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SPIRV-Tools/source/opt/aggressive_dead_code_elim_pass.cpp
Ehsan e6f372c5c2
Whitelist SPV_KHR_ray_tracing (#3241)
2020-03-23 09:31:05 -05:00

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// Copyright (c) 2017 The Khronos Group Inc.
// Copyright (c) 2017 Valve Corporation
// Copyright (c) 2017 LunarG Inc.
// Copyright (c) 2018 Google LLC
//
// 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 "source/opt/aggressive_dead_code_elim_pass.h"
#include <memory>
#include <stack>
#include "source/cfa.h"
#include "source/latest_version_glsl_std_450_header.h"
#include "source/opt/iterator.h"
#include "source/opt/reflect.h"
#include "source/spirv_constant.h"
namespace spvtools {
namespace opt {
namespace {
const uint32_t kTypePointerStorageClassInIdx = 0;
const uint32_t kEntryPointFunctionIdInIdx = 1;
const uint32_t kSelectionMergeMergeBlockIdInIdx = 0;
const uint32_t kLoopMergeMergeBlockIdInIdx = 0;
const uint32_t kLoopMergeContinueBlockIdInIdx = 1;
const uint32_t kCopyMemoryTargetAddrInIdx = 0;
const uint32_t kCopyMemorySourceAddrInIdx = 1;
// Sorting functor to present annotation instructions in an easy-to-process
// order. The functor orders by opcode first and falls back on unique id
// ordering if both instructions have the same opcode.
//
// Desired priority:
// SpvOpGroupDecorate
// SpvOpGroupMemberDecorate
// SpvOpDecorate
// SpvOpMemberDecorate
// SpvOpDecorateId
// SpvOpDecorateStringGOOGLE
// SpvOpDecorationGroup
struct DecorationLess {
bool operator()(const Instruction* lhs, const Instruction* rhs) const {
assert(lhs && rhs);
SpvOp lhsOp = lhs->opcode();
SpvOp rhsOp = rhs->opcode();
if (lhsOp != rhsOp) {
#define PRIORITY_CASE(opcode) \
if (lhsOp == opcode && rhsOp != opcode) return true; \
if (rhsOp == opcode && lhsOp != opcode) return false;
// OpGroupDecorate and OpGroupMember decorate are highest priority to
// eliminate dead targets early and simplify subsequent checks.
PRIORITY_CASE(SpvOpGroupDecorate)
PRIORITY_CASE(SpvOpGroupMemberDecorate)
PRIORITY_CASE(SpvOpDecorate)
PRIORITY_CASE(SpvOpMemberDecorate)
PRIORITY_CASE(SpvOpDecorateId)
PRIORITY_CASE(SpvOpDecorateStringGOOGLE)
// OpDecorationGroup is lowest priority to ensure use/def chains remain
// usable for instructions that target this group.
PRIORITY_CASE(SpvOpDecorationGroup)
#undef PRIORITY_CASE
}
// Fall back to maintain total ordering (compare unique ids).
return *lhs < *rhs;
}
};
} // namespace
bool AggressiveDCEPass::IsVarOfStorage(uint32_t varId, uint32_t storageClass) {
if (varId == 0) return false;
const Instruction* varInst = get_def_use_mgr()->GetDef(varId);
const SpvOp op = varInst->opcode();
if (op != SpvOpVariable) return false;
const uint32_t varTypeId = varInst->type_id();
const Instruction* varTypeInst = get_def_use_mgr()->GetDef(varTypeId);
if (varTypeInst->opcode() != SpvOpTypePointer) return false;
return varTypeInst->GetSingleWordInOperand(kTypePointerStorageClassInIdx) ==
storageClass;
}
bool AggressiveDCEPass::IsLocalVar(uint32_t varId) {
if (IsVarOfStorage(varId, SpvStorageClassFunction)) {
return true;
}
if (!private_like_local_) {
return false;
}
return IsVarOfStorage(varId, SpvStorageClassPrivate) ||
IsVarOfStorage(varId, SpvStorageClassWorkgroup);
}
void AggressiveDCEPass::AddStores(uint32_t ptrId) {
get_def_use_mgr()->ForEachUser(ptrId, [this, ptrId](Instruction* user) {
switch (user->opcode()) {
case SpvOpAccessChain:
case SpvOpInBoundsAccessChain:
case SpvOpCopyObject:
this->AddStores(user->result_id());
break;
