[Mesa-dev] [RFC 2/3] nir: Add a pass to rewrite uses of vecN sources to the vecN destination
Jason Ekstrand
jason at jlekstrand.net
Tue Sep 8 17:35:13 PDT 2015
---
src/glsl/Makefile.sources | 1 +
src/glsl/nir/nir.h | 1 +
src/glsl/nir/nir_move_vec_src_uses_to_dest.c | 190 +++++++++++++++++++++++++++
3 files changed, 192 insertions(+)
create mode 100644 src/glsl/nir/nir_move_vec_src_uses_to_dest.c
diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
index c422303..f1b62d8 100644
--- a/src/glsl/Makefile.sources
+++ b/src/glsl/Makefile.sources
@@ -49,6 +49,7 @@ NIR_FILES = \
nir/nir_lower_var_copies.c \
nir/nir_lower_vec_to_movs.c \
nir/nir_metadata.c \
+ nir/nir_move_vec_src_uses_to_dest.c \
nir/nir_normalize_cubemap_coords.c \
nir/nir_opt_constant_folding.c \
nir/nir_opt_copy_propagate.c \
diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
index e7e1881..43c0761 100644
--- a/src/glsl/nir/nir.h
+++ b/src/glsl/nir/nir.h
@@ -1789,6 +1789,7 @@ void nir_lower_vars_to_ssa(nir_shader *shader);
void nir_remove_dead_variables(nir_shader *shader);
+void nir_move_vec_src_uses_to_dest(nir_shader *shader);
void nir_lower_vec_to_movs(nir_shader *shader);
void nir_lower_alu_to_scalar(nir_shader *shader);
void nir_lower_load_const_to_scalar(nir_shader *shader);
diff --git a/src/glsl/nir/nir_move_vec_src_uses_to_dest.c b/src/glsl/nir/nir_move_vec_src_uses_to_dest.c
new file mode 100644
index 0000000..9ac01ef
--- /dev/null
+++ b/src/glsl/nir/nir_move_vec_src_uses_to_dest.c
@@ -0,0 +1,190 @@
+/*
+ * Copyright © 2014 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Authors:
+ * Jason Ekstrand (jason at jlekstrand.net)
+ *
+ */
+
+#include "nir.h"
+
+/*
+ * Implements a pass that tries to move uses vecN sources to their
+ * destinations. This is kind of like an inverse copy-propagation pass.
+ * For instance, if you have
+ *
+ * ssa_1 = vec4(a, b, c, d)
+ * ssa_2 = fadd(a, b)
+ *
+ * This will be turned into
+ *
+ * ssa_1 = vec4(a, b, c, d)
+ * ssa_2 = fadd(ssa_1.x, ssa_1.y)
+ *
+ * While this is "worse" because it adds a bunch of unneeded dependencies, it
+ * actually makes it much easier for vec4-based backends to coalesce the MOV's
+ * that result from the vec4 operation because it doesn't have to worry about
+ * quite as many reads.
+ */
+
+/* Returns true if the given SSA def dominates the instruction. An SSA def is
+ * considered to *not* dominate the instruction that defines it.
