nir: Skip emitting no-op movs from the builder.
Having passes generate these is just making more work for copy propagation (and thus probably calling more optimization passes) later. Noticed while trying to debug nir_opt_algebraic() top-to-bottom having O(n^2) behavior due to not finding new matches in replacement code. Reviewed-by: Ian Romanick <ian.d.romainck@intel.com> Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
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@ -458,6 +458,16 @@ static inline nir_ssa_def *
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nir_mov_alu(nir_builder *build, nir_alu_src src, unsigned num_components)
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{
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assert(!src.abs && !src.negate);
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if (src.src.is_ssa && src.src.ssa->num_components == num_components) {
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bool any_swizzles = false;
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for (unsigned i = 0; i < num_components; i++) {
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if (src.swizzle[i] != i)
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any_swizzles = true;
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}
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if (!any_swizzles)
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return src.src.ssa;
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}
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nir_alu_instr *mov = nir_alu_instr_create(build->shader, nir_op_mov);
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nir_ssa_dest_init(&mov->instr, &mov->dest.dest, num_components,
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nir_src_bit_size(src.src), NULL);
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@ -673,9 +673,8 @@ nir_replace_instr(nir_builder *build, nir_alu_instr *instr,
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instr->dest.dest.ssa.bit_size,
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&state, &instr->instr);
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/* Inserting a mov may be unnecessary. However, it's much easier to
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* simply let copy propagation clean this up than to try to go through
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* and rewrite swizzles ourselves.
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/* Note that NIR builder will elide the MOV if it's a no-op, which may
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* allow more work to be done in a single pass through algebraic.
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*/
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nir_ssa_def *ssa_val =
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nir_mov_alu(build, val, instr->dest.dest.ssa.num_components);
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