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https://github.com/KhronosGroup/SPIRV-Tools
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1dc2458060
This pass will look for adjacent loops that are compatible and legal to
be fused.
Loops are compatible if:
- they both have one induction variable
- they have the same upper and lower bounds
- same initial value
- same condition
- they have the same update step
- they are adjacent
- there are no break/continue in either of them
Fusion is legal if:
- fused loops do not have any dependencies with dependence distance
greater than 0 that did not exist in the original loops.
- there are no function calls in the loops (could have side-effects)
- there are no barriers in the loops
It will fuse all such loops as long as the number of registers used for
the fused loop stays under the threshold defined by
max_registers_per_loop.
115 lines
3.9 KiB
C++
115 lines
3.9 KiB
C++
// Copyright (c) 2018 Google LLC.
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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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#ifndef SOURCE_OPT_LOOP_FUSION_H_
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#define SOURCE_OPT_LOOP_FUSION_H_
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#include <map>
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#include <set>
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#include <vector>
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#include "opt/ir_context.h"
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#include "opt/loop_descriptor.h"
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#include "opt/loop_utils.h"
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#include "opt/scalar_analysis.h"
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namespace spvtools {
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namespace opt {
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class LoopFusion {
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public:
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LoopFusion(ir::IRContext* context, ir::Loop* loop_0, ir::Loop* loop_1)
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: context_(context),
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loop_0_(loop_0),
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loop_1_(loop_1),
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containing_function_(loop_0->GetHeaderBlock()->GetParent()) {}
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// Checks if the |loop_0| and |loop_1| are compatible for fusion.
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// That means:
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// * they both have one induction variable
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// * they have the same upper and lower bounds
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// - same inital value
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// - same condition
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// * they have the same update step
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// * they are adjacent, with |loop_0| appearing before |loop_1|
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// * there are no break/continue in either of them
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// * they both have pre-header blocks (required for ScalarEvolutionAnalysis
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// and dependence checking).
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bool AreCompatible();
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// Checks if compatible |loop_0| and |loop_1| are legal to fuse.
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// * fused loops do not have any dependencies with dependence distance greater
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// than 0 that did not exist in the original loops.
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// * there are no function calls in the loops (could have side-effects)
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bool IsLegal();
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// Perform the actual fusion of |loop_0_| and |loop_1_|. The loops have to be
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// compatible and the fusion has to be legal.
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void Fuse();
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private:
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// Check that the initial values are the same.
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bool CheckInit();
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// Check that the conditions are the same.
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bool CheckCondition();
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// Check that the steps are the same.
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bool CheckStep();
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// Returns |true| if |instruction| is used in the continue or condition block
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// of |loop|.
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bool UsedInContinueOrConditionBlock(ir::Instruction* instruction,
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ir::Loop* loop);
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// Remove entries in |instructions| that are not used in the continue or
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// condition block of |loop|.
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void RemoveIfNotUsedContinueOrConditionBlock(
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std::vector<ir::Instruction*>* instructions, ir::Loop* loop);
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// Returns |true| if |instruction| is used in |loop|.
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bool IsUsedInLoop(ir::Instruction* instruction, ir::Loop* loop);
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// Returns |true| if |loop| has at least one barrier or function call.
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bool ContainsBarriersOrFunctionCalls(ir::Loop* loop);
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// Get all instructions in the |loop| (except in the latch block) that have
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// the opcode |opcode|.
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std::pair<std::vector<ir::Instruction*>, std::vector<ir::Instruction*>>
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GetLoadsAndStoresInLoop(ir::Loop* loop);
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// Given a vector of memory operations (OpLoad/OpStore), constructs a map from
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// variables to the loads/stores that those variables.
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std::map<ir::Instruction*, std::vector<ir::Instruction*>> LocationToMemOps(
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const std::vector<ir::Instruction*>& mem_ops);
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ir::IRContext* context_;
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// The original loops to be fused.
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ir::Loop* loop_0_;
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ir::Loop* loop_1_;
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// The function that contains |loop_0_| and |loop_1_|.
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ir::Function* containing_function_ = nullptr;
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// The induction variables for |loop_0_| and |loop_1_|.
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ir::Instruction* induction_0_ = nullptr;
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ir::Instruction* induction_1_ = nullptr;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_LOOP_FUSION_H_
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