case SpvOpLoad:
break;
case SpvOpCopyMemory:
case SpvOpCopyMemorySized:
if (user->GetSingleWordInOperand(kCopyMemoryTargetAddrInIdx) == ptrId) {
AddToWorklist(user);
}
break;
// If default, assume it stores e.g. frexp, modf, function call
case SpvOpStore:
default:
AddToWorklist(user);
break;
}
});
}
bool AggressiveDCEPass::AllExtensionsSupported() const {
// If any extension not in whitelist, return false
for (auto& ei : get_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;
}
bool AggressiveDCEPass::IsDead(Instruction* inst) {
if (IsLive(inst)) return false;
if ((inst->IsBranch() || inst->opcode() == SpvOpUnreachable) &&
!IsStructuredHeader(context()->get_instr_block(inst), nullptr, nullptr,
nullptr))
return false;
return true;
}
bool AggressiveDCEPass::IsTargetDead(Instruction* inst) {
const uint32_t tId = inst->GetSingleWordInOperand(0);
Instruction* tInst = get_def_use_mgr()->GetDef(tId);
if (IsAnnotationInst(tInst->opcode())) {
// This must be a decoration group. We go through annotations in a specific
// order. So if this is not used by any group or group member decorates, it
// is dead.
assert(tInst->opcode() == SpvOpDecorationGroup);
bool dead = true;
get_def_use_mgr()->ForEachUser(tInst, [&dead](Instruction* user) {
if (user->opcode() == SpvOpGroupDecorate ||
user->opcode() == SpvOpGroupMemberDecorate)
dead = false;
});
return dead;
}
return IsDead(tInst);
}
void AggressiveDCEPass::ProcessLoad(uint32_t varId) {
// Only process locals
if (!IsLocalVar(varId)) return;
// Return if already processed
if (live_local_vars_.find(varId) != live_local_vars_.end()) return;
// Mark all stores to varId as live
AddStores(varId);
// Cache varId as processed
live_local_vars_.insert(varId);
}
bool AggressiveDCEPass::IsStructuredHeader(BasicBlock* bp,
Instruction** mergeInst,
Instruction** branchInst,
uint32_t* mergeBlockId) {
if (!bp) return false;
Instruction* mi = bp->GetMergeInst();
if (mi == nullptr) return false;
Instruction* bri = &*bp->tail();
if (branchInst != nullptr) *branchInst = bri;
if (mergeInst != nullptr) *mergeInst = mi;
if (mergeBlockId != nullptr) *mergeBlockId = mi->GetSingleWordInOperand(0);
return true;
}
void AggressiveDCEPass::ComputeBlock2HeaderMaps(
std::list<BasicBlock*>& structuredOrder) {
block2headerBranch_.clear();
header2nextHeaderBranch_.clear();
branch2merge_.clear();
structured_order_index_.clear();
std::stack<Instruction*> currentHeaderBranch;
currentHeaderBranch.push(nullptr);
uint32_t currentMergeBlockId = 0;
uint32_t index = 0;
for (auto bi = structuredOrder.begin(); bi != structuredOrder.end();
++bi, ++index) {
structured_order_index_[*bi] = index;
// If this block is the merge block of the current control construct,
// we are leaving the current construct so we must update state
if ((*bi)->id() == currentMergeBlockId) {
currentHeaderBranch.pop();
Instruction* chb = currentHeaderBranch.top();
if (chb != nullptr)
currentMergeBlockId = branch2merge_[chb]->GetSingleWordInOperand(0);
}
Instruction* mergeInst;
Instruction* branchInst;
uint32_t mergeBlockId;
bool is_header =
IsStructuredHeader(*bi, &mergeInst, &branchInst, &mergeBlockId);
// Map header block to next enclosing header.
if (is_header) header2nextHeaderBranch_[*bi] = currentHeaderBranch.top();
// If this is a loop header, update state first so the block will map to
// itself.
if (is_header && mergeInst->opcode() == SpvOpLoopMerge) {
currentHeaderBranch.push(branchInst);
branch2merge_[branchInst] = mergeInst;
currentMergeBlockId = mergeBlockId;
}
// Map the block to the current construct.
