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SPIRV-Tools/source/opt/code_sink.cpp
alan-baker d35a78db57
Switch SPIRV-Tools to use spirv.hpp11 internally (#4981) 
Fixes #4960

* Switches to using enum classes with an underlying type to avoid
  undefined behaviour
2022-11-04 17:27:10 -04:00

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