mirror of
https://github.com/KhronosGroup/SPIRV-Tools
synced 2024-11-30 15:00:06 +00:00
1182415581
Currently only SPV_KHR_variable_pointers is disallowed in passes which do pointer analysis. Positive and negative tests of the general extensions mechanism were added to aggressive_dce but cover all passes.
375 lines
13 KiB
C++
375 lines
13 KiB
C++
// Copyright (c) 2017 The Khronos Group Inc.
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// Copyright (c) 2017 Valve Corporation
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// Copyright (c) 2017 LunarG 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_branch_elim_pass.h"
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#include "cfa.h"
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#include "iterator.h"
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namespace spvtools {
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namespace opt {
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namespace {
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const uint32_t kEntryPointFunctionIdInIdx = 1;
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const uint32_t kBranchCondConditionalIdInIdx = 0;
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const uint32_t kBranchCondTrueLabIdInIdx = 1;
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const uint32_t kBranchCondFalseLabIdInIdx = 2;
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const uint32_t kSelectionMergeMergeBlockIdInIdx = 0;
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const uint32_t kPhiVal0IdInIdx = 0;
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const uint32_t kPhiLab0IdInIdx = 1;
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const uint32_t kPhiVal1IdInIdx = 2;
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const uint32_t kLoopMergeMergeBlockIdInIdx = 0;
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const uint32_t kLoopMergeContinueBlockIdInIdx = 1;
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} // anonymous namespace
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uint32_t DeadBranchElimPass::MergeBlockIdIfAny(
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const ir::BasicBlock& blk, uint32_t* cbid) const {
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auto merge_ii = blk.cend();
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--merge_ii;
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uint32_t mbid = 0;
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*cbid = 0;
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if (merge_ii != blk.cbegin()) {
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--merge_ii;
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if (merge_ii->opcode() == SpvOpLoopMerge) {
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mbid = merge_ii->GetSingleWordInOperand(kLoopMergeMergeBlockIdInIdx);
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*cbid = merge_ii->GetSingleWordInOperand(kLoopMergeContinueBlockIdInIdx);
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}
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else if (merge_ii->opcode() == SpvOpSelectionMerge) {
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mbid = merge_ii->GetSingleWordInOperand(
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kSelectionMergeMergeBlockIdInIdx);
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}
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}
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return mbid;
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}
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void DeadBranchElimPass::ComputeStructuredSuccessors(ir::Function* func) {
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// If header, make merge block first successor. If a loop header, make
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// the second successor the continue target.
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for (auto& blk : *func) {
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uint32_t cbid;
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uint32_t mbid = MergeBlockIdIfAny(blk, &cbid);
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if (mbid != 0) {
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block2structured_succs_[&blk].push_back(id2block_[mbid]);
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if (cbid != 0)
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block2structured_succs_[&blk].push_back(id2block_[cbid]);
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}
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// add true successors
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blk.ForEachSuccessorLabel([&blk, this](uint32_t sbid) {
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block2structured_succs_[&blk].push_back(id2block_[sbid]);
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});
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}
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}
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void DeadBranchElimPass::ComputeStructuredOrder(
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ir::Function* func, std::list<ir::BasicBlock*>* order) {
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// Compute structured successors and do DFS
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ComputeStructuredSuccessors(func);
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auto ignore_block = [](cbb_ptr) {};
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auto ignore_edge = [](cbb_ptr, cbb_ptr) {};
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auto get_structured_successors = [this](const ir::BasicBlock* block) {
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return &(block2structured_succs_[block]); };
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// TODO(greg-lunarg): Get rid of const_cast by making moving const
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// out of the cfa.h prototypes and into the invoking code.
