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https://github.com/KhronosGroup/SPIRV-Tools
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4ba9dcc8a0
This implements the conditional constant propagation pass proposed in Constant propagation with conditional branches, Wegman and Zadeck, ACM TOPLAS 13(2):181-210. The main logic resides in CCPPass::VisitInstruction. Instruction that may produce a constant value are evaluated with the constant folder. If they produce a new constant, the instruction is considered interesting. Otherwise, it's considered varying (for unfoldable instructions) or just not interesting (when not enough operands have a constant value). The other main piece of logic is in CCPPass::VisitBranch. This evaluates the selector of the branch. When it's found to be a known value, it computes the destination basic block and sets it. This tells the propagator which branches to follow. The patch required extensions to the constant manager as well. Instead of hashing the Constant pointers, this patch changes the constant pool to hash the contents of the Constant. This allows the lookups to be done using the actual values of the Constant, preventing duplicate definitions.
40 lines
1.1 KiB
C++
40 lines
1.1 KiB
C++
// Copyright (c) 2017 Google Inc.
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//
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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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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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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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#ifndef LIBSPIRV_UTIL_FOLD_H_
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#define LIBSPIRV_UTIL_FOLD_H_
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#include "constants.h"
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#include "def_use_manager.h"
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#include <cstdint>
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#include <vector>
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namespace spvtools {
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namespace opt {
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uint32_t FoldScalars(SpvOp opcode,
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const std::vector<const analysis::Constant*>& operands);
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std::vector<uint32_t> FoldVectors(
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SpvOp opcode, uint32_t num_dims,
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const std::vector<const analysis::Constant*>& operands);
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bool IsFoldableOpcode(SpvOp opcode);
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} // namespace opt
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} // namespace spvtools
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#endif // LIBSPIRV_UTIL_FOLD_H_
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