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SPIRV-Tools/source/opt/local_ssa_elim_pass.cpp

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// Copyright (c) 2017 The Khronos Group Inc.
// Copyright (c) 2017 Valve Corporation
// Copyright (c) 2017 LunarG Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "local_ssa_elim_pass.h"
#include "iterator.h"
#include "cfa.h"
namespace spvtools {
namespace opt {
namespace {
const uint32_t kStoreValIdInIdx = 1;
const uint32_t kTypePointerTypeIdInIdx = 1;
const uint32_t kSelectionMergeMergeBlockIdInIdx = 0;
const uint32_t kLoopMergeMergeBlockIdInIdx = 0;
const uint32_t kLoopMergeContinueBlockIdInIdx = 1;
} // anonymous namespace
bool LocalMultiStoreElimPass::HasOnlySupportedRefs(uint32_t varId) {
if (supported_ref_vars_.find(varId) != supported_ref_vars_.end())
return true;
analysis::UseList* uses = def_use_mgr_->GetUses(varId);
if (uses == nullptr)
return true;
for (auto u : *uses) {
const SpvOp op = u.inst->opcode();
if (op != SpvOpStore && op != SpvOpLoad && op != SpvOpName &&
!IsNonTypeDecorate(op))
return false;
}
supported_ref_vars_.insert(varId);
return true;
}
void LocalMultiStoreElimPass::InitSSARewrite(ir::Function& func) {
// Init predecessors
label2preds_.clear();
for (auto& blk : func) {
uint32_t blkId = blk.id();
blk.ForEachSuccessorLabel([&blkId, this](uint32_t sbid) {
label2preds_[sbid].push_back(blkId);
});
}
// Collect target (and non-) variable sets. Remove variables with
// non-load/store refs from target variable set
for (auto& blk : func) {
for (auto& inst : blk) {
switch (inst.opcode()) {
case SpvOpStore:
case SpvOpLoad: {
uint32_t varId;
(void) GetPtr(&inst, &varId);
if (!IsTargetVar(varId))
break;
if (HasOnlySupportedRefs(varId))
break;
seen_non_target_vars_.insert(varId);
seen_target_vars_.erase(varId);
} break;
default:
break;
}
}
}
}
uint32_t LocalMultiStoreElimPass::MergeBlockIdIfAny(const ir::BasicBlock& blk,
uint32_t* cbid) {
auto merge_ii = blk.cend();
--merge_ii;
*cbid = 0;
uint32_t mbid = 0;
if (merge_ii != blk.cbegin()) {
--merge_ii;
if (merge_ii->opcode() == SpvOpLoopMerge) {
mbid = merge_ii->GetSingleWordInOperand(kLoopMergeMergeBlockIdInIdx);
*cbid = merge_ii->GetSingleWordInOperand(kLoopMergeContinueBlockIdInIdx);
}
else if (merge_ii->opcode() == SpvOpSelectionMerge) {
mbid = merge_ii->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx);
}
}
return mbid;
}
void LocalMultiStoreElimPass::ComputeStructuredSuccessors(ir::Function* func) {
block2structured_succs_.clear();
for (auto& blk : *func) {
// If no predecessors in function, make successor to pseudo entry
if (label2preds_[blk.id()].size() == 0)
block2structured_succs_[&pseudo_entry_block_].push_back(&blk);
// If header, make merge block first successor.
uint32_t cbid;
const uint32_t mbid = MergeBlockIdIfAny(blk, &cbid);
if (mbid != 0) {
block2structured_succs_[&blk].push_back(id2block_[mbid]);
if (cbid != 0)
block2structured_succs_[&blk].push_back(id2block_[cbid]);
}
// add true successors
blk.ForEachSuccessorLabel([&blk, this](uint32_t sbid) {
block2structured_succs_[&blk].push_back(id2block_[sbid]);
});
}
}
void LocalMultiStoreElimPass::ComputeStructuredOrder(
ir::Function* func, std::list<ir::BasicBlock*>* order) {
// Compute structured successors and do DFS
ComputeStructuredSuccessors(func);
auto ignore_block = [](cbb_ptr) {};
auto ignore_edge = [](cbb_ptr, cbb_ptr) {};
auto get_structured_successors = [this](const ir::BasicBlock* block) {
return &(block2structured_succs_[block]); };
// TODO(greg-lunarg): Get rid of const_cast by making moving const
// out of the cfa.h prototypes and into the invoking code.