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auto post_order = [&](cbb_ptr b) {
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order->push_front(const_cast<ir::BasicBlock*>(b)); };
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spvtools::CFA<ir::BasicBlock>::DepthFirstTraversal(
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&*func->begin(), get_structured_successors, ignore_block, post_order,
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ignore_edge);
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}
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void DeadBranchElimPass::GetConstCondition(
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uint32_t condId, bool* condVal, bool* condIsConst) {
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ir::Instruction* cInst = def_use_mgr_->GetDef(condId);
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switch (cInst->opcode()) {
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case SpvOpConstantFalse: {
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*condVal = false;
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*condIsConst = true;
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} break;
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case SpvOpConstantTrue: {
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*condVal = true;
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*condIsConst = true;
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} break;
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case SpvOpLogicalNot: {
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bool negVal;
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(void)GetConstCondition(cInst->GetSingleWordInOperand(0),
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&negVal, condIsConst);
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if (*condIsConst)
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*condVal = !negVal;
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} break;
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default: {
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*condIsConst = false;
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} break;
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}
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}
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void DeadBranchElimPass::AddBranch(uint32_t labelId, ir::BasicBlock* bp) {
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std::unique_ptr<ir::Instruction> newBranch(
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new ir::Instruction(SpvOpBranch, 0, 0,
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{{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {labelId}}}));
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def_use_mgr_->AnalyzeInstDefUse(&*newBranch);
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bp->AddInstruction(std::move(newBranch));
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}
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void DeadBranchElimPass::AddSelectionMerge(uint32_t labelId,
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ir::BasicBlock* bp) {
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std::unique_ptr<ir::Instruction> newMerge(
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new ir::Instruction(SpvOpSelectionMerge, 0, 0,
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{{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {labelId}},
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{spv_operand_type_t::SPV_OPERAND_TYPE_LITERAL_INTEGER, {0}}}));
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def_use_mgr_->AnalyzeInstDefUse(&*newMerge);
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bp->AddInstruction(std::move(newMerge));
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}
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void DeadBranchElimPass::AddBranchConditional(uint32_t condId,
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uint32_t trueLabId, uint32_t falseLabId, ir::BasicBlock* bp) {
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std::unique_ptr<ir::Instruction> newBranchCond(
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new ir::Instruction(SpvOpBranchConditional, 0, 0,
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{{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {condId}},
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{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {trueLabId}},
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{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {falseLabId}}}));
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def_use_mgr_->AnalyzeInstDefUse(&*newBranchCond);
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bp->AddInstruction(std::move(newBranchCond));
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}
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void DeadBranchElimPass::KillAllInsts(ir::BasicBlock* bp) {
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bp->ForEachInst([this](ir::Instruction* ip) {
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def_use_mgr_->KillInst(ip);
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});
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}
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bool DeadBranchElimPass::GetConstConditionalSelectionBranch(ir::BasicBlock* bp,
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ir::Instruction** branchInst, ir::Instruction** mergeInst,
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uint32_t *condId, bool *condVal) {
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auto ii = bp->end();
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--ii;
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*branchInst = &*ii;
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if ((*branchInst)->opcode() != SpvOpBranchConditional)
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return false;
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if (ii == bp->begin())
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return false;
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--ii;
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*mergeInst = &*ii;
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if ((*mergeInst)->opcode() != SpvOpSelectionMerge)
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return false;
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bool condIsConst;
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*condId = (*branchInst)->GetSingleWordInOperand(
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kBranchCondConditionalIdInIdx);
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(void) GetConstCondition(*condId, condVal, &condIsConst);
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return condIsConst;
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}
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bool DeadBranchElimPass::HasNonPhiRef(uint32_t labelId) {
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analysis::UseList* uses = def_use_mgr_->GetUses(labelId);
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if (uses == nullptr)
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return false;
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for (auto u : *uses)
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if (u.inst->opcode() != SpvOpPhi)
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return true;
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return false;
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}
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bool DeadBranchElimPass::EliminateDeadBranches(ir::Function* func) {
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// Traverse blocks in structured order
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std::list<ir::BasicBlock*> structuredOrder;
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ComputeStructuredOrder(func, &structuredOrder);
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std::unordered_set<ir::BasicBlock*> elimBlocks;
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bool modified = false;
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for (auto bi = structuredOrder.begin(); bi != structuredOrder.end(); ++bi) {
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// Skip blocks that are already in the elimination set
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if (elimBlocks.find(*bi) != elimBlocks.end())
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continue;
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// Skip blocks that don't have constant conditional branch preceded
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// by OpSelectionMerge
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ir::Instruction* br;
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ir::Instruction* mergeInst;
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uint32_t condId;
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bool condVal;
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if (!GetConstConditionalSelectionBranch(*bi, &br, &mergeInst, &condId,
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&condVal))
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continue;
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// Replace conditional branch with unconditional branch
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const uint32_t trueLabId =
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br->GetSingleWordInOperand(kBranchCondTrueLabIdInIdx);
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const uint32_t falseLabId =
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br->GetSingleWordInOperand(kBranchCondFalseLabIdInIdx);
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const uint32_t mergeLabId =
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mergeInst->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx);
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const uint32_t liveLabId = condVal == true ? trueLabId : falseLabId;
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const uint32_t deadLabId = condVal == true ? falseLabId : trueLabId;
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AddBranch(liveLabId, *bi);
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def_use_mgr_->KillInst(br);
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def_use_mgr_->KillInst(mergeInst);
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// Iterate to merge block adding dead blocks to elimination set
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auto dbi = bi;
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++dbi;
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uint32_t dLabId = (*dbi)->id();
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while (dLabId != mergeLabId) {
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if (!HasNonPhiRef(dLabId)) {
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// Kill use/def for all instructions and mark block for elimination
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KillAllInsts(*dbi);
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elimBlocks.insert(*dbi);
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}
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++dbi;
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dLabId = (*dbi)->id();
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}
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// Process phi instructions in merge block.
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// elimBlocks are now blocks which cannot precede merge block. Also,
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// if eliminated branch is to merge label, remember the conditional block
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// also cannot precede merge block.