block2headerBranch_[*bi] = currentHeaderBranch.top();
// If this is an if header, update state so following blocks map to the if.
if (is_header && mergeInst->opcode() == SpvOpSelectionMerge) {
currentHeaderBranch.push(branchInst);
branch2merge_[branchInst] = mergeInst;
currentMergeBlockId = mergeBlockId;
}
}
}
void AggressiveDCEPass::AddBranch(uint32_t labelId, BasicBlock* bp) {
std::unique_ptr<Instruction> newBranch(
new Instruction(context(), SpvOpBranch, 0, 0,
{{spv_operand_type_t::SPV_OPERAND_TYPE_ID, {labelId}}}));
context()->AnalyzeDefUse(&*newBranch);
context()->set_instr_block(&*newBranch, bp);
bp->AddInstruction(std::move(newBranch));
}
void AggressiveDCEPass::AddBreaksAndContinuesToWorklist(
Instruction* mergeInst) {
assert(mergeInst->opcode() == SpvOpSelectionMerge ||
mergeInst->opcode() == SpvOpLoopMerge);
BasicBlock* header = context()->get_instr_block(mergeInst);
uint32_t headerIndex = structured_order_index_[header];
const uint32_t mergeId = mergeInst->GetSingleWordInOperand(0);
BasicBlock* merge = context()->get_instr_block(mergeId);
uint32_t mergeIndex = structured_order_index_[merge];
get_def_use_mgr()->ForEachUser(
mergeId, [headerIndex, mergeIndex, this](Instruction* user) {
if (!user->IsBranch()) return;
BasicBlock* block = context()->get_instr_block(user);
uint32_t index = structured_order_index_[block];
if (headerIndex < index && index < mergeIndex) {
// This is a break from the loop.
AddToWorklist(user);
// Add branch's merge if there is one.
Instruction* userMerge = branch2merge_[user];
if (userMerge != nullptr) AddToWorklist(userMerge);
}
});
if (mergeInst->opcode() != SpvOpLoopMerge) {
return;
}
// For loops we need to find the continues as well.
const uint32_t contId =
mergeInst->GetSingleWordInOperand(kLoopMergeContinueBlockIdInIdx);
get_def_use_mgr()->ForEachUser(contId, [&contId, this](Instruction* user) {
SpvOp op = user->opcode();
if (op == SpvOpBranchConditional || op == SpvOpSwitch) {
// A conditional branch or switch can only be a continue if it does not
// have a merge instruction or its merge block is not the continue block.
Instruction* hdrMerge = branch2merge_[user];
if (hdrMerge != nullptr && hdrMerge->opcode() == SpvOpSelectionMerge) {
uint32_t hdrMergeId =
hdrMerge->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx);
if (hdrMergeId == contId) return;
// Need to mark merge instruction too
AddToWorklist(hdrMerge);
}
} else if (op == SpvOpBranch) {
// An unconditional branch can only be a continue if it is not
// branching to its own merge block.
BasicBlock* blk = context()->get_instr_block(user);
Instruction* hdrBranch = block2headerBranch_[blk];
if (hdrBranch == nullptr) return;
Instruction* hdrMerge = branch2merge_[hdrBranch];
if (hdrMerge->opcode() == SpvOpLoopMerge) return;
uint32_t hdrMergeId =
hdrMerge->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx);
if (contId == hdrMergeId) return;
} else {
return;
}
AddToWorklist(user);
});
}
bool AggressiveDCEPass::AggressiveDCE(Function* func) {
// Mark function parameters as live.
AddToWorklist(&func->DefInst());
func->ForEachParam(
[this](const Instruction* param) {
AddToWorklist(const_cast<Instruction*>(param));
},
false);
// Compute map from block to controlling conditional branch
std::list<BasicBlock*> structuredOrder;
cfg()->ComputeStructuredOrder(func, &*func->begin(), &structuredOrder);
ComputeBlock2HeaderMaps(structuredOrder);
bool modified = false;
// Add instructions with external side effects to worklist. Also add branches
// EXCEPT those immediately contained in an "if" selection construct or a loop
// or continue construct.
// TODO(greg-lunarg): Handle Frexp, Modf more optimally
call_in_func_ = false;
func_is_entry_point_ = false;
private_stores_.clear();
// Stacks to keep track of when we are inside an if- or loop-construct.