+ */
+static bool
+ssa_def_dominates_instr(nir_ssa_def *def, nir_instr *instr)
+{
+ if (instr->index <= def->parent_instr->index) {
+ return false;
+ } else if (def->parent_instr->block == instr->block) {
+ return def->parent_instr->index < instr->index;
+ } else {
+ return nir_block_dominates(def->parent_instr->block, instr->block);
+ }
+}
+
+static bool
+move_vec_src_uses_to_dest_block(nir_block *block, void *shader)
+{
+ nir_foreach_instr(block, instr) {
+ if (instr->type != nir_instr_type_alu)
+ continue;
+
+ nir_alu_instr *vec = nir_instr_as_alu(instr);
+
+ switch (vec->op) {
+ case nir_op_vec2:
+ case nir_op_vec3:
+ case nir_op_vec4:
+ break;
+ default:
+ continue; /* The loop */
+ }
+
+ /* Can't handle saturation */
+ if (vec->dest.saturate)
+ continue;
+
+ assert(vec->dest.dest.is_ssa);
+
+ /* First, mark all of the sources we are going to consider for rewriting
+ * to the destination
+ */
+ int srcs_remaining = 0;
+ for (unsigned i = 0; i < nir_op_infos[vec->op].num_inputs; i++) {
+ /* We can't rewrite a source if it has modifiers */
+ if (vec->src[i].abs || vec->src[i].negate)
+ continue;
+
+ srcs_remaining |= 1 << i;
+ }
+
+ for (unsigned i; i = ffs(srcs_remaining) - 1, srcs_remaining;) {
+ assert(vec->src[i].src.is_ssa);
+
+ int8_t swizzle[4] = { -1, -1, -1, -1 };
+
+ for (unsigned j = i; j < nir_op_infos[vec->op].num_inputs; j++) {
+ if (vec->src[j].src.ssa != vec->src[i].src.ssa)
+ continue;
+
+ /* Mark the given chanle as having been handled */
+ srcs_remaining &= ~(1 << j);
+
+ /* Mark the appropreate channel as coming from src j */
+ swizzle[vec->src[j].swizzle[0]] = j;
+ }
+
+ nir_foreach_use_safe(vec->src[i].src.ssa, use) {
+ if (use->parent_instr == &vec->instr)
+ continue;
+
+ /* We need to dominate the use if we are going to rewrite it */
+ if (!ssa_def_dominates_instr(&vec->dest.dest.ssa, use->parent_instr))
+ continue;
+
+ /* For now, we'll just rewrite ALU instructions */
+ if (use->parent_instr->type != nir_instr_type_alu)
+ continue;
+
+ assert(use->is_ssa);
+
+ nir_alu_instr *use_alu = nir_instr_as_alu(use->parent_instr);
+
+ /* Figure out which source we're actually looking at */
+ nir_alu_src *use_alu_src = exec_node_data(nir_alu_src, use, src);
+ unsigned src_idx = use_alu_src - use_alu->src;
+ assert(src_idx < nir_op_infos[use_alu->op].num_inputs);
+
+ bool can_reswizzle = true;
+ for (unsigned j = 0; j < 4; j++) {
+ if (!nir_alu_instr_channel_used(use_alu, src_idx, j))
+ continue;
+
+ if (swizzle[use_alu_src->swizzle[j]] == -1) {
+ can_reswizzle = false;
+ break;
+ }
+ }
+
+ if (!can_reswizzle)
+ continue;
+
+ /* At this point, we have determined that the given use can be
+ * reswizzled to actually use the destination of the vecN operation.
+ * Go ahead and rewrite it as needed.
+ */
+ nir_instr_rewrite_src(use->parent_instr, use,
+ nir_src_for_ssa(&vec->dest.dest.ssa));
+ for (unsigned j = 0; j < 4; j++) {
+ if (!nir_alu_instr_channel_used(use_alu, src_idx, j))
+ continue;
+
+ use_alu_src->swizzle[j] = swizzle[use_alu_src->swizzle[j]];
+ }
+ }
+ }
+ }
+
+ return true;
+}
+
+static void
+nir_move_vec_src_uses_to_dest_impl(nir_shader *shader, nir_function_impl *impl)
+{
+ nir_metadata_require(impl, nir_metadata_dominance);
+
+ nir_index_instrs(impl);
+ nir_foreach_block(impl, move_vec_src_uses_to_dest_block, shader);
+
+ nir_metadata_preserve(impl, nir_metadata_block_index |
+ nir_metadata_dominance);
+}
+
+void
+nir_move_vec_src_uses_to_dest(nir_shader *shader)
+{
+ nir_foreach_overload(shader, overload) {
+ if (overload->impl)
+ nir_move_vec_src_uses_to_dest_impl(shader, overload->impl);
+ }
+}
+
--
2.5.0.400.gff86faf
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