auto post_order = [&](cbb_ptr b) {
order->push_front(const_cast<ir::BasicBlock*>(b)); };
spvtools::CFA<ir::BasicBlock>::DepthFirstTraversal(
&pseudo_entry_block_, get_structured_successors, ignore_block,
post_order, ignore_edge);
}
void LocalMultiStoreElimPass::SSABlockInitSinglePred(ir::BasicBlock* block_ptr) {
// Copy map entry from single predecessor
const uint32_t label = block_ptr->id();
const uint32_t predLabel = label2preds_[label].front();
assert(visitedBlocks_.find(predLabel) != visitedBlocks_.end());
label2ssa_map_[label] = label2ssa_map_[predLabel];
}
bool LocalMultiStoreElimPass::IsLiveAfter(uint32_t var_id, uint32_t label) const {
// For now, return very conservative result: true. This will result in
// correct, but possibly usused, phi code to be generated. A subsequent
// DCE pass should eliminate this code.
// TODO(greg-lunarg): Return more accurate information
(void) var_id;
(void) label;
return true;
}
uint32_t LocalMultiStoreElimPass::Type2Undef(uint32_t type_id) {
const auto uitr = type2undefs_.find(type_id);
if (uitr != type2undefs_.end())
return uitr->second;
const uint32_t undefId = TakeNextId();
std::unique_ptr<ir::Instruction> undef_inst(
new ir::Instruction(SpvOpUndef, type_id, undefId, {}));
def_use_mgr_->AnalyzeInstDefUse(&*undef_inst);
module_->AddGlobalValue(std::move(undef_inst));
type2undefs_[type_id] = undefId;
return undefId;
}
uint32_t LocalMultiStoreElimPass::GetPointeeTypeId(
const ir::Instruction* ptrInst) const {
const uint32_t ptrTypeId = ptrInst->type_id();
const ir::Instruction* ptrTypeInst = def_use_mgr_->GetDef(ptrTypeId);
return ptrTypeInst->GetSingleWordInOperand(kTypePointerTypeIdInIdx);
}
void LocalMultiStoreElimPass::SSABlockInitLoopHeader(
std::list<ir::BasicBlock*>::iterator block_itr) {
const uint32_t label = (*block_itr)->id();
// Determine backedge label.
uint32_t backLabel = 0;
for (uint32_t predLabel : label2preds_[label])
if (visitedBlocks_.find(predLabel) == visitedBlocks_.end()) {
assert(backLabel == 0);
backLabel = predLabel;
break;
}
assert(backLabel != 0);
// Determine merge block.
auto mergeInst = (*block_itr)->end();
--mergeInst;
--mergeInst;
uint32_t mergeLabel = mergeInst->GetSingleWordInOperand(
kLoopMergeMergeBlockIdInIdx);
// Collect all live variables and a default value for each across all
// non-backedge predecesors. Must be ordered map because phis are
// generated based on order and test results will otherwise vary across
// platforms.
std::map<uint32_t, uint32_t> liveVars;
for (uint32_t predLabel : label2preds_[label]) {
for (auto var_val : label2ssa_map_[predLabel]) {
uint32_t varId = var_val.first;
liveVars[varId] = var_val.second;
}
}
// Add all stored variables in loop. Set their default value id to zero.
for (auto bi = block_itr; (*bi)->id() != mergeLabel; ++bi) {
ir::BasicBlock* bp = *bi;
for (auto ii = bp->begin(); ii != bp->end(); ++ii) {
if (ii->opcode() != SpvOpStore)
continue;
uint32_t varId;
(void) GetPtr(&*ii, &varId);
if (!IsTargetVar(varId))
continue;
liveVars[varId] = 0;
}
}
// Insert phi for all live variables that require them. All variables
// defined in loop require a phi. Otherwise all variables
// with differing predecessor values require a phi.
auto insertItr = (*block_itr)->begin();
for (auto var_val : liveVars) {
const uint32_t varId = var_val.first;
if (!IsLiveAfter(varId, label))
continue;
const uint32_t val0Id = var_val.second;
bool needsPhi = false;
if (val0Id != 0) {
for (uint32_t predLabel : label2preds_[label]) {
// Skip back edge predecessor.