// When immediately inside an if- or loop-construct, we do not initially
// mark branches live. All other branches must be marked live.
std::stack<bool> assume_branches_live;
std::stack<uint32_t> currentMergeBlockId;
// Push sentinel values on stack for when outside of any control flow.
assume_branches_live.push(true);
currentMergeBlockId.push(0);
for (auto bi = structuredOrder.begin(); bi != structuredOrder.end(); ++bi) {
// If exiting if or loop, update stacks
if ((*bi)->id() == currentMergeBlockId.top()) {
assume_branches_live.pop();
currentMergeBlockId.pop();
}
for (auto ii = (*bi)->begin(); ii != (*bi)->end(); ++ii) {
SpvOp op = ii->opcode();
switch (op) {
case SpvOpStore: {
uint32_t varId;
(void)GetPtr(&*ii, &varId);
// Mark stores as live if their variable is not function scope
// and is not private scope. Remember private stores for possible
// later inclusion. We cannot call IsLocalVar at this point because
// private_like_local_ has not been set yet.
if (IsVarOfStorage(varId, SpvStorageClassPrivate) ||
IsVarOfStorage(varId, SpvStorageClassWorkgroup))
private_stores_.push_back(&*ii);
else if (!IsVarOfStorage(varId, SpvStorageClassFunction))
AddToWorklist(&*ii);
} break;
case SpvOpCopyMemory:
case SpvOpCopyMemorySized: {
uint32_t varId;
(void)GetPtr(ii->GetSingleWordInOperand(kCopyMemoryTargetAddrInIdx),
&varId);
if (IsVarOfStorage(varId, SpvStorageClassPrivate) ||
IsVarOfStorage(varId, SpvStorageClassWorkgroup))
private_stores_.push_back(&*ii);
else if (!IsVarOfStorage(varId, SpvStorageClassFunction))
AddToWorklist(&*ii);
} break;
case SpvOpLoopMerge: {
assume_branches_live.push(false);
currentMergeBlockId.push(
ii->GetSingleWordInOperand(kLoopMergeMergeBlockIdInIdx));
} break;
case SpvOpSelectionMerge: {
assume_branches_live.push(false);
currentMergeBlockId.push(
ii->GetSingleWordInOperand(kSelectionMergeMergeBlockIdInIdx));
} break;
case SpvOpSwitch:
case SpvOpBranch:
case SpvOpBranchConditional:
case SpvOpUnreachable: {
if (assume_branches_live.top()) {
AddToWorklist(&*ii);
}
} break;
default: {
// Function calls, atomics, function params, function returns, etc.
// TODO(greg-lunarg): function calls live only if write to non-local
if (!ii->IsOpcodeSafeToDelete()) {
AddToWorklist(&*ii);
}
// Remember function calls
if (op == SpvOpFunctionCall) call_in_func_ = true;
} break;
}
}
}
// See if current function is an entry point
for (auto& ei : get_module()->entry_points()) {
if (ei.GetSingleWordInOperand(kEntryPointFunctionIdInIdx) ==
func->result_id()) {
func_is_entry_point_ = true;
break;
}
}
// If the current function is an entry point and has no function calls,
// we can optimize private variables as locals
private_like_local_ = func_is_entry_point_ && !call_in_func_;
// If privates are not like local, add their stores to worklist
if (!private_like_local_)
for (auto& ps : private_stores_) AddToWorklist(ps);
// Perform closure on live instruction set.
while (!worklist_.empty()) {
Instruction* liveInst = worklist_.front();
// Add all operand instructions if not already live
liveInst->ForEachInId([&liveInst, this](const uint32_t* iid) {
Instruction* inInst = get_def_use_mgr()->GetDef(*iid);
// Do not add label if an operand of a branch. This is not needed
// as part of live code discovery and can create false live code,
// for example, the branch to a header of a loop.
if (inInst->opcode() == SpvOpLabel && liveInst->IsBranch()) return;
AddToWorklist(inInst);
});
if (liveInst->type_id() != 0) {
AddToWorklist(get_def_use_mgr()->GetDef(liveInst->type_id()));
}
// If in a structured if or loop construct, add the controlling
// conditional branch and its merge.
