114 lines
4.6 KiB
C++
114 lines
4.6 KiB
C++
//
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// Copyright (C) 2016 Google, Inc.
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions
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// are met:
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//
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// Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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//
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// Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following
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// disclaimer in the documentation and/or other materials provided
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// with the distribution.
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//
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// Neither the name of 3Dlabs Inc. Ltd. nor the names of its
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// contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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// COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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// ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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// POSSIBILITY OF SUCH DAMAGE.
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// The SPIR-V spec requires code blocks to appear in an order satisfying the
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// dominator-tree direction (ie, dominator before the dominated). This is,
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// actually, easy to achieve: any pre-order CFG traversal algorithm will do it.
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// Because such algorithms visit a block only after traversing some path to it
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// from the root, they necessarily visit the block's idom first.
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//
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// But not every graph-traversal algorithm outputs blocks in an order that
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// appears logical to human readers. The problem is that unrelated branches may
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// be interspersed with each other, and merge blocks may come before some of the
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// branches being merged.
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//
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// A good, human-readable order of blocks may be achieved by performing
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// depth-first search but delaying merge nodes until after all their branches
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// have been visited. This is implemented below by the inReadableOrder()
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// function.
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#include "spvIR.h"
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#include <cassert>
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#include <unordered_set>
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using spv::Block;
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using spv::Id;
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namespace {
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// Traverses CFG in a readable order, invoking a pre-set callback on each block.
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// Use by calling visit() on the root block.
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class ReadableOrderTraverser {
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public:
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explicit ReadableOrderTraverser(std::function<void(Block*)> callback) : callback_(callback) {}
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// Visits the block if it hasn't been visited already and isn't currently
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// being delayed. Invokes callback(block), then descends into its
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// successors. Delays merge-block and continue-block processing until all
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// the branches have been completed.
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void visit(Block* block)
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{
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assert(block);
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if (visited_.count(block) || delayed_.count(block))
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return;
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callback_(block);
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visited_.insert(block);
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Block* mergeBlock = nullptr;
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Block* continueBlock = nullptr;
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auto mergeInst = block->getMergeInstruction();
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if (mergeInst) {
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Id mergeId = mergeInst->getIdOperand(0);
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mergeBlock = block->getParent().getParent().getInstruction(mergeId)->getBlock();
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delayed_.insert(mergeBlock);
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if (mergeInst->getOpCode() == spv::OpLoopMerge) {
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Id continueId = mergeInst->getIdOperand(1);
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continueBlock =
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block->getParent().getParent().getInstruction(continueId)->getBlock();
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delayed_.insert(continueBlock);
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}
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}
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const auto successors = block->getSuccessors();
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for (auto it = successors.cbegin(); it != successors.cend(); ++it)
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visit(*it);
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if (continueBlock) {
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delayed_.erase(continueBlock);
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visit(continueBlock);
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}
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if (mergeBlock) {
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delayed_.erase(mergeBlock);
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visit(mergeBlock);
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}
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}
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private:
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std::function<void(Block*)> callback_;
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// Whether a block has already been visited or is being delayed.
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std::unordered_set<Block *> visited_, delayed_;
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};
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}
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void spv::inReadableOrder(Block* root, std::function<void(Block*)> callback)
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{
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ReadableOrderTraverser(callback).visit(root);
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}
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