mirror of
https://github.com/KhronosGroup/SPIRV-Tools
synced 2024-11-22 19:50:05 +00:00
326 lines
10 KiB
C++
326 lines
10 KiB
C++
// Copyright (c) 2019 Google LLC
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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 "code_sink.h"
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#include <vector>
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#include "source/opt/instruction.h"
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#include "source/opt/ir_context.h"
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#include "source/util/bit_vector.h"
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namespace spvtools {
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namespace opt {
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Pass::Status CodeSinkingPass::Process() {
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bool modified = false;
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for (Function& function : *get_module()) {
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cfg()->ForEachBlockInPostOrder(function.entry().get(),
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[&modified, this](BasicBlock* bb) {
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if (SinkInstructionsInBB(bb)) {
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modified = true;
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}
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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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bool CodeSinkingPass::SinkInstructionsInBB(BasicBlock* bb) {
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bool modified = false;
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for (auto inst = bb->rbegin(); inst != bb->rend(); ++inst) {
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if (SinkInstruction(&*inst)) {
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inst = bb->rbegin();
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modified = true;
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}
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}
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return modified;
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}
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bool CodeSinkingPass::SinkInstruction(Instruction* inst) {
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if (inst->opcode() != spv::Op::OpLoad &&
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inst->opcode() != spv::Op::OpAccessChain) {
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return false;
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}
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if (ReferencesMutableMemory(inst)) {
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return false;
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}
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if (BasicBlock* target_bb = FindNewBasicBlockFor(inst)) {
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Instruction* pos = &*target_bb->begin();
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while (pos->opcode() == spv::Op::OpPhi) {
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pos = pos->NextNode();
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}
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inst->InsertBefore(pos);
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context()->set_instr_block(inst, target_bb);
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return true;
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}
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return false;
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}
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BasicBlock* CodeSinkingPass::FindNewBasicBlockFor(Instruction* inst) {
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assert(inst->result_id() != 0 && "Instruction should have a result.");
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BasicBlock* original_bb = context()->get_instr_block(inst);
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BasicBlock* bb = original_bb;
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std::unordered_set<uint32_t> bbs_with_uses;
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get_def_use_mgr()->ForEachUse(
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inst, [&bbs_with_uses, this](Instruction* use, uint32_t idx) {
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if (use->opcode() != spv::Op::OpPhi) {
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BasicBlock* use_bb = context()->get_instr_block(use);
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if (use_bb) {
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bbs_with_uses.insert(use_bb->id());
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}
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} else {
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bbs_with_uses.insert(use->GetSingleWordOperand(idx + 1));
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}
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});
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while (true) {
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// If |inst| is used in |bb|, then |inst| cannot be moved any further.
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if (bbs_with_uses.count(bb->id())) {
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break;
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}
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// If |bb| has one successor (succ_bb), and |bb| is the only predecessor
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// of succ_bb, then |inst| can be moved to succ_bb. If succ_bb, has move
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// then one predecessor, then moving |inst| into succ_bb could cause it to
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// be executed more often, so the search has to stop.
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if (bb->terminator()->opcode() == spv::Op::OpBranch) {
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uint32_t succ_bb_id = bb->terminator()->GetSingleWordInOperand(0);
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if (cfg()->preds(succ_bb_id).size() == 1) {
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bb = context()->get_instr_block(succ_bb_id);
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continue;
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} else {
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break;
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}
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}
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// The remaining checks need to know the merge node. If there is no merge
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// instruction or an OpLoopMerge, then it is a break or continue. We could
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// figure it out, but not worth doing it now.
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Instruction* merge_inst = bb->GetMergeInst();
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if (merge_inst == nullptr ||
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merge_inst->opcode() != spv::Op::OpSelectionMerge) {
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break;
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}
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// Check all of the successors of |bb| it see which lead to a use of |inst|
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// before reaching the merge node.
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bool used_in_multiple_blocks = false;
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uint32_t bb_used_in = 0;
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bb->ForEachSuccessorLabel([this, bb, &bb_used_in, &used_in_multiple_blocks,
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&bbs_with_uses](uint32_t* succ_bb_id) {
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if (IntersectsPath(*succ_bb_id, bb->MergeBlockIdIfAny(), bbs_with_uses)) {
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if (bb_used_in == 0) {
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bb_used_in = *succ_bb_id;
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} else {
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used_in_multiple_blocks = true;
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}
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}
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});
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// If more than one successor, which is not the merge block, uses |inst|
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// then we have to leave |inst| in bb because there is none of the
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// successors dominate all uses of |inst|.
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if (used_in_multiple_blocks) {
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break;
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}
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if (bb_used_in == 0) {
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// If |inst| is not used before reaching the merge node, then we can move
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// |inst| to the merge node.
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bb = context()->get_instr_block(bb->MergeBlockIdIfAny());
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} else {
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// If the only successor that leads to a used of |inst| has more than 1
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// predecessor, then moving |inst| could cause it to be executed more
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// often, so we cannot move it.
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if (cfg()->preds(bb_used_in).size() != 1) {
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break;
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}
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// If |inst| is used after the merge block, then |bb_used_in| does not
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// dominate all of the uses. So we cannot move |inst| any further.
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if (IntersectsPath(bb->MergeBlockIdIfAny(), original_bb->id(),
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bbs_with_uses)) {
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break;
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}
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// Otherwise, |bb_used_in| dominates all uses, so move |inst| into that
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// block.
