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[BOLT] Unifying implementations of ext-tsp
After BOLT's merge to LLVM, there are two (almost identical) versions of the code layout algorithm. The diff unifies the implementations by keeping the one in LLVM. There are mild changes in the resulting block orders. I tested the changes extensively both on the clang binary and on prod services. Didn't see stat sig differences on average. Reviewed By: Amir Differential Revision: https://reviews.llvm.org/D129895
This commit is contained in:
spupyrev
parent
b135358877
commit
539b6c68cb
@ -21,18 +21,9 @@ namespace bolt {
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class BinaryFunction;
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namespace CacheMetrics {
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/// Calculate various metrics related to instruction cache performance.
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/// Calculate and print various metrics related to instruction cache performance
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void printAll(const std::vector<BinaryFunction *> &BinaryFunctions);
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/// Calculate Extended-TSP metric, which quantifies the expected number of
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/// i-cache misses for a given pair of basic blocks. The parameters are:
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/// - SrcAddr is the address of the source block;
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/// - SrcSize is the size of the source block;
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/// - DstAddr is the address of the destination block;
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/// - Count is the number of jumps between the pair of blocks.
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double extTSPScore(uint64_t SrcAddr, uint64_t SrcSize, uint64_t DstAddr,
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uint64_t Count);
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} // namespace CacheMetrics
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} // namespace bolt
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} // namespace llvm
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@ -11,7 +11,6 @@ add_llvm_library(LLVMBOLTPasses
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CallGraphWalker.cpp
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DataflowAnalysis.cpp
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DataflowInfoManager.cpp
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ExtTSPReorderAlgorithm.cpp
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FrameAnalysis.cpp
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FrameOptimizer.cpp
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HFSort.cpp
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@ -53,6 +52,7 @@ add_llvm_library(LLVMBOLTPasses
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AsmPrinter
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MC
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Support
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TransformUtils
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)
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target_link_libraries(LLVMBOLTPasses
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@ -24,10 +24,6 @@ namespace opts {
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extern cl::OptionCategory BoltOptCategory;
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extern cl::opt<double> ForwardWeight;
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extern cl::opt<double> BackwardWeight;
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extern cl::opt<unsigned> ForwardDistance;
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extern cl::opt<unsigned> BackwardDistance;
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extern cl::opt<unsigned> ITLBPageSize;
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extern cl::opt<unsigned> ITLBEntries;
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@ -58,53 +54,30 @@ void extractBasicBlockInfo(
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}
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/// Calculate TSP metric, which quantifies the number of fallthrough jumps in
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/// the ordering of basic blocks
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double
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/// the ordering of basic blocks. The method returns a pair
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/// (the number of fallthrough branches, the total number of branches)
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std::pair<uint64_t, uint64_t>
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calcTSPScore(const std::vector<BinaryFunction *> &BinaryFunctions,
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const std::unordered_map<BinaryBasicBlock *, uint64_t> &BBAddr,
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const std::unordered_map<BinaryBasicBlock *, uint64_t> &BBSize) {
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double Score = 0;
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uint64_t Score = 0;
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uint64_t JumpCount = 0;
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for (BinaryFunction *BF : BinaryFunctions) {
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if (!BF->hasProfile())
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continue;
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for (BinaryBasicBlock &SrcBB : *BF) {
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auto BI = SrcBB.branch_info_begin();
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for (BinaryBasicBlock *DstBB : SrcBB.successors()) {
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if (&SrcBB != DstBB &&
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BI->Count != BinaryBasicBlock::COUNT_NO_PROFILE &&
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BBAddr.at(&SrcBB) + BBSize.at(&SrcBB) == BBAddr.at(DstBB))
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Score += BI->Count;
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for (BinaryBasicBlock *SrcBB : BF->getLayout().blocks()) {
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auto BI = SrcBB->branch_info_begin();
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for (BinaryBasicBlock *DstBB : SrcBB->successors()) {
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if (SrcBB != DstBB && BI->Count != BinaryBasicBlock::COUNT_NO_PROFILE) {
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JumpCount += BI->Count;
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if (BBAddr.at(SrcBB) + BBSize.at(SrcBB) == BBAddr.at(DstBB))
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Score += BI->Count;
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}
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++BI;
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}
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}
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}
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return Score;
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}
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/// Calculate Ext-TSP metric, which quantifies the expected number of i-cache
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/// misses for a given ordering of basic blocks
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double calcExtTSPScore(
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const std::vector<BinaryFunction *> &BinaryFunctions,