BasicBlock* blk = context()->get_instr_block(liveInst);
Instruction* branchInst = block2headerBranch_[blk];
if (branchInst != nullptr) {
AddToWorklist(branchInst);
Instruction* mergeInst = branch2merge_[branchInst];
AddToWorklist(mergeInst);
}
// If the block is a header, add the next outermost controlling
// conditional branch and its merge.
Instruction* nextBranchInst = header2nextHeaderBranch_[blk];
if (nextBranchInst != nullptr) {
AddToWorklist(nextBranchInst);
Instruction* mergeInst = branch2merge_[nextBranchInst];
AddToWorklist(mergeInst);
}
// If local load, add all variable's stores if variable not already live
if (liveInst->opcode() == SpvOpLoad || liveInst->IsAtomicWithLoad()) {
uint32_t varId;
(void)GetPtr(liveInst, &varId);
if (varId != 0) {
ProcessLoad(varId);
}
// Process memory copies like loads
} else if (liveInst->opcode() == SpvOpCopyMemory ||
liveInst->opcode() == SpvOpCopyMemorySized) {
uint32_t varId;
(void)GetPtr(liveInst->GetSingleWordInOperand(kCopyMemorySourceAddrInIdx),
&varId);
if (varId != 0) {
ProcessLoad(varId);
}
// If merge, add other branches that are part of its control structure
} else if (liveInst->opcode() == SpvOpLoopMerge ||
liveInst->opcode() == SpvOpSelectionMerge) {
AddBreaksAndContinuesToWorklist(liveInst);
// If function call, treat as if it loads from all pointer arguments
} else if (liveInst->opcode() == SpvOpFunctionCall) {
liveInst->ForEachInId([this](const uint32_t* iid) {
// Skip non-ptr args
if (!IsPtr(*iid)) return;
uint32_t varId;
(void)GetPtr(*iid, &varId);
ProcessLoad(varId);
});
// If function parameter, treat as if it's result id is loaded from
} else if (liveInst->opcode() == SpvOpFunctionParameter) {
ProcessLoad(liveInst->result_id());
// We treat an OpImageTexelPointer as a load of the pointer, and
// that value is manipulated to get the result.
} else if (liveInst->opcode() == SpvOpImageTexelPointer) {
uint32_t varId;
(void)GetPtr(liveInst, &varId);
if (varId != 0) {
ProcessLoad(varId);
}
}
// Add OpDecorateId instructions that apply to this instruction to the work
// list. We use the decoration manager to look through the group
// decorations to get to the OpDecorate* instructions themselves.
auto decorations =
get_decoration_mgr()->GetDecorationsFor(liveInst->result_id(), false);
for (Instruction* dec : decorations) {
// We only care about OpDecorateId instructions because the are the only
// decorations that will reference an id that will have to be kept live
// because of that use.
if (dec->opcode() != SpvOpDecorateId) {
continue;
}
if (dec->GetSingleWordInOperand(1) ==
SpvDecorationHlslCounterBufferGOOGLE) {
// These decorations should not force the use id to be live. It will be
// removed if either the target or the in operand are dead.
continue;
}
AddToWorklist(dec);
}
worklist_.pop();
}
// Kill dead instructions and remember dead blocks
for (auto bi = structuredOrder.begin(); bi != structuredOrder.end();) {
uint32_t mergeBlockId = 0;
(*bi)->ForEachInst([this, &modified, &mergeBlockId](Instruction* inst) {
if (!IsDead(inst)) return;
if (inst->opcode() == SpvOpLabel) return;
// If dead instruction is selection merge, remember merge block
// for new branch at end of block
if (inst->opcode() == SpvOpSelectionMerge ||
inst->opcode() == SpvOpLoopMerge)
mergeBlockId = inst->GetSingleWordInOperand(0);
to_kill_.push_back(inst);
modified = true;
});
// If a structured if or loop was deleted, add a branch to its merge
// block, and traverse to the merge block and continue processing there.