if (predLabel == backLabel)
continue;
const auto var_val_itr = label2ssa_map_[predLabel].find(varId);
// Missing (undef) values always cause difference with (defined) value
if (var_val_itr == label2ssa_map_[predLabel].end()) {
needsPhi = true;
break;
}
if (var_val_itr->second != val0Id) {
needsPhi = true;
break;
}
}
}
else {
needsPhi = true;
}
// If val is the same for all predecessors, enter it in map
if (!needsPhi) {
label2ssa_map_[label].insert(var_val);
continue;
}
// Val differs across predecessors. Add phi op to block and
// add its result id to the map. For back edge predecessor,
// use the variable id. We will patch this after visiting back
// edge predecessor. For predecessors that do not define a value,
// use undef.
std::vector<ir::Operand> phi_in_operands;
uint32_t typeId = GetPointeeTypeId(def_use_mgr_->GetDef(varId));
for (uint32_t predLabel : label2preds_[label]) {
uint32_t valId;
if (predLabel == backLabel) {
valId = varId;
}
else {
const auto var_val_itr = label2ssa_map_[predLabel].find(varId);
if (var_val_itr == label2ssa_map_[predLabel].end())
valId = Type2Undef(typeId);
else
valId = var_val_itr->second;
}
phi_in_operands.push_back(
{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {valId}});
phi_in_operands.push_back(
{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {predLabel}});
}
const uint32_t phiId = TakeNextId();
std::unique_ptr<ir::Instruction> newPhi(
new ir::Instruction(SpvOpPhi, typeId, phiId, phi_in_operands));
// The only phis requiring patching are the ones we create.
phis_to_patch_.insert(phiId);
// Only analyze the phi define now; analyze the phi uses after the
// phi backedge predecessor value is patched.
def_use_mgr_->AnalyzeInstDef(&*newPhi);
insertItr = insertItr.InsertBefore(std::move(newPhi));
++insertItr;
label2ssa_map_[label].insert({ varId, phiId });
}
}
void LocalMultiStoreElimPass::SSABlockInitMultiPred(ir::BasicBlock* block_ptr) {
const uint32_t label = block_ptr->id();
// Collect all live variables and a default value for each across all
// predecesors. Must be ordered map because phis are generated based on
// order and test results will otherwise vary across platforms.
std::map<uint32_t, uint32_t> liveVars;
for (uint32_t predLabel : label2preds_[label]) {
assert(visitedBlocks_.find(predLabel) != visitedBlocks_.end());
for (auto var_val : label2ssa_map_[predLabel]) {
const uint32_t varId = var_val.first;
liveVars[varId] = var_val.second;
}
}
// For each live variable, look for a difference in values across
// predecessors that would require a phi and insert one.
auto insertItr = block_ptr->begin();
for (auto var_val : liveVars) {
const uint32_t varId = var_val.first;
if (!IsLiveAfter(varId, label))
continue;
const uint32_t val0Id = var_val.second;
bool differs = false;
for (uint32_t predLabel : label2preds_[label]) {
const auto var_val_itr = label2ssa_map_[predLabel].find(varId);
// Missing values cause a difference because we'll need to create an
// undef for that predecessor.
if (var_val_itr == label2ssa_map_[predLabel].end()) {
differs = true;
break;
}
if (var_val_itr->second != val0Id) {
differs = true;
break;
}
}
// If val is the same for all predecessors, enter it in map
if (!differs) {
label2ssa_map_[label].insert(var_val);
continue;
}
// Val differs across predecessors. Add phi op to block and
// add its result id to the map
std::vector<ir::Operand> phi_in_operands;
const uint32_t typeId = GetPointeeTypeId(def_use_mgr_->GetDef(varId));
for (uint32_t predLabel : label2preds_[label]) {
const auto var_val_itr = label2ssa_map_[predLabel].find(varId);
// If variable not defined on this path, use undef
const uint32_t valId = (var_val_itr != label2ssa_map_[predLabel].end()) ?
var_val_itr->second : Type2Undef(typeId);
phi_in_operands.push_back(
{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {valId}});
phi_in_operands.push_back(
{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {predLabel}});
}
const uint32_t phiId = TakeNextId();
std::unique_ptr<ir::Instruction> newPhi(
new ir::Instruction(SpvOpPhi, typeId, phiId, phi_in_operands));
def_use_mgr_->AnalyzeInstDefUse(&*newPhi);
insertItr = insertItr.InsertBefore(std::move(newPhi));
++insertItr;
label2ssa_map_[label].insert({varId, phiId});
}
}
bool LocalMultiStoreElimPass::IsLoopHeader(ir::BasicBlock* block_ptr) const {
auto iItr = block_ptr->end();
--iItr;
if (iItr == block_ptr->begin())
return false;
--iItr;
return iItr->opcode() == SpvOpLoopMerge;
}
void LocalMultiStoreElimPass::SSABlockInit(
std::list<ir::BasicBlock*>::iterator block_itr) {
const size_t numPreds = label2preds_[(*block_itr)->id()].size();
if (numPreds == 0)
return;
if (numPreds == 1)
SSABlockInitSinglePred(*block_itr);
else if (IsLoopHeader(*block_itr))
SSABlockInitLoopHeader(block_itr);
else
SSABlockInitMultiPred(*block_itr);
}
void LocalMultiStoreElimPass::PatchPhis(uint32_t header_id, uint32_t back_id) {
ir::BasicBlock* header = id2block_[header_id];
auto phiItr = header->begin();
for (; phiItr->opcode() == SpvOpPhi; ++phiItr) {
// Only patch phis that we created in a loop header.
