81 lines
2.4 KiB
C++
81 lines
2.4 KiB
C++
/* Copyright 2022 The OpenXLA Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==============================================================================*/
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#ifndef XLA_SERVICE_REDUCE_DECOMPOSER_H_
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#define XLA_SERVICE_REDUCE_DECOMPOSER_H_
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#include <functional>
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#include "xla/service/hlo_pass_interface.h"
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namespace xla {
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// For each reduction R(I), ensures the postcondition:
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//
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// !custom_layout_allowed(R)
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// =>
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// layout(R) == layout(I) # modulo removed dimensions
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//
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// To achieve that, decomposes layout-mutating reductions which do not satisfy
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// `custom_layout_allowed` into a reduction and a copy.
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//
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// For a singular reduction:
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//
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// -> reduce ->
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//
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// Gets turned into:
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//
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// -> reduce -> copy ->
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//
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// For a variadic recuction, the layout assignment guarantees that the layout
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// is the same for all outputs. This pass will transpose the variadic reduction
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// inputs which have different physical layout to the first operand.
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//
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// A{L} \
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// B{L} -> reduce{L'} ->
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// C{L} /
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//
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// Get turned into:
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//
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// A{L} \ / GTE(1) -> copy{L'} \
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// B{L} -> reduce{E(L)} --- GTE(2) -> copy{L'} - Tuple{L'}
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// C{L} / \ GTE(3) -> copy{L'} /
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//
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// Where E(L) is expected layout of a reduction (original layout with reduce
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// dimensions dropped).
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//
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// PRECONDITION:
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// In variadic reduction, all outputs have the same layout
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// (enforced by layout assignment).
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class ReduceDecomposer : public HloModulePass {
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public:
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explicit ReduceDecomposer(HloPredicate custom_layout_allowed = nullptr)
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: custom_layout_allowed_(custom_layout_allowed) {}
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absl::string_view name() const override { return "reduce-decomposer"; }
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using HloPassInterface::Run;
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StatusOr<bool> Run(
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HloModule* module,
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const absl::flat_hash_set<absl::string_view>& execution_threads) override;
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private:
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HloPredicate custom_layout_allowed_;
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};
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} // namespace xla
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#endif // XLA_SERVICE_REDUCE_DECOMPOSER_H_
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