// We know the block still exists because the label is not deleted.
if (mergeBlockId != 0) {
AddBranch(mergeBlockId, *bi);
for (++bi; (*bi)->id() != mergeBlockId; ++bi) {
}
auto merge_terminator = (*bi)->terminator();
if (merge_terminator->opcode() == SpvOpUnreachable) {
// The merge was unreachable. This is undefined behaviour so just
// return (or return an undef). Then mark the new return as live.
auto func_ret_type_inst = get_def_use_mgr()->GetDef(func->type_id());
if (func_ret_type_inst->opcode() == SpvOpTypeVoid) {
merge_terminator->SetOpcode(SpvOpReturn);
} else {
// Find an undef for the return value and make sure it gets kept by
// the pass.
auto undef_id = Type2Undef(func->type_id());
auto undef = get_def_use_mgr()->GetDef(undef_id);
live_insts_.Set(undef->unique_id());
merge_terminator->SetOpcode(SpvOpReturnValue);
merge_terminator->SetInOperands({{SPV_OPERAND_TYPE_ID, {undef_id}}});
get_def_use_mgr()->AnalyzeInstUse(merge_terminator);
}
live_insts_.Set(merge_terminator->unique_id());
}
} else {
++bi;
}
}
return modified;
}
void AggressiveDCEPass::InitializeModuleScopeLiveInstructions() {
// Keep all execution modes.
for (auto& exec : get_module()->execution_modes()) {
AddToWorklist(&exec);
}
// Keep all entry points.
for (auto& entry : get_module()->entry_points()) {
if (get_module()->version() >= SPV_SPIRV_VERSION_WORD(1, 4)) {
// In SPIR-V 1.4 and later, entry points must list all global variables
// used. DCE can still remove non-input/output variables and update the
// interface list. Mark the entry point as live and inputs and outputs as
// live, but defer decisions all other interfaces.
live_insts_.Set(entry.unique_id());
// The actual function is live always.
AddToWorklist(
get_def_use_mgr()->GetDef(entry.GetSingleWordInOperand(1u)));
for (uint32_t i = 3; i < entry.NumInOperands(); ++i) {
auto* var = get_def_use_mgr()->GetDef(entry.GetSingleWordInOperand(i));
auto storage_class = var->GetSingleWordInOperand(0u);
if (storage_class == SpvStorageClassInput ||
storage_class == SpvStorageClassOutput) {
AddToWorklist(var);
}
}
} else {
AddToWorklist(&entry);
}
}
for (auto& anno : get_module()->annotations()) {
if (anno.opcode() == SpvOpDecorate) {
// Keep workgroup size.
if (anno.GetSingleWordInOperand(1u) == SpvDecorationBuiltIn &&
anno.GetSingleWordInOperand(2u) == SpvBuiltInWorkgroupSize) {
AddToWorklist(&anno);
}
if (context()->preserve_bindings()) {
// Keep all bindings.
if ((anno.GetSingleWordInOperand(1u) == SpvDecorationDescriptorSet) ||
(anno.GetSingleWordInOperand(1u) == SpvDecorationBinding)) {
AddToWorklist(&anno);
}
}
if (context()->preserve_spec_constants()) {
// Keep all specialization constant instructions
if (anno.GetSingleWordInOperand(1u) == SpvDecorationSpecId) {
AddToWorklist(&anno);
}
}
}
}
}
Pass::Status AggressiveDCEPass::ProcessImpl() {
// Current functionality assumes shader capability
// TODO(greg-lunarg): Handle additional capabilities
if (!context()->get_feature_mgr()->HasCapability(SpvCapabilityShader))
return Status::SuccessWithoutChange;
// Current functionality assumes relaxed logical addressing (see
// instruction.h)
// TODO(greg-lunarg): Handle non-logical addressing
if (context()->get_feature_mgr()->HasCapability(SpvCapabilityAddresses))
return Status::SuccessWithoutChange;
// The variable pointer extension is no longer needed to use the capability,
// so we have to look for the capability.
if (context()->get_feature_mgr()->HasCapability(
SpvCapabilityVariablePointersStorageBuffer))
return Status::SuccessWithoutChange;
// If any extensions in the module are not explicitly supported,
// return unmodified.
if (!AllExtensionsSupported()) return Status::SuccessWithoutChange;
// Eliminate Dead functions.
bool modified = EliminateDeadFunctions();
InitializeModuleScopeLiveInstructions();
// Process all entry point functions.