// There might be other phis unrelated to our optimizations.
if (0 == phis_to_patch_.count(phiItr->result_id())) continue;
// Find phi operand index for back edge
uint32_t cnt = 0;
uint32_t idx = phiItr->NumInOperands();
phiItr->ForEachInId([&cnt,&back_id,&idx](uint32_t* iid) {
if (cnt % 2 == 1 && *iid == back_id) idx = cnt - 1;
++cnt;
});
assert(idx != phiItr->NumInOperands());
// Replace temporary phi operand with variable's value in backedge block
// map. Use undef if variable not in map.
const uint32_t varId = phiItr->GetSingleWordInOperand(idx);
const auto valItr = label2ssa_map_[back_id].find(varId);
uint32_t valId =
(valItr != label2ssa_map_[back_id].end())
? valItr->second
: Type2Undef(GetPointeeTypeId(def_use_mgr_->GetDef(varId)));
phiItr->SetInOperand(idx, {valId});
// Analyze uses now that they are complete
def_use_mgr_->AnalyzeInstUse(&*phiItr);
}
}
bool LocalMultiStoreElimPass::EliminateMultiStoreLocal(ir::Function* func) {
InitSSARewrite(*func);
// Process all blocks in structured order. This is just one way (the
// simplest?) to make sure all predecessors blocks are processed before
// a block itself.
std::list<ir::BasicBlock*> structuredOrder;
ComputeStructuredOrder(func, &structuredOrder);
bool modified = false;
for (auto bi = structuredOrder.begin(); bi != structuredOrder.end(); ++bi) {
// Skip pseudo entry block
if (*bi == &pseudo_entry_block_)
continue;
// Initialize this block's label2ssa_map_ entry using predecessor maps.
// Then process all stores and loads of targeted variables.
SSABlockInit(bi);
ir::BasicBlock* bp = *bi;
const uint32_t label = bp->id();
for (auto ii = bp->begin(); ii != bp->end(); ++ii) {
switch (ii->opcode()) {
case SpvOpStore: {
uint32_t varId;
(void) GetPtr(&*ii, &varId);
if (!IsTargetVar(varId))
break;
// Register new stored value for the variable
label2ssa_map_[label][varId] =
ii->GetSingleWordInOperand(kStoreValIdInIdx);
} break;
case SpvOpLoad: {
uint32_t varId;
(void) GetPtr(&*ii, &varId);
if (!IsTargetVar(varId))
break;
uint32_t replId = 0;
const auto ssaItr = label2ssa_map_.find(label);
if (ssaItr != label2ssa_map_.end()) {
const auto valItr = ssaItr->second.find(varId);
if (valItr != ssaItr->second.end())
replId = valItr->second;
}
// If variable is not defined, use undef
if (replId == 0) {
replId = Type2Undef(GetPointeeTypeId(def_use_mgr_->GetDef(varId)));
}
// Replace load's id with the last stored value id for variable
// and delete load. Kill any names or decorates using id before
// replacing to prevent incorrect replacement in those instructions.
const uint32_t loadId = ii->result_id();
KillNamesAndDecorates(loadId);
(void)def_use_mgr_->ReplaceAllUsesWith(loadId, replId);
def_use_mgr_->KillInst(&*ii);
modified = true;
} break;
default: {
} break;
}
}
visitedBlocks_.insert(label);
// Look for successor backedge and patch phis in loop header
// if found.
uint32_t header = 0;
bp->ForEachSuccessorLabel([&header,this](uint32_t succ) {
if (visitedBlocks_.find(succ) == visitedBlocks_.end()) return;
assert(header == 0);
header = succ;
});
if (header != 0)
PatchPhis(header, label);
}
// Remove all target variable stores.
