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https://github.com/KhronosGroup/SPIRV-Tools
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6c7db9c630
* Handle nested breaks from switches.
There was a recent decision made to allow branches to the merge node of
a switch even if the switch is not the first enclosing construct. They
can be generated by glslang from break statements in switches.
Dead branch elimination seems to be the only optimization that will
break because of this change, so I will update that optimizations.
The change made are:
- Track switches in structured cfg analysis.
- In Dead branch elimination:
- Look for nested breaks that will require a switch instruction.
- Rewrite, but don't delete, switchs that are required even if it
could be replaced by an unconditional branch.
- When looking for the first break, consider the merge of a switch
as well.
See #2612.
* Fix variable names and comments.
* Add tests for the struct cfg analysis and switches.
* Fix typos in comments.
123 lines
4.3 KiB
C++
123 lines
4.3 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_STRUCT_CFG_ANALYSIS_H_
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#define SOURCE_OPT_STRUCT_CFG_ANALYSIS_H_
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#include <unordered_map>
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#include "source/opt/function.h"
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#include "source/util/bit_vector.h"
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namespace spvtools {
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namespace opt {
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class IRContext;
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// An analysis that, for each basic block, finds the constructs in which it is
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// contained, so we can easily get headers and merge nodes.
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class StructuredCFGAnalysis {
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public:
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explicit StructuredCFGAnalysis(IRContext* ctx);
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// Returns the id of the header of the innermost merge construct
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// that contains |bb_id|. Returns |0| if |bb_id| is not contained in any
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// merge construct.
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uint32_t ContainingConstruct(uint32_t bb_id) {
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auto it = bb_to_construct_.find(bb_id);
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if (it == bb_to_construct_.end()) {
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return 0;
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}
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return it->second.containing_construct;
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}
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// Returns the id of the header of the innermost merge construct
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// that contains |inst|. Returns |0| if |inst| is not contained in any
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// merge construct.
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uint32_t ContainingConstruct(Instruction* inst);
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// Returns the id of the merge block of the innermost merge construct
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// that contains |bb_id|. Returns |0| if |bb_id| is not contained in any
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// merge construct.
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uint32_t MergeBlock(uint32_t bb_id);
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// Returns the id of the header of the innermost loop construct
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// that contains |bb_id|. Return |0| if |bb_id| is not contained in any loop
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// construct.
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uint32_t ContainingLoop(uint32_t bb_id) {
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auto it = bb_to_construct_.find(bb_id);
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if (it == bb_to_construct_.end()) {
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return 0;
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}
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return it->second.containing_loop;
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}
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// Returns the id of the merge block of the innermost loop construct
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// that contains |bb_id|. Return |0| if |bb_id| is not contained in any loop
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// construct.
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uint32_t LoopMergeBlock(uint32_t bb_id);
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// Returns the id of the continue block of the innermost loop construct
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// that contains |bb_id|. Return |0| if |bb_id| is not contained in any loop
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// construct.
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uint32_t LoopContinueBlock(uint32_t bb_id);
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// Returns the id of the header of the innermost switch construct
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// that contains |bb_id| as long as there is no intervening loop. Returns |0|
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// if no such construct exists.
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uint32_t ContainingSwitch(uint32_t bb_id) {
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auto it = bb_to_construct_.find(bb_id);
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if (it == bb_to_construct_.end()) {
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return 0;
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}
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return it->second.containing_switch;
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}
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// Returns the id of the merge block of the innermost switch construct
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// that contains |bb_id| as long as there is no intervening loop. Return |0|
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// if no such block exists.
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uint32_t SwitchMergeBlock(uint32_t bb_id);
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bool IsContinueBlock(uint32_t bb_id);
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bool IsMergeBlock(uint32_t bb_id);
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private:
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// Struct used to hold the information for a basic block.
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// |containing_construct| is the header for the innermost containing
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// construct, or 0 if no such construct exists. It could be a selection
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// construct or a loop construct. |containing_loop| is the innermost
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// containing loop construct, or 0 if the basic bloc is not in a loop. If the
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// basic block is in a selection construct that is contained in a loop
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// construct, then these two values will not be the same.
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struct ConstructInfo {
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uint32_t containing_construct;
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uint32_t containing_loop;
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uint32_t containing_switch;
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};
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// Populates |bb_to_construct_| with the innermost containing merge and loop
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// constructs for each basic block in |func|.
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void AddBlocksInFunction(Function* func);
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IRContext* context_;
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// A map from a basic block to the headers of its inner most containing
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// constructs.
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std::unordered_map<uint32_t, ConstructInfo> bb_to_construct_;
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utils::BitVector merge_blocks_;
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};
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} // namespace opt
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} // namespace spvtools
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#endif // SOURCE_OPT_STRUCT_CFG_ANALYSIS_H_
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