ProcessFunction pfn = [this](Function* fp) { return AggressiveDCE(fp); };
modified |= context()->ProcessEntryPointCallTree(pfn);
// If the decoration manager is kept live then the context will try to keep it
// up to date. ADCE deals with group decorations by changing the operands in
// |OpGroupDecorate| instruction directly without informing the decoration
// manager. This can put it in an invalid state which will cause an error
// when the context tries to update it. To avoid this problem invalidate
// the decoration manager upfront.
//
// We kill it at now because it is used when processing the entry point
// functions.
context()->InvalidateAnalyses(IRContext::Analysis::kAnalysisDecorations);
// Process module-level instructions. Now that all live instructions have
// been marked, it is safe to remove dead global values.
modified |= ProcessGlobalValues();
// Sanity check.
assert(to_kill_.size() == 0 || modified);
// Kill all dead instructions.
for (auto inst : to_kill_) {
context()->KillInst(inst);
}
// Cleanup all CFG including all unreachable blocks.
ProcessFunction cleanup = [this](Function* f) { return CFGCleanup(f); };
modified |= context()->ProcessEntryPointCallTree(cleanup);
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}
bool AggressiveDCEPass::EliminateDeadFunctions() {
// Identify live functions first. Those that are not live
// are dead. ADCE is disabled for non-shaders so we do not check for exported
// functions here.
std::unordered_set<const Function*> live_function_set;
ProcessFunction mark_live = [&live_function_set](Function* fp) {
live_function_set.insert(fp);
return false;
};
context()->ProcessEntryPointCallTree(mark_live);
bool modified = false;
for (auto funcIter = get_module()->begin();
funcIter != get_module()->end();) {
if (live_function_set.count(&*funcIter) == 0) {
modified = true;
EliminateFunction(&*funcIter);
funcIter = funcIter.Erase();
} else {
++funcIter;
}
}
return modified;
}
void AggressiveDCEPass::EliminateFunction(Function* func) {
// Remove all of the instruction in the function body
func->ForEachInst([this](Instruction* inst) { context()->KillInst(inst); },
true);
}
bool AggressiveDCEPass::ProcessGlobalValues() {
// Remove debug and annotation statements referencing dead instructions.
// This must be done before killing the instructions, otherwise there are
// dead objects in the def/use database.
bool modified = false;
Instruction* instruction = &*get_module()->debug2_begin();
while (instruction) {
if (instruction->opcode() != SpvOpName) {
instruction = instruction->NextNode();
continue;
}
if (IsTargetDead(instruction)) {
instruction = context()->KillInst(instruction);
modified = true;
} else {
instruction = instruction->NextNode();
}
}
// This code removes all unnecessary decorations safely (see #1174). It also
// does so in a more efficient manner than deleting them only as the targets
// are deleted.
std::vector<Instruction*> annotations;
for (auto& inst : get_module()->annotations()) annotations.push_back(&inst);
std::sort(annotations.begin(), annotations.end(), DecorationLess());
for (auto annotation : annotations) {
switch (annotation->opcode()) {
case SpvOpDecorate:
case SpvOpMemberDecorate:
case SpvOpDecorateStringGOOGLE:
case SpvOpMemberDecorateStringGOOGLE:
if (IsTargetDead(annotation)) {
context()->KillInst(annotation);
modified = true;
}
break;
case SpvOpDecorateId:
if (IsTargetDead(annotation)) {
context()->KillInst(annotation);
modified = true;
} else {
if (annotation->GetSingleWordInOperand(1) ==
SpvDecorationHlslCounterBufferGOOGLE) {
// HlslCounterBuffer will reference an id other than the target.
// If that id is dead, then the decoration can be removed as well.
uint32_t counter_buffer_id = annotation->GetSingleWordInOperand(2);
Instruction* counter_buffer_inst =
get_def_use_mgr()->GetDef(counter_buffer_id);
if (IsDead(counter_buffer_inst)) {
context()->KillInst(annotation);
modified = true;
}
}
}
break;
case SpvOpGroupDecorate: {
// Go through the targets of this group decorate. Remove each dead
// target. If all targets are dead, remove this decoration.
bool dead = true;
bool removed_operand = false;
for (uint32_t i = 1; i < annotation->NumOperands();) {
Instruction* opInst =
get_def_use_mgr()->GetDef(annotation->GetSingleWordOperand(i));
if (IsDead(opInst)) {
// Don't increment |i|.
