On 11/7/18 9:36 AM, Timothy Arceri wrote:
This pass moves constant outputs to the consuming shader stage
where possible.
V2: limit pass to scalars for now
---
V2 doesn't change any shader-db/vkpipeline-db results as all 32bit
varyings that we don't skip are already scalar. V2 just avoids a
potential bug with doubles as we don't currently split those in
nir_lower_io_to_scalar_early().
src/compiler/nir/nir.h | 2 +
src/compiler/nir/nir_linking_helpers.c | 110 ++++++++++++++++++++++
src/mesa/state_tracker/st_glsl_to_nir.cpp | 2 +-
3 files changed, 113 insertions(+), 1 deletion(-)
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index a0ae9a4430e..0b8c8578953 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2800,6 +2800,8 @@ bool nir_remove_unused_io_vars(nir_shader *shader, struct
exec_list *var_list,
void nir_compact_varyings(nir_shader *producer, nir_shader *consumer,
bool default_to_smooth_interp);
void nir_link_xfb_varyings(nir_shader *producer, nir_shader *consumer);
+bool nir_move_out_const_to_consumer(nir_shader *producer,
+ nir_shader *consumer);
typedef enum {
/* If set, this forces all non-flat fragment shader inputs to be
diff --git a/src/compiler/nir/nir_linking_helpers.c
b/src/compiler/nir/nir_linking_helpers.c
index de6f2481def..a03c327a12f 100644
--- a/src/compiler/nir/nir_linking_helpers.c
+++ b/src/compiler/nir/nir_linking_helpers.c
@@ -22,6 +22,7 @@
*/
#include "nir.h"
+#include "nir_builder.h"
#include "util/set.h"
#include "util/hash_table.h"
@@ -556,3 +557,112 @@ nir_link_xfb_varyings(nir_shader *producer, nir_shader *consumer)
}
}
}
+
+static bool
+try_replace_constant_input(nir_shader *shader,
+ nir_intrinsic_instr *store_intr)
+{
+ nir_variable *out_var =
+ nir_deref_instr_get_variable(nir_src_as_deref(store_intr->src[0]));
+
+ if (out_var->data.mode != nir_var_shader_out)
+ return false;
+
+ /* Skip types that require more complex handling.
+ * TODO: add support for these types.
+ */
+ if (glsl_type_is_array(out_var->type) ||
+ glsl_type_is_dual_slot(out_var->type) ||
+ glsl_type_is_matrix(out_var->type) ||
+ glsl_type_is_struct(out_var->type))
+ return false;
+
+ /* Limit this pass to scalars for now to keep things simple. Most varyings
+ * should have been lowered to scalars at this point anyway.
+ */
+ if (store_intr->num_components != 1)
+ return false;
+
+ if (out_var->data.location < VARYING_SLOT_VAR0 ||
+ out_var->data.location - VARYING_SLOT_VAR0 >= MAX_VARYING)
+ return false;
+
+ nir_function_impl *impl = nir_shader_get_entrypoint(shader);
+
+ nir_builder b;
+ nir_builder_init(&b, impl);
+
+ bool progress = false;
+ nir_foreach_block(block, impl) {
+ nir_foreach_instr(instr, block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+ if (intr->intrinsic != nir_intrinsic_load_deref)
+ continue;
+
+ nir_variable *in_var =
+ nir_deref_instr_get_variable(nir_src_as_deref(intr->src[0]));
+
+ if (in_var->data.mode != nir_var_shader_in)
+ continue;
+
+ if (in_var->data.location != out_var->data.location ||
+ in_var->data.location_frac != out_var->data.location_frac)
+ continue;
+
+ b.cursor = nir_before_instr(instr);
+
+ nir_load_const_instr *out_const =
+ nir_instr_as_load_const(store_intr->src[1].ssa->parent_instr);
+
+ /* Add new const to replace the input */
+ nir_ssa_def *nconst = nir_build_imm(&b, store_intr->num_components,
+ intr->dest.ssa.bit_size,
+ out_const->value);
+
+ nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(nconst));
+
+ progress = true;
+ }
+ }
+
+ return progress;
+}
+
+bool
+nir_move_out_const_to_consumer(nir_shader *producer, nir_shader *consumer)
+{
+ /* TODO: Add support for more shader stage combinations */
+ if (consumer->info.stage != MESA_SHADER_FRAGMENT ||
+ (producer->info.stage != MESA_SHADER_VERTEX &&
+ producer->info.stage != MESA_SHADER_TESS_EVAL))
+ return false;
I would suggest to only enable it for VS->FS for now because I think
it's the most important point, also because it might be trickier for
other stages.
+
+ bool progress = false;
+
+ nir_function_impl *impl = nir_shader_get_entrypoint(producer);
+
+ /* If we find a store in the last block of the producer we can be sure this
+ * is the only possible value for this output.
+ */
+ nir_block *last_block = nir_impl_last_block(impl);
+ nir_foreach_instr_reverse(instr, last_block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+
+ if (intr->intrinsic != nir_intrinsic_store_deref)
+ continue;
+
+ if (intr->src[1].ssa->parent_instr->type != nir_instr_type_load_const) {
+ continue;
+ }
useless braces.
+
+ progress |= try_replace_constant_input(consumer, intr);
+ }
+
+ return progress;
+}
diff --git a/src/mesa/state_tracker/st_glsl_to_nir.cpp
b/src/mesa/state_tracker/st_glsl_to_nir.cpp
index dcf8c2b638e..9141acbc4df 100644
--- a/src/mesa/state_tracker/st_glsl_to_nir.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_nir.cpp
@@ -757,7 +757,7 @@ st_link_nir(struct gl_context *ctx,
*/
if (!prev_shader->sh.LinkedTransformFeedback)
nir_compact_varyings(shader_program->_LinkedShaders[prev]->Program->nir,
- nir, ctx->API != API_OPENGL_COMPAT);
+ nir, ctx->API != API_OPENGL_COMPAT);
}
prev = i;
}
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