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const std::unordered_map<BinaryBasicBlock *, uint64_t> &BBAddr,
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const std::unordered_map<BinaryBasicBlock *, uint64_t> &BBSize) {
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double Score = 0.0;
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for (BinaryFunction *BF : BinaryFunctions) {
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if (!BF->hasProfile())
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continue;
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for (BinaryBasicBlock &SrcBB : *BF) {
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auto BI = SrcBB.branch_info_begin();
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for (BinaryBasicBlock *DstBB : SrcBB.successors()) {
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if (DstBB != &SrcBB)
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Score +=
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CacheMetrics::extTSPScore(BBAddr.at(&SrcBB), BBSize.at(&SrcBB),
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BBAddr.at(DstBB), BI->Count);
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++BI;
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}
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}
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}
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return Score;
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return std::make_pair(Score, JumpCount);
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}
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using Predecessors = std::vector<std::pair<BinaryFunction *, uint64_t>>;
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@ -219,33 +192,6 @@ double expectedCacheHitRatio(
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} // namespace
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double CacheMetrics::extTSPScore(uint64_t SrcAddr, uint64_t SrcSize,
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uint64_t DstAddr, uint64_t Count) {
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assert(Count != BinaryBasicBlock::COUNT_NO_PROFILE);
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// Fallthrough
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if (SrcAddr + SrcSize == DstAddr) {
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// Assume that FallthroughWeight = 1.0 after normalization
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return static_cast<double>(Count);
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}
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// Forward
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if (SrcAddr + SrcSize < DstAddr) {
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const uint64_t Dist = DstAddr - (SrcAddr + SrcSize);
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if (Dist <= opts::ForwardDistance) {
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double Prob = 1.0 - static_cast<double>(Dist) / opts::ForwardDistance;
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return opts::ForwardWeight * Prob * Count;
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}
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return 0;
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}
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// Backward
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const uint64_t Dist = SrcAddr + SrcSize - DstAddr;
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if (Dist <= opts::BackwardDistance) {
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double Prob = 1.0 - static_cast<double>(Dist) / opts::BackwardDistance;
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return opts::BackwardWeight * Prob * Count;
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}
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return 0;
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}
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void CacheMetrics::printAll(const std::vector<BinaryFunction *> &BFs) {
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// Stats related to hot-cold code splitting
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size_t NumFunctions = 0;
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@ -306,9 +252,9 @@ void CacheMetrics::printAll(const std::vector<BinaryFunction *> &BFs) {
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outs() << " Expected i-TLB cache hit ratio: "
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<< format("%.2lf%%\n", expectedCacheHitRatio(BFs, BBAddr, BBSize));
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auto Stats = calcTSPScore(BFs, BBAddr, BBSize);
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outs() << " TSP score: "
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<< format("%.0lf\n", calcTSPScore(BFs, BBAddr, BBSize));
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outs() << " ExtTSP score: "
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<< format("%.0lf\n", calcExtTSPScore(BFs, BBAddr, BBSize));
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<< format("%.2lf%% (%zu out of %zu)\n",
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100.0 * Stats.first / std::max<uint64_t>(Stats.second, 1),
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Stats.first, Stats.second);
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}
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@ -1,889 +0,0 @@
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//===- bolt/Passes/ExtTSPReorderAlgorithm.cpp - Order basic blocks --------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// ExtTSP - layout of basic blocks with i-cache optimization.
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//
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// The algorithm is a greedy heuristic that works with chains (ordered lists)
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// of basic blocks. Initially all chains are isolated basic blocks. On every
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// iteration, we pick a pair of chains whose merging yields the biggest increase
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// in the ExtTSP value, which models how i-cache "friendly" a specific chain is.
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// A pair of chains giving the maximum gain is merged into a new chain. The
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// procedure stops when there is only one chain left, or when merging does not
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// increase ExtTSP. In the latter case, the remaining chains are sorted by
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// density in decreasing order.
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//
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// An important aspect is the way two chains are merged. Unlike earlier
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// algorithms (e.g., OptimizeCacheReorderAlgorithm or Pettis-Hansen), two
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// chains, X and Y, are first split into three, X1, X2, and Y. Then we
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// consider all possible ways of gluing the three chains (e.g., X1YX2, X1X2Y,
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// X2X1Y, X2YX1, YX1X2, YX2X1) and choose the one producing the largest score.
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// This improves the quality of the final result (the search space is larger)
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// while keeping the implementation sufficiently fast.
