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https://github.com/KhronosGroup/SPIRV-Tools
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dd8400e150
This patch adds initial support for loop unrolling in the form of a series of utility classes which perform the unrolling. The pass can be run with the command spirv-opt --loop-unroll. This will unroll loops within the module which have the unroll hint set. The unroller imposes a number of requirements on the loops it can unroll. These are documented in the comments for the LoopUtils::CanPerformUnroll method in loop_utils.h. Some of the restrictions will be lifted in future patches.
114 lines
3.6 KiB
C++
114 lines
3.6 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_UTILS_H_
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#define SOURCE_OPT_LOOP_UTILS_H_
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#include <list>
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#include <memory>
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#include <vector>
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#include "opt/loop_descriptor.h"
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namespace spvtools {
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namespace ir {
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class Loop;
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class IRContext;
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} // namespace ir
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namespace opt {
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// LoopUtils is used to encapsulte loop optimizations and from the passes which
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// use them. Any pass which needs a loop optimization should do it through this
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// or through a pass which is using this.
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class LoopUtils {
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public:
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LoopUtils(ir::IRContext* context, ir::Loop* loop)
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: context_(context),
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loop_(loop),
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function_(*loop_->GetHeaderBlock()->GetParent()) {}
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// The converts the current loop to loop closed SSA form.
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// In the loop closed SSA, all loop exiting values go through a dedicated Phi
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// instruction. For instance:
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//
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// for (...) {
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// A1 = ...
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// if (...)
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// A2 = ...
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// A = phi A1, A2
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// }
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// ... = op A ...
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//
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// Becomes
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//
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// for (...) {
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// A1 = ...
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// if (...)
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// A2 = ...
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// A = phi A1, A2
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// }
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// C = phi A
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// ... = op C ...
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//
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// This makes some loop transformations (such as loop unswitch) simpler
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// (removes the needs to take care of exiting variables).
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void MakeLoopClosedSSA();
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// Create dedicate exit basic block. This ensure all exit basic blocks has the
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// loop as sole predecessors.
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// By construction, structured control flow already has a dedicated exit
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// block.
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// Preserves: CFG, def/use and instruction to block mapping.
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void CreateLoopDedicatedExits();
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// Perfom a partial unroll of |loop| by given |factor|. This will copy the
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// body of the loop |factor| times. So a |factor| of one would give a new loop
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// with the original body plus one unrolled copy body.
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bool PartiallyUnroll(size_t factor);
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// Fully unroll |loop|.
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bool FullyUnroll();
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// This function validates that |loop| meets the assumptions made by the
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// implementation of the loop unroller. As the implementation accommodates
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// more types of loops this function can reduce its checks.
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//
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// The conditions checked to ensure the loop can be unrolled are as follows:
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// 1. That the loop is in structured order.
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// 2. That the condinue block is a branch to the header.
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// 3. That the only phi used in the loop is the induction variable.
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// TODO(stephen@codeplay.com): This is a temporary mesure, after the loop is
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// converted into LCSAA form and has a single entry and exit we can rewrite
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// the other phis.
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// 4. That this is an inner most loop, or that loops contained within this
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// loop have already been fully unrolled.
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// 5. That each instruction in the loop is only used within the loop.
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// (Related to the above phi condition).
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bool CanPerformUnroll();
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// Maintains the loop descriptor object after the unroll functions have been
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// called, otherwise the analysis should be invalidated.
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void Finalize();
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private:
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ir::IRContext* context_;
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ir::Loop* loop_;
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ir::Function& function_;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_LOOP_UTILS_H_
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