annotation->RemoveOperand(i);
modified = true;
removed_operand = true;
} else {
i++;
dead = false;
}
}
if (dead) {
context()->KillInst(annotation);
modified = true;
} else if (removed_operand) {
context()->UpdateDefUse(annotation);
}
break;
}
case SpvOpGroupMemberDecorate: {
// Go through the targets of this group member decorate. Remove each
// dead target (and member index). If all targets are dead, remove this
// decoration.
bool dead = true;
bool removed_operand = false;
for (uint32_t i = 1; i < annotation->NumOperands();) {
Instruction* opInst =
get_def_use_mgr()->GetDef(annotation->GetSingleWordOperand(i));
if (IsDead(opInst)) {
// Don't increment |i|.
annotation->RemoveOperand(i + 1);
annotation->RemoveOperand(i);
modified = true;
removed_operand = true;
} else {
i += 2;
dead = false;
}
}
if (dead) {
context()->KillInst(annotation);
modified = true;
} else if (removed_operand) {
context()->UpdateDefUse(annotation);
}
break;
}
case SpvOpDecorationGroup:
// By the time we hit decoration groups we've checked everything that
// can target them. So if they have no uses they must be dead.
if (get_def_use_mgr()->NumUsers(annotation) == 0) {
context()->KillInst(annotation);
modified = true;
}
break;
default:
assert(false);
break;
}
}
// Since ADCE is disabled for non-shaders, we don't check for export linkage
// attributes here.
for (auto& val : get_module()->types_values()) {
if (IsDead(&val)) {
// Save forwarded pointer if pointer is live since closure does not mark
// this live as it does not have a result id. This is a little too
// conservative since it is not known if the structure type that needed
// it is still live. TODO(greg-lunarg): Only save if needed.
if (val.opcode() == SpvOpTypeForwardPointer) {
uint32_t ptr_ty_id = val.GetSingleWordInOperand(0);
Instruction* ptr_ty_inst = get_def_use_mgr()->GetDef(ptr_ty_id);
if (!IsDead(ptr_ty_inst)) continue;
}
to_kill_.push_back(&val);
modified = true;
}
}
if (get_module()->version() >= SPV_SPIRV_VERSION_WORD(1, 4)) {
// Remove the dead interface variables from the entry point interface list.
for (auto& entry : get_module()->entry_points()) {
std::vector<Operand> new_operands;
for (uint32_t i = 0; i < entry.NumInOperands(); ++i) {
if (i < 3) {
// Execution model, function id and name are always valid.
new_operands.push_back(entry.GetInOperand(i));
} else {
auto* var =
get_def_use_mgr()->GetDef(entry.GetSingleWordInOperand(i));
if (!IsDead(var)) {
new_operands.push_back(entry.GetInOperand(i));
}
}
}
if (new_operands.size() != entry.NumInOperands()) {
entry.SetInOperands(std::move(new_operands));
get_def_use_mgr()->UpdateDefUse(&entry);
}
}
}
return modified;
}
AggressiveDCEPass::AggressiveDCEPass() = default;
Pass::Status AggressiveDCEPass::Process() {
// Initialize extensions whitelist
InitExtensions();
return ProcessImpl();
}
void AggressiveDCEPass::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",
"SPV_EXT_shader_stencil_export",
"SPV_EXT_shader_viewport_index_layer",
"SPV_AMD_shader_image_load_store_lod",
"SPV_AMD_shader_fragment_mask",
"SPV_EXT_fragment_fully_covered",
"SPV_AMD_gpu_shader_half_float_fetch",
"SPV_GOOGLE_decorate_string",
"SPV_GOOGLE_hlsl_functionality1",
"SPV_GOOGLE_user_type",
"SPV_NV_shader_subgroup_partitioned",
"SPV_EXT_demote_to_helper_invocation",
"SPV_EXT_descriptor_indexing",
"SPV_NV_fragment_shader_barycentric",
"SPV_NV_compute_shader_derivatives",
"SPV_NV_shader_image_footprint",
"SPV_NV_shading_rate",
"SPV_NV_mesh_shader",
"SPV_NV_ray_tracing",
"SPV_KHR_ray_tracing",
"SPV_EXT_fragment_invocation_density",
"SPV_EXT_physical_storage_buffer",
});
}
} // namespace opt
} // namespace spvtools
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