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uint32_t deadCondLabId = 0;
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if (deadLabId == mergeLabId)
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deadCondLabId = (*bi)->id();
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(*dbi)->ForEachPhiInst([&elimBlocks, &deadCondLabId, this](
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ir::Instruction* phiInst) {
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const uint32_t phiLabId0 =
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phiInst->GetSingleWordInOperand(kPhiLab0IdInIdx);
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const bool useFirst =
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elimBlocks.find(id2block_[phiLabId0]) == elimBlocks.end() &&
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phiLabId0 != deadCondLabId;
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const uint32_t phiValIdx =
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useFirst ? kPhiVal0IdInIdx : kPhiVal1IdInIdx;
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const uint32_t replId = phiInst->GetSingleWordInOperand(phiValIdx);
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const uint32_t phiId = phiInst->result_id();
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(void)def_use_mgr_->ReplaceAllUsesWith(phiId, replId);
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def_use_mgr_->KillInst(phiInst);
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});
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// If merge block has no predecessors, replace the new branch with
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// a MergeSelection/BranchCondition using the original constant condition
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// and the mergeblock as the false branch. This is done so the merge block
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// is not orphaned, which could cause invalid control flow in certain case.
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// TODO(greg-lunarg): Do this only in cases where invalid code is caused.
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if (!HasNonPhiRef(mergeLabId)) {
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auto eii = (*bi)->end();
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--eii;
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ir::Instruction* nbr = &*eii;
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AddSelectionMerge(mergeLabId, *bi);
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if (condVal == true)
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AddBranchConditional(condId, liveLabId, mergeLabId, *bi);
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else
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AddBranchConditional(condId, mergeLabId, liveLabId, *bi);
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def_use_mgr_->KillInst(nbr);
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}
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modified = true;
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}
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// Erase dead blocks
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for (auto ebi = func->begin(); ebi != func->end(); )
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if (elimBlocks.find(&*ebi) != elimBlocks.end())
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ebi = ebi.Erase();
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else
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++ebi;
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return modified;
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}
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void DeadBranchElimPass::Initialize(ir::Module* module) {
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module_ = module;
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// Initialize function and block maps
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id2function_.clear();
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id2block_.clear();
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block2structured_succs_.clear();
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for (auto& fn : *module_) {
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// Initialize function and block maps.
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id2function_[fn.result_id()] = &fn;
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for (auto& blk : fn) {
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id2block_[blk.id()] = &blk;
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}
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}
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// TODO(greg-lunarg): Reuse def/use from previous passes
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def_use_mgr_.reset(new analysis::DefUseManager(consumer(), module_));
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// Initialize extension whitelist
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InitExtensions();
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};
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bool DeadBranchElimPass::AllExtensionsSupported() const {
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// If any extension not in whitelist, return false
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for (auto& ei : module_->extensions()) {
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const char* extName = reinterpret_cast<const char*>(
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&ei.GetInOperand(0).words[0]);
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if (extensions_whitelist_.find(extName) == extensions_whitelist_.end())
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return false;
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}
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return true;
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}
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Pass::Status DeadBranchElimPass::ProcessImpl() {
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// Current functionality assumes structured control flow.
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// TODO(greg-lunarg): Handle non-structured control-flow.
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if (!module_->HasCapability(SpvCapabilityShader))
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return Status::SuccessWithoutChange;
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// Do not process if any disallowed extensions are enabled
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if (!AllExtensionsSupported())
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return Status::SuccessWithoutChange;
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// Process all entry point functions
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bool modified = false;
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for (const auto& e : module_->entry_points()) {
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ir::Function* fn =
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id2function_[e.GetSingleWordInOperand(kEntryPointFunctionIdInIdx)];
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modified = EliminateDeadBranches(fn) || modified;
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}
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return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
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}
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DeadBranchElimPass::DeadBranchElimPass()
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: module_(nullptr), def_use_mgr_(nullptr) {}
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Pass::Status DeadBranchElimPass::Process(ir::Module* module) {
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Initialize(module);
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return ProcessImpl();
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}
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void DeadBranchElimPass::InitExtensions() {
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extensions_whitelist_.clear();
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extensions_whitelist_.insert({
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"SPV_AMD_shader_explicit_vertex_parameter",
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"SPV_AMD_shader_trinary_minmax",
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"SPV_AMD_gcn_shader",
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"SPV_KHR_shader_ballot",
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"SPV_AMD_shader_ballot",
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"SPV_AMD_gpu_shader_half_float",
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"SPV_KHR_shader_draw_parameters",
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"SPV_KHR_subgroup_vote",
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"SPV_KHR_16bit_storage",
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"SPV_KHR_device_group",
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"SPV_KHR_multiview",
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"SPV_NVX_multiview_per_view_attributes",
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"SPV_NV_viewport_array2",
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"SPV_NV_stereo_view_rendering",
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"SPV_NV_sample_mask_override_coverage",
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"SPV_NV_geometry_shader_passthrough",
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"SPV_AMD_texture_gather_bias_lod",
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"SPV_KHR_storage_buffer_storage_class",
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"SPV_KHR_variable_pointers",
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"SPV_AMD_gpu_shader_int16",
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"SPV_KHR_post_depth_coverage",
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"SPV_KHR_shader_atomic_counter_ops",
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});
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}
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} // namespace opt
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} // namespace spvtools
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