nir: Add a memcpy optimization pass
This pass attempts to optimize three broad categories of memcpy: 1. Self-copies: These we can discard out-of-hand. 2. Vector copies: It doesn't matter what the vector size is or if the source and destination have different vector types, it's still easy enough to emit a load/store pair. 3. Tightly packed copies: In the case where a type is tightly packed (no padding bits), we can replace the memcpy with a copy_deref instruction which the optimizer is far better at handling. This has proven capable of getting rid of many of the memcpy instances in some rather gnarly OpenCL C kernels I've been looking at, even after coming out of LLVM's optimizer. Reviewed-by: Jesse Natalie <jenatali@microsoft.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6871>
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@ -329,6 +329,7 @@ NIR_FILES = \
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nir/nir_opt_loop_unroll.c \
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nir/nir_opt_large_constants.c \
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nir/nir_opt_load_store_vectorize.c \
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nir/nir_opt_memcpy.c \
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nir/nir_opt_move.c \
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nir/nir_opt_peephole_select.c \
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nir/nir_opt_rematerialize_compares.c \
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@ -210,6 +210,7 @@ files_libnir = files(
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'nir_opt_large_constants.c',
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'nir_opt_load_store_vectorize.c',
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'nir_opt_loop_unroll.c',
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'nir_opt_memcpy.c',
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'nir_opt_move.c',
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'nir_opt_peephole_select.c',
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'nir_opt_rematerialize_compares.c',
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@ -4126,6 +4126,7 @@ void nir_lower_deref_copy_instr(struct nir_builder *b,
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nir_intrinsic_instr *copy);
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bool nir_lower_var_copies(nir_shader *shader);
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bool nir_opt_memcpy(nir_shader *shader);
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bool nir_lower_memcpy(nir_shader *shader);
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void nir_fixup_deref_modes(nir_shader *shader);
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@ -0,0 +1,224 @@
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/*
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* Copyright © 2020 Intel Corporation
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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#include "nir_builder.h"
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static bool
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opt_memcpy_deref_cast(nir_intrinsic_instr *cpy, nir_src *deref_src)
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{
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assert(cpy->intrinsic == nir_intrinsic_memcpy_deref);
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nir_deref_instr *cast = nir_src_as_deref(*deref_src);
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if (cast == NULL || cast->deref_type != nir_deref_type_cast)
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return false;
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/* We always have to replace the source with a deref, not a bare uint
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* pointer. If it's the first deref in the chain, bail.
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*/
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nir_deref_instr *parent = nir_src_as_deref(cast->parent);
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if (parent == NULL)
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return false;
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/* If it has useful alignment information, we want to keep that */
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if (cast->cast.align_mul > 0)
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return false;
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/* Casts to uint8 or int8 never do us any good; get rid of them */
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if (cast->type == glsl_int8_t_type() ||
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cast->type == glsl_uint8_t_type()) {
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nir_instr_rewrite_src(&cpy->instr, deref_src,
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nir_src_for_ssa(&parent->dest.ssa));
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return true;
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}
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int64_t parent_type_size = glsl_get_explicit_size(parent->type, false);
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if (parent_type_size < 0)
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return false;
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if (!nir_src_is_const(cpy->src[2]))
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return false;
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/* We don't want to get rid of the cast if the resulting type would be
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* smaller than the amount of data we're copying.