for (auto bi = func->begin(); bi != func->end(); ++bi) {
for (auto ii = bi->begin(); ii != bi->end(); ++ii) {
if (ii->opcode() != SpvOpStore)
continue;
uint32_t varId;
(void) GetPtr(&*ii, &varId);
if (!IsTargetVar(varId))
continue;
assert(!HasLoads(varId));
DCEInst(&*ii);
modified = true;
}
}
return modified;
}
void LocalMultiStoreElimPass::Initialize(ir::Module* module) {
module_ = module;
// TODO(greg-lunarg): Reuse def/use from previous passes
def_use_mgr_.reset(new analysis::DefUseManager(consumer(), module_));
// Initialize function and block maps
id2block_.clear();
block2structured_succs_.clear();
for (auto& fn : *module_)
for (auto& blk : fn)
id2block_[blk.id()] = &blk;
// Clear collections
seen_target_vars_.clear();
seen_non_target_vars_.clear();
visitedBlocks_.clear();
type2undefs_.clear();
supported_ref_vars_.clear();
block2structured_succs_.clear();
label2preds_.clear();
label2ssa_map_.clear();
phis_to_patch_.clear();
// Start new ids with next availablein module
InitNextId();
// Initialize extension whitelist
InitExtensions();
};
bool LocalMultiStoreElimPass::AllExtensionsSupported() const {
// If any extension not in whitelist, return false
for (auto& ei : module_->extensions()) {
const char* extName = reinterpret_cast<const char*>(
&ei.GetInOperand(0).words[0]);
if (extensions_whitelist_.find(extName) == extensions_whitelist_.end())
return false;
}
return true;
}
Pass::Status LocalMultiStoreElimPass::ProcessImpl() {
// Assumes all control flow structured.
// TODO(greg-lunarg): Do SSA rewrite for non-structured control flow
if (!module_->HasCapability(SpvCapabilityShader))
return Status::SuccessWithoutChange;
// Assumes logical addressing only
// TODO(greg-lunarg): Add support for physical addressing
if (module_->HasCapability(SpvCapabilityAddresses))
return Status::SuccessWithoutChange;
// Do not process if module contains OpGroupDecorate. Additional
// support required in KillNamesAndDecorates().
// TODO(greg-lunarg): Add support for OpGroupDecorate
for (auto& ai : module_->annotations())
if (ai.opcode() == SpvOpGroupDecorate)
return Status::SuccessWithoutChange;
// Do not process if any disallowed extensions are enabled
if (!AllExtensionsSupported())
return Status::SuccessWithoutChange;
// Collect all named and decorated ids
FindNamedOrDecoratedIds();
// Process functions
ProcessFunction pfn = [this](ir::Function* fp) {
return EliminateMultiStoreLocal(fp);
};
bool modified = ProcessEntryPointCallTree(pfn, module_);
FinalizeNextId();
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}
LocalMultiStoreElimPass::LocalMultiStoreElimPass()
: pseudo_entry_block_(std::unique_ptr<ir::Instruction>(
new ir::Instruction(SpvOpLabel, 0, 0, {}))) {}
Pass::Status LocalMultiStoreElimPass::Process(ir::Module* module) {
Initialize(module);
return ProcessImpl();
}
void LocalMultiStoreElimPass::InitExtensions() {
extensions_whitelist_.clear();
extensions_whitelist_.insert({
"SPV_AMD_shader_explicit_vertex_parameter",
"SPV_AMD_shader_trinary_minmax",
"SPV_AMD_gcn_shader",
"SPV_KHR_shader_ballot",
"SPV_AMD_shader_ballot",
"SPV_AMD_gpu_shader_half_float",
"SPV_KHR_shader_draw_parameters",
"SPV_KHR_subgroup_vote",
"SPV_KHR_16bit_storage",
"SPV_KHR_device_group",
"SPV_KHR_multiview",
"SPV_NVX_multiview_per_view_attributes",
"SPV_NV_viewport_array2",
"SPV_NV_stereo_view_rendering",
"SPV_NV_sample_mask_override_coverage",
"SPV_NV_geometry_shader_passthrough",
"SPV_AMD_texture_gather_bias_lod",
"SPV_KHR_storage_buffer_storage_class",
// SPV_KHR_variable_pointers
// Currently do not support extended pointer expressions
"SPV_AMD_gpu_shader_int16",
"SPV_KHR_post_depth_coverage",
"SPV_KHR_shader_atomic_counter_ops",
});
}
} // namespace opt
} // namespace spvtools
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