mirror of
https://github.com/KhronosGroup/SPIRV-Tools
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83228137e1
Re-formatted the source tree with the command:
$ /usr/bin/clang-format -style=file -i \
$(find include source tools test utils -name '*.cpp' -or -name '*.h')
This required a fix to source/val/decoration.h. It was not including
spirv.h, which broke builds when the #include headers were re-ordered by
clang-format.
115 lines
3.9 KiB
C++
115 lines
3.9 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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#include "dead_variable_elimination.h"
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#include "ir_context.h"
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#include "reflect.h"
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namespace spvtools {
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namespace opt {
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// This optimization removes global variables that are not needed because they
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// are definitely not accessed.
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Pass::Status DeadVariableElimination::Process(ir::IRContext* c) {
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// The algorithm will compute the reference count for every global variable.
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// Anything with a reference count of 0 will then be deleted. For variables
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// that might have references that are not explicit in this context, we use
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// the
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// value kMustKeep as the reference count.
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InitializeProcessing(c);
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std::vector<uint32_t> ids_to_remove;
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// Get the reference count for all of the global OpVariable instructions.
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for (auto& inst : context()->types_values()) {
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if (inst.opcode() != SpvOp::SpvOpVariable) {
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continue;
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}
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size_t count = 0;
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uint32_t result_id = inst.result_id();
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// Check the linkage. If it is exported, it could be reference somewhere
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// else, so we must keep the variable around.
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get_decoration_mgr()->ForEachDecoration(
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result_id, SpvDecorationLinkageAttributes,
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[&count](const ir::Instruction& linkage_instruction) {
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uint32_t last_operand = linkage_instruction.NumOperands() - 1;
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if (linkage_instruction.GetSingleWordOperand(last_operand) ==
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SpvLinkageTypeExport) {
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count = kMustKeep;
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}
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});
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if (count != kMustKeep) {
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// If we don't have to keep the instruction for other reasons, then look
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// at the uses and count the number of real references.
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count = 0;
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get_def_use_mgr()->ForEachUser(
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result_id, [&count](ir::Instruction* user) {
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if (!ir::IsAnnotationInst(user->opcode()) &&
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user->opcode() != SpvOpName) {
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++count;
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}
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});
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}
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reference_count_[result_id] = count;
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if (count == 0) {
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ids_to_remove.push_back(result_id);
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}
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}
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// Remove all of the variables that have a reference count of 0.
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bool modified = false;
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if (!ids_to_remove.empty()) {
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modified = true;
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for (auto result_id : ids_to_remove) {
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DeleteVariable(result_id);
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}
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}
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return (modified ? Status::SuccessWithChange : Status::SuccessWithoutChange);
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}
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void DeadVariableElimination::DeleteVariable(uint32_t result_id) {
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ir::Instruction* inst = get_def_use_mgr()->GetDef(result_id);
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assert(inst->opcode() == SpvOpVariable &&
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"Should not be trying to delete anything other than an OpVariable.");
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// Look for an initializer that references another variable. We need to know
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// if that variable can be deleted after the reference is removed.
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if (inst->NumOperands() == 4) {
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ir::Instruction* initializer =
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get_def_use_mgr()->GetDef(inst->GetSingleWordOperand(3));
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// TODO: Handle OpSpecConstantOP which might be defined in terms of other
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// variables. Will probably require a unified dead code pass that does all
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// instruction types. (Issue 906)
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if (initializer->opcode() == SpvOpVariable) {
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uint32_t initializer_id = initializer->result_id();
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size_t& count = reference_count_[initializer_id];
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if (count != kMustKeep) {
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--count;
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}
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if (count == 0) {
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DeleteVariable(initializer_id);
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}
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}
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}
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context()->KillDef(result_id);
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}
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} // namespace opt
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} // namespace spvtools
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