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//
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// Reference:
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// * A. Newell and S. Pupyrev, Improved Basic Block Reordering,
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// IEEE Transactions on Computers, 2020
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// https://arxiv.org/abs/1809.04676
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//
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//===----------------------------------------------------------------------===//
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#include "bolt/Core/BinaryBasicBlock.h"
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#include "bolt/Core/BinaryFunction.h"
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#include "bolt/Passes/ReorderAlgorithm.h"
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#include "llvm/Support/CommandLine.h"
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using namespace llvm;
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using namespace bolt;
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namespace opts {
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extern cl::OptionCategory BoltOptCategory;
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extern cl::opt<bool> NoThreads;
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cl::opt<unsigned> ChainSplitThreshold(
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"chain-split-threshold",
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cl::desc("The maximum size of a chain to apply splitting"), cl::init(128),
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cl::ReallyHidden, cl::cat(BoltOptCategory));
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cl::opt<double>
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ForwardWeight("forward-weight",
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cl::desc("The weight of forward jumps for ExtTSP value"),
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cl::init(0.1), cl::ReallyHidden, cl::cat(BoltOptCategory));
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cl::opt<double>
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BackwardWeight("backward-weight",
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cl::desc("The weight of backward jumps for ExtTSP value"),
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cl::init(0.1), cl::ReallyHidden, cl::cat(BoltOptCategory));
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cl::opt<unsigned> ForwardDistance(
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"forward-distance",
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cl::desc(
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"The maximum distance (in bytes) of forward jumps for ExtTSP value"),
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cl::init(1024), cl::ReallyHidden, cl::cat(BoltOptCategory));
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cl::opt<unsigned> BackwardDistance(
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"backward-distance",
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cl::desc(
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"The maximum distance (in bytes) of backward jumps for ExtTSP value"),
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cl::init(640), cl::ReallyHidden, cl::cat(BoltOptCategory));
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}
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namespace llvm {
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namespace bolt {
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// Epsilon for comparison of doubles
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constexpr double EPS = 1e-8;
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class Block;
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class Chain;
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class Edge;
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// Calculate Ext-TSP value, which quantifies the expected number of i-cache
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// misses for a given ordering of basic blocks
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double extTSPScore(uint64_t SrcAddr, uint64_t SrcSize, uint64_t DstAddr,
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uint64_t Count) {
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assert(Count != BinaryBasicBlock::COUNT_NO_PROFILE);
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// Fallthrough
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if (SrcAddr + SrcSize == DstAddr) {
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// Assume that FallthroughWeight = 1.0 after normalization
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return static_cast<double>(Count);
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}
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// Forward
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if (SrcAddr + SrcSize < DstAddr) {
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const uint64_t Dist = DstAddr - (SrcAddr + SrcSize);
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if (Dist <= opts::ForwardDistance) {
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double Prob = 1.0 - static_cast<double>(Dist) / opts::ForwardDistance;
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return opts::ForwardWeight * Prob * Count;
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}
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return 0;
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}
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// Backward
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const uint64_t Dist = SrcAddr + SrcSize - DstAddr;
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if (Dist <= opts::BackwardDistance) {
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double Prob = 1.0 - static_cast<double>(Dist) / opts::BackwardDistance;
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return opts::BackwardWeight * Prob * Count;
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}
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return 0;
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}
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using BlockPair = std::pair<Block *, Block *>;
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using JumpList = std::vector<std::pair<BlockPair, uint64_t>>;
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using BlockIter = std::vector<Block *>::const_iterator;
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enum MergeTypeTy {
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X_Y = 0,
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X1_Y_X2 = 1,
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Y_X2_X1 = 2,
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X2_X1_Y = 3,
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};
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class MergeGainTy {
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public:
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explicit MergeGainTy() {}
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explicit MergeGainTy(double Score, size_t MergeOffset, MergeTypeTy MergeType)
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: Score(Score), MergeOffset(MergeOffset), MergeType(MergeType) {}
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double score() const { return Score; }
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size_t mergeOffset() const { return MergeOffset; }
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MergeTypeTy mergeType() const { return MergeType; }
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// returns 'true' iff Other is preferred over this
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bool operator<(const MergeGainTy &Other) const {
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return (Other.Score > EPS && Other.Score > Score + EPS);
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}
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private:
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double Score{-1.0};
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size_t MergeOffset{0};
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MergeTypeTy MergeType{MergeTypeTy::X_Y};
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};
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// A node in CFG corresponding to a BinaryBasicBlock.
