa_impl(nir_function_impl *impl,
> bool phi_webs_only)
>     }
>
>     nir_foreach_block(block, impl) {
> -      resolve_registers_block(block, &state);
> +      progress |= resolve_registers_block(block, &state);
>     }
>
>     nir_foreach_block(block, impl) {
> @@ -804,15 +808,20 @@ nir_convert_from_ssa_impl(nir_function_impl *impl,
> bool phi_webs_only)
>     /* Clean up dead instructions and the hash tables */
>     _mesa_hash_table_destroy(state.merge_node_table, NULL);
>     ralloc_free(state.dead_ctx);
> +   return progress;
>  }
>
> -void
> +bool
>  nir_convert_from_ssa(nir_shader *shader, bool phi_webs_only)
>  {
> +   bool progress = false;
> +
>     nir_foreach_function(function, shader) {
>        if (function->impl)
> -         nir_convert_from_ssa_impl(function->impl, phi_webs_only);
> +         progress |= nir_convert_from_ssa_impl(function->impl,
> phi_webs_only);
>     }
> +
> +   return progress;
>  }
>
>
> --
> 2.10.2
>
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