SPIRV-Tools/source/opt/unify_const_pass.cpp
Steven Perron 65046eca7c Change IRContext::KillInst to delete instructions.
The current method of removing an instruction is to call ToNop.  The
problem with this is that it leaves around an instruction that later
passes will look at.  We should just delete the instruction.

In MemPass there is a utility routine called DCEInst.  It can delete
essentially any instruction, which can invalidate pointers now that they
are actually deleted.  The interface was changed to add a call back that
can be used to update any local data structures that contain
ir::Intruction*.
2017-12-04 11:07:45 -05:00

175 lines
6.9 KiB
C++

// Copyright (c) 2016 Google 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 "unify_const_pass.h"
#include <unordered_map>
#include <utility>
#include "def_use_manager.h"
#include "ir_context.h"
#include "make_unique.h"
namespace spvtools {
namespace opt {
namespace {
// The trie that stores a bunch of result ids and, for a given instruction,
// searches the result id that has been defined with the same opcode, type and
// operands.
class ResultIdTrie {
public:
ResultIdTrie() : root_(new Node) {}
// For a given instruction, extracts its opcode, type id and operand words
// as an array of keys, looks up the trie to find a result id which is stored
// with the same opcode, type id and operand words. If none of such result id
// is found, creates a trie node with those keys, stores the instruction's
// result id and returns that result id. If an existing result id is found,
// returns the existing result id.
uint32_t LookupEquivalentResultFor(const ir::Instruction& inst) {
auto keys = GetLookUpKeys(inst);
auto* node = root_.get();
for (uint32_t key : keys) {
node = node->GetOrCreateTrieNodeFor(key);
}
if (node->result_id() == 0) {
node->SetResultId(inst.result_id());
}
return node->result_id();
}
private:
// The trie node to store result ids.
class Node {
public:
using TrieNodeMap = std::unordered_map<uint32_t, std::unique_ptr<Node>>;
Node() : result_id_(0), next_() {}
uint32_t result_id() const { return result_id_; }
// Sets the result id stored in this node.
void SetResultId(uint32_t id) { result_id_ = id; }
// Searches for the child trie node with the given key. If the node is
// found, returns that node. Otherwise creates an empty child node with
// that key and returns that newly created node.
Node* GetOrCreateTrieNodeFor(uint32_t key) {
auto iter = next_.find(key);
if (iter == next_.end()) {
// insert a new node and return the node.
return next_.insert(std::make_pair(key, MakeUnique<Node>()))
.first->second.get();
}
return iter->second.get();
}
private:
// The result id stored in this node. 0 means this node is empty.
uint32_t result_id_;
// The mapping from the keys to the child nodes of this node.
TrieNodeMap next_;
};
// Returns a vector of the opcode followed by the words in the raw SPIR-V
// instruction encoding but without the result id.
std::vector<uint32_t> GetLookUpKeys(const ir::Instruction& inst) {
std::vector<uint32_t> keys;
// Need to use the opcode, otherwise there might be a conflict with the
// following case when <op>'s binary value equals xx's id:
// OpSpecConstantOp tt <op> yy zz
// OpSpecConstantComposite tt xx yy zz;
keys.push_back(static_cast<uint32_t>(inst.opcode()));
for (const auto& operand : inst) {
if (operand.type == SPV_OPERAND_TYPE_RESULT_ID) continue;
keys.insert(keys.end(), operand.words.cbegin(), operand.words.cend());
}
return keys;
}
std::unique_ptr<Node> root_; // The root node of the trie.
};
} // anonymous namespace
Pass::Status UnifyConstantPass::Process(ir::IRContext* c) {
InitializeProcessing(c);
bool modified = false;
ResultIdTrie defined_constants;
for( ir::Instruction* next_instruction, *inst = &*(context()->types_values_begin()); inst; inst = next_instruction) {
next_instruction = inst->NextNode();
// Do not handle the instruction when there are decorations upon the result
// id.
if (get_def_use_mgr()->GetAnnotations(inst->result_id()).size() != 0) {
continue;
}
// The overall algorithm is to store the result ids of all the eligible
// constants encountered so far in a trie. For a constant defining
// instruction under consideration, use its opcode, result type id and
// words in operands as an array of keys to lookup the trie. If a result id
// can be found for that array of keys, a constant with exactly the same
// value must has been defined before, the constant under processing
// should be replaced by the constant previously defined. If no such result
// id can be found for that array of keys, this must be the first time a
// constant with its value be defined, we then create a new trie node to
// store the result id with the keys. When replacing a duplicated constant
// with a previously defined constant, all the uses of the duplicated
// constant, which must be placed after the duplicated constant defining
// instruction, will be updated. This way, the descendants of the
// previously defined constant and the duplicated constant will both refer
// to the previously defined constant. So that the operand ids which are
// used in key arrays will be the ids of the unified constants, when
// processing is up to a descendant. This makes comparing the key array
// always valid for judging duplication.
switch (inst->opcode()) {
case SpvOp::SpvOpConstantTrue:
case SpvOp::SpvOpConstantFalse:
case SpvOp::SpvOpConstant:
case SpvOp::SpvOpConstantNull:
case SpvOp::SpvOpConstantSampler:
case SpvOp::SpvOpConstantComposite:
// Only spec constants defined with OpSpecConstantOp and
// OpSpecConstantComposite should be processed in this pass. Spec
// constants defined with OpSpecConstant{|True|False} are decorated with
// 'SpecId' decoration and all of them should be treated as unique.
// 'SpecId' is not applicable to SpecConstants defined with
// OpSpecConstant{Op|Composite}, their values are not necessary to be
// unique. When all the operands/compoents are the same between two
// OpSpecConstant{Op|Composite} results, their result values must be the
// same so are unifiable.
case SpvOp::SpvOpSpecConstantOp:
case SpvOp::SpvOpSpecConstantComposite: {
uint32_t id = defined_constants.LookupEquivalentResultFor(*inst);
if (id != inst->result_id()) {
// The constant is a duplicated one, use the cached constant to
// replace the uses of this duplicated one, then turn it to nop.
context()->ReplaceAllUsesWith(inst->result_id(), id);
context()->KillInst(inst);
modified = true;
}
break;
}
default:
break;
}
}
return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange;
}
} // namespace opt
} // namespace spvtools