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// The class wraps several mutable fields utilized in the ExtTSP algorithm
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class Block {
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public:
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Block(const Block &) = delete;
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Block(Block &&) = default;
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Block &operator=(const Block &) = delete;
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Block &operator=(Block &&) = default;
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// Corresponding basic block
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BinaryBasicBlock *BB{nullptr};
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// Current chain of the basic block
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Chain *CurChain{nullptr};
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// (Estimated) size of the block in the binary
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uint64_t Size{0};
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// Execution count of the block in the binary
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uint64_t ExecutionCount{0};
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// An original index of the node in CFG
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size_t Index{0};
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// The index of the block in the current chain
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size_t CurIndex{0};
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// An offset of the block in the current chain
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mutable uint64_t EstimatedAddr{0};
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// Fallthrough successor of the node in CFG
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Block *FallthroughSucc{nullptr};
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// Fallthrough predecessor of the node in CFG
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Block *FallthroughPred{nullptr};
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// Outgoing jumps from the block
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std::vector<std::pair<Block *, uint64_t>> OutJumps;
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// Incoming jumps to the block
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std::vector<std::pair<Block *, uint64_t>> InJumps;
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// Total execution count of incoming jumps
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uint64_t InWeight{0};
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// Total execution count of outgoing jumps
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uint64_t OutWeight{0};
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public:
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explicit Block(BinaryBasicBlock *BB_, uint64_t Size_)
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: BB(BB_), Size(Size_), ExecutionCount(BB_->getKnownExecutionCount()),
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Index(BB->getLayoutIndex()) {}
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bool adjacent(const Block *Other) const {
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return hasOutJump(Other) || hasInJump(Other);
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}
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bool hasOutJump(const Block *Other) const {
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for (std::pair<Block *, uint64_t> Jump : OutJumps) {
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if (Jump.first == Other)
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return true;
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}
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return false;
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}
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bool hasInJump(const Block *Other) const {
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for (std::pair<Block *, uint64_t> Jump : InJumps) {
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if (Jump.first == Other)
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return true;
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}
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return false;
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}
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};
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// A chain (ordered sequence) of CFG nodes (basic blocks)
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class Chain {
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public:
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Chain(const Chain &) = delete;
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Chain(Chain &&) = default;
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Chain &operator=(const Chain &) = delete;
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Chain &operator=(Chain &&) = default;
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explicit Chain(size_t Id, Block *Block)
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: Id(Id), IsEntry(Block->Index == 0),
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ExecutionCount(Block->ExecutionCount), Size(Block->Size), Score(0),
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Blocks(1, Block) {}
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size_t id() const { return Id; }
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uint64_t size() const { return Size; }
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double density() const { return static_cast<double>(ExecutionCount) / Size; }
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uint64_t executionCount() const { return ExecutionCount; }
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bool isEntryPoint() const { return IsEntry; }
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double score() const { return Score; }
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void setScore(double NewScore) { Score = NewScore; }
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const std::vector<Block *> &blocks() const { return Blocks; }
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const std::vector<std::pair<Chain *, Edge *>> &edges() const { return Edges; }
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Edge *getEdge(Chain *Other) const {
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for (std::pair<Chain *, Edge *> It : Edges)
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if (It.first == Other)
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return It.second;
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return nullptr;
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}
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void removeEdge(Chain *Other) {
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auto It = Edges.begin();
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while (It != Edges.end()) {
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if (It->first == Other) {
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Edges.erase(It);
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return;
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}
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It++;
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}
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}
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void addEdge(Chain *Other, Edge *Edge) { Edges.emplace_back(Other, Edge); }
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void merge(Chain *Other, const std::vector<Block *> &MergedBlocks) {
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Blocks = MergedBlocks;
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IsEntry |= Other->IsEntry;
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ExecutionCount += Other->ExecutionCount;
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Size += Other->Size;
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// Update block's chains
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for (size_t Idx = 0; Idx < Blocks.size(); Idx++) {
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Blocks[Idx]->CurChain = this;
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Blocks[Idx]->CurIndex = Idx;
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}
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}
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void mergeEdges(Chain *Other);
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void clear() {
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Blocks.clear();
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Edges.clear();
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}
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private:
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size_t Id;
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bool IsEntry;
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uint64_t ExecutionCount;
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uint64_t Size;
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// Cached ext-tsp score for the chain
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double Score;
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// Blocks of the chain
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std::vector<Block *> Blocks;
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// Adjacent chains and corresponding edges (lists of jumps)
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std::vector<std::pair<Chain *, Edge *>> Edges;
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};
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||||
|
||||
// An edge in CFG reprsenting jumps between chains of BinaryBasicBlocks.