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bb = context()->get_instr_block(bb_used_in);
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}
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continue;
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}
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return (bb != original_bb ? bb : nullptr);
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}
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bool CodeSinkingPass::ReferencesMutableMemory(Instruction* inst) {
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if (!inst->IsLoad()) {
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return false;
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}
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Instruction* base_ptr = inst->GetBaseAddress();
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if (base_ptr->opcode() != spv::Op::OpVariable) {
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return true;
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}
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if (base_ptr->IsReadOnlyPointer()) {
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return false;
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}
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if (HasUniformMemorySync()) {
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return true;
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}
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if (spv::StorageClass(base_ptr->GetSingleWordInOperand(0)) !=
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spv::StorageClass::Uniform) {
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return true;
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}
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return HasPossibleStore(base_ptr);
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}
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bool CodeSinkingPass::HasUniformMemorySync() {
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if (checked_for_uniform_sync_) {
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return has_uniform_sync_;
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}
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bool has_sync = false;
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get_module()->ForEachInst([this, &has_sync](Instruction* inst) {
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switch (inst->opcode()) {
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case spv::Op::OpMemoryBarrier: {
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uint32_t mem_semantics_id = inst->GetSingleWordInOperand(1);
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if (IsSyncOnUniform(mem_semantics_id)) {
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has_sync = true;
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}
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break;
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}
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case spv::Op::OpControlBarrier:
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case spv::Op::OpAtomicLoad:
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case spv::Op::OpAtomicStore:
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case spv::Op::OpAtomicExchange:
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case spv::Op::OpAtomicIIncrement:
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case spv::Op::OpAtomicIDecrement:
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case spv::Op::OpAtomicIAdd:
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case spv::Op::OpAtomicFAddEXT:
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case spv::Op::OpAtomicISub:
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case spv::Op::OpAtomicSMin:
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case spv::Op::OpAtomicUMin:
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case spv::Op::OpAtomicFMinEXT:
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case spv::Op::OpAtomicSMax:
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case spv::Op::OpAtomicUMax:
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case spv::Op::OpAtomicFMaxEXT:
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case spv::Op::OpAtomicAnd:
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case spv::Op::OpAtomicOr:
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case spv::Op::OpAtomicXor:
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case spv::Op::OpAtomicFlagTestAndSet:
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case spv::Op::OpAtomicFlagClear: {
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uint32_t mem_semantics_id = inst->GetSingleWordInOperand(2);
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if (IsSyncOnUniform(mem_semantics_id)) {
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has_sync = true;
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}
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break;
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}
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case spv::Op::OpAtomicCompareExchange:
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case spv::Op::OpAtomicCompareExchangeWeak:
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if (IsSyncOnUniform(inst->GetSingleWordInOperand(2)) ||
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IsSyncOnUniform(inst->GetSingleWordInOperand(3))) {
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has_sync = true;
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}
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break;
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default:
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break;
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}
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});
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has_uniform_sync_ = has_sync;
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return has_sync;
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}
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bool CodeSinkingPass::IsSyncOnUniform(uint32_t mem_semantics_id) const {
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const analysis::Constant* mem_semantics_const =
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context()->get_constant_mgr()->FindDeclaredConstant(mem_semantics_id);
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assert(mem_semantics_const != nullptr &&
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"Expecting memory semantics id to be a constant.");
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assert(mem_semantics_const->AsIntConstant() &&
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"Memory semantics should be an integer.");
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uint32_t mem_semantics_int = mem_semantics_const->GetU32();
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// If it does not affect uniform memory, then it is does not apply to uniform
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// memory.
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if ((mem_semantics_int & uint32_t(spv::MemorySemanticsMask::UniformMemory)) ==
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0) {
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return false;
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}
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// Check if there is an acquire or release. If so not, this it does not add
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// any memory constraints.
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return (mem_semantics_int &
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uint32_t(spv::MemorySemanticsMask::Acquire |
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spv::MemorySemanticsMask::AcquireRelease |
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spv::MemorySemanticsMask::Release)) != 0;
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}
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bool CodeSinkingPass::HasPossibleStore(Instruction* var_inst) {
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assert(var_inst->opcode() == spv::Op::OpVariable ||
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var_inst->opcode() == spv::Op::OpAccessChain ||
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var_inst->opcode() == spv::Op::OpPtrAccessChain);
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return get_def_use_mgr()->WhileEachUser(var_inst, [this](Instruction* use) {
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switch (use->opcode()) {
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case spv::Op::OpStore:
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return true;
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case spv::Op::OpAccessChain:
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case spv::Op::OpPtrAccessChain:
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return HasPossibleStore(use);
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default:
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return false;
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}
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});
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}
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bool CodeSinkingPass::IntersectsPath(uint32_t start, uint32_t end,
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const std::unordered_set<uint32_t>& set) {
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std::vector<uint32_t> worklist;
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worklist.push_back(start);
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std::unordered_set<uint32_t> already_done;
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already_done.insert(start);
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while (!worklist.empty()) {
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BasicBlock* bb = context()->get_instr_block(worklist.back());
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worklist.pop_back();
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if (bb->id() == end) {
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continue;
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}
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if (set.count(bb->id())) {
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return true;
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}
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bb->ForEachSuccessorLabel([&already_done, &worklist](uint32_t* succ_bb_id) {
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if (already_done.insert(*succ_bb_id).second) {
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worklist.push_back(*succ_bb_id);
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}
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});
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}
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return false;
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}
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// namespace opt
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} // namespace opt
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} // namespace spvtools
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