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*/
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if (nir_src_as_uint(cpy->src[2]) < (uint64_t)parent_type_size)
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return false;
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nir_instr_rewrite_src(&cpy->instr, deref_src,
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nir_src_for_ssa(&parent->dest.ssa));
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return true;
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}
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static bool
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type_is_tightly_packed(const struct glsl_type *type, unsigned *size_out)
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{
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unsigned size = 0;
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if (glsl_type_is_struct_or_ifc(type)) {
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unsigned num_fields = glsl_get_length(type);
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for (unsigned i = 0; i < num_fields; i++) {
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const struct glsl_struct_field *field =
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glsl_get_struct_field_data(type, i);
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if (field->offset < 0 || field->offset != size)
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return false;
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unsigned field_size;
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if (!type_is_tightly_packed(field->type, &field_size))
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return false;
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size = field->offset + field_size;
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}
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} else if (glsl_type_is_array_or_matrix(type)) {
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if (glsl_type_is_unsized_array(type))
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return false;
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unsigned stride = glsl_get_explicit_stride(type);
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if (stride == 0)
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return false;
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const struct glsl_type *elem_type = glsl_get_array_element(type);
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unsigned elem_size;
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if (!type_is_tightly_packed(elem_type, &elem_size))
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return false;
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if (elem_size != stride)
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return false;
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size = stride * glsl_get_length(type);
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} else {
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assert(glsl_type_is_vector_or_scalar(type));
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if (glsl_get_explicit_stride(type) > 0)
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return false;
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if (glsl_type_is_boolean(type))
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return false;
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size = glsl_get_explicit_size(type, false);
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}
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if (size_out)
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*size_out = size;
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return true;
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}
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static bool
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try_lower_memcpy(nir_builder *b, nir_intrinsic_instr *cpy)
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{
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nir_deref_instr *dst = nir_src_as_deref(cpy->src[0]);
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nir_deref_instr *src = nir_src_as_deref(cpy->src[1]);
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/* A self-copy can always be eliminated */
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if (dst == src) {
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nir_instr_remove(&cpy->instr);
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return true;
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}
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if (!nir_src_is_const(cpy->src[2]))
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return false;
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uint64_t size = nir_src_as_uint(cpy->src[2]);
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if (size == 0) {
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nir_instr_remove(&cpy->instr);
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return true;
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}
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if (glsl_type_is_vector_or_scalar(src->type) &&
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glsl_type_is_vector_or_scalar(dst->type) &&
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glsl_get_explicit_size(dst->type, false) == size &&
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glsl_get_explicit_size(src->type, false) == size) {
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b->cursor = nir_instr_remove(&cpy->instr);
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nir_ssa_def *data =
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nir_load_deref_with_access(b, src, nir_intrinsic_src_access(cpy));
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data = nir_bitcast_vector(b, data, glsl_get_bit_size(dst->type));
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assert(data->num_components == glsl_get_vector_elements(dst->type));
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nir_store_deref_with_access(b, src, data, ~0 /* write mask */,
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nir_intrinsic_dst_access(cpy));
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return true;
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}
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unsigned type_size;
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if (dst->type == src->type &&
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type_is_tightly_packed(dst->type, &type_size) &&
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type_size == size) {
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b->cursor = nir_instr_remove(&cpy->instr);
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nir_copy_deref_with_access(b, dst, src,
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nir_intrinsic_dst_access(cpy),
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nir_intrinsic_src_access(cpy));
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return true;
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}
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return false;
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}
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static bool
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opt_memcpy_impl(nir_function_impl *impl)
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{
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bool progress = false;
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nir_builder b;
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nir_builder_init(&b, impl);
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nir_foreach_block(block, impl) {
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nir_foreach_instr_safe(instr, block) {
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if (instr->type != nir_instr_type_intrinsic)
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continue;
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nir_intrinsic_instr *cpy = nir_instr_as_intrinsic(instr);
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if (cpy->intrinsic != nir_intrinsic_memcpy_deref)
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continue;
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while (opt_memcpy_deref_cast(cpy, &cpy->src[0]))
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progress = true;
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while (opt_memcpy_deref_cast(cpy, &cpy->src[1]))
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progress = true;
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if (try_lower_memcpy(&b, cpy)) {
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progress = true;
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continue;
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}
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}
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}
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if (progress) {
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nir_metadata_preserve(impl, nir_metadata_block_index |
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nir_metadata_dominance);
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} else {
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nir_metadata_preserve(impl, nir_metadata_all);
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}
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return progress;
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}
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bool
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nir_opt_memcpy(nir_shader *shader)
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{
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bool progress = false;
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nir_foreach_function(function, shader) {
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if (function->impl && opt_memcpy_impl(function->impl))
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progress = true;
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}
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return progress;
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}
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