|
||||
// When blocks are merged into chains, the edges are combined too so that
|
||||
// there is always at most one edge between a pair of chains
|
||||
class Edge {
|
||||
public:
|
||||
Edge(const Edge &) = delete;
|
||||
Edge(Edge &&) = default;
|
||||
Edge &operator=(const Edge &) = delete;
|
||||
Edge &operator=(Edge &&) = default;
|
||||
|
||||
explicit Edge(Block *SrcBlock, Block *DstBlock, uint64_t EC)
|
||||
: SrcChain(SrcBlock->CurChain), DstChain(DstBlock->CurChain),
|
||||
Jumps(1, std::make_pair(std::make_pair(SrcBlock, DstBlock), EC)) {}
|
||||
|
||||
const JumpList &jumps() const { return Jumps; }
|
||||
|
||||
void changeEndpoint(Chain *From, Chain *To) {
|
||||
if (From == SrcChain)
|
||||
SrcChain = To;
|
||||
if (From == DstChain)
|
||||
DstChain = To;
|
||||
}
|
||||
|
||||
void appendJump(Block *SrcBlock, Block *DstBlock, uint64_t EC) {
|
||||
Jumps.emplace_back(std::make_pair(SrcBlock, DstBlock), EC);
|
||||
}
|
||||
|
||||
void moveJumps(Edge *Other) {
|
||||
Jumps.insert(Jumps.end(), Other->Jumps.begin(), Other->Jumps.end());
|
||||
Other->Jumps.clear();
|
||||
}
|
||||
|
||||
bool hasCachedMergeGain(Chain *Src, Chain *Dst) const {
|
||||
return Src == SrcChain ? CacheValidForward : CacheValidBackward;
|
||||
}
|
||||
|
||||
MergeGainTy getCachedMergeGain(Chain *Src, Chain *Dst) const {
|
||||
return Src == SrcChain ? CachedGainForward : CachedGainBackward;
|
||||
}
|
||||
|
||||
void setCachedMergeGain(Chain *Src, Chain *Dst, MergeGainTy MergeGain) {
|
||||
if (Src == SrcChain) {
|
||||
CachedGainForward = MergeGain;
|
||||
CacheValidForward = true;
|
||||
} else {
|
||||
CachedGainBackward = MergeGain;
|
||||
CacheValidBackward = true;
|
||||
}
|
||||
}
|
||||
|
||||
void invalidateCache() {
|
||||
CacheValidForward = false;
|
||||
CacheValidBackward = false;
|
||||
}
|
||||
|
||||
private:
|
||||
Chain *SrcChain{nullptr};
|
||||
Chain *DstChain{nullptr};
|
||||
// Original jumps in the binary with correspinding execution counts
|
||||
JumpList Jumps;
|
||||
// Cached ext-tsp value for merging the pair of chains
|
||||
// Since the gain of merging (Src, Dst) and (Dst, Src) might be different,
|
||||
// we store both values here
|
||||
MergeGainTy CachedGainForward;
|
||||
MergeGainTy CachedGainBackward;
|
||||
// Whether the cached value must be recomputed
|
||||
bool CacheValidForward{false};
|
||||
bool CacheValidBackward{false};
|
||||
};
|
||||
|
||||
void Chain::mergeEdges(Chain *Other) {
|
||||
assert(this != Other && "cannot merge a chain with itself");
|
||||
|
||||
// Update edges adjacent to chain Other
|
||||
for (auto EdgeIt : Other->Edges) {
|
||||
Chain *const DstChain = EdgeIt.first;
|
||||
Edge *const DstEdge = EdgeIt.second;
|
||||
Chain *const TargetChain = DstChain == Other ? this : DstChain;
|
||||
|
||||
// Find the corresponding edge in the current chain
|
||||
Edge *curEdge = getEdge(TargetChain);
|
||||
if (curEdge == nullptr) {
|
||||
DstEdge->changeEndpoint(Other, this);
|
||||
this->addEdge(TargetChain, DstEdge);
|
||||
if (DstChain != this && DstChain != Other)
|
||||
DstChain->addEdge(this, DstEdge);
|
||||
} else {
|
||||
curEdge->moveJumps(DstEdge);
|
||||
}
|
||||
// Cleanup leftover edge
|
||||
if (DstChain != Other)
|
||||
DstChain->removeEdge(Other);
|
||||
}
|
||||
}
|
||||
|
||||
// A wrapper around three chains of basic blocks; it is used to avoid extra
|
||||
// instantiation of the vectors.
|
||||
class MergedChain {
|
||||
public:
|
||||
MergedChain(BlockIter Begin1, BlockIter End1, BlockIter Begin2 = BlockIter(),
|
||||
BlockIter End2 = BlockIter(), BlockIter Begin3 = BlockIter(),
|
||||
BlockIter End3 = BlockIter())
|
||||
: Begin1(Begin1), End1(End1), Begin2(Begin2), End2(End2), Begin3(Begin3),
|
||||
End3(End3) {}
|
||||
|
||||
template <typename F> void forEach(const F &Func) const {
|
||||
for (auto It = Begin1; It != End1; It++)
|
||||
Func(*It);
|
||||
for (auto It = Begin2; It != End2; It++)
|
||||
Func(*It);
|
||||
for (auto It = Begin3; It != End3; It++)
|
||||
Func(*It);
|
||||
}
|
||||
|
||||
std::vector<Block *> getBlocks() const {
|
||||
std::vector<Block *> Result;
|
||||
Result.reserve(std::distance(Begin1, End1) + std::distance(Begin2, End2) +
|
||||
std::distance(Begin3, End3));
|
||||
Result.insert(Result.end(), Begin1, End1);
|
||||
Result.insert(Result.end(), Begin2, End2);
|
||||
Result.insert(Result.end(), Begin3, End3);
|
||||
return Result;
|
||||
}
|
||||
|
||||
const Block *getFirstBlock() const { return *Begin1; }
|
||||
|
||||
private:
|
||||
BlockIter Begin1;
|
||||
BlockIter End1;
|
||||
BlockIter Begin2;
|
||||
BlockIter End2;
|
||||
BlockIter Begin3;
|
||||
BlockIter End3;
|
||||
};
|
||||
|
||||
/// Deterministically compare pairs of chains
|
||||
bool compareChainPairs(const Chain *A1, const Chain *B1, const Chain *A2,
|
||||
const Chain *B2) {
|
||||
const uint64_t Samples1 = A1->executionCount() + B1->executionCount();
|
||||
const uint64_t Samples2 = A2->executionCount() + B2->executionCount();
|
||||
if (Samples1 != Samples2)
|
||||
return Samples1 < Samples2;
|
||||
|
||||
// Making the order deterministic
|
||||
if (A1 != A2)
|
||||
return A1->id() < A2->id();
|
||||
return B1->id() < B2->id();
|
||||
}
|
||||
class ExtTSP {
|
||||
public:
|
||||
ExtTSP(BinaryFunction &BF) : BF(BF) { initialize(); }
|
||||
|
||||
/// Run the algorithm and return an ordering of basic block
|
||||
void run(BinaryFunction::BasicBlockOrderType &Order) {
|
||||
// Pass 1: Merge blocks with their fallthrough successors
|
||||
mergeFallthroughs();
|
||||
|
||||
// Pass 2: Merge pairs of chains while improving the ExtTSP objective
|
||||
mergeChainPairs();
|
||||
|
||||
// Pass 3: Merge cold blocks to reduce code size
|
||||
mergeColdChains();
|
||||
|
||||
// Collect blocks from all chains
|
||||
concatChains(Order);
|
||||
}
|
||||
|
||||
private:
|
||||
/// Initialize algorithm's data structures
|
||||
void initialize() {
|
||||
// Create a separate MCCodeEmitter to allow lock-free execution
|
||||
BinaryContext::IndependentCodeEmitter Emitter;
|
||||
if (!opts::NoThreads)
|
||||
Emitter = BF.getBinaryContext().createIndependentMCCodeEmitter();
|
||||
|
||||
// Initialize CFG nodes
|
||||
AllBlocks.reserve(BF.getLayout().block_size());
|
||||
size_t LayoutIndex = 0;
|
||||
for (BinaryBasicBlock *BB : BF.getLayout().blocks()) {
|
||||
BB->setLayoutIndex(LayoutIndex++);
|
||||
uint64_t Size =
|
||||
std::max<uint64_t>(BB->estimateSize(Emitter.MCE.get()), 1);
|
||||
AllBlocks.emplace_back(BB, Size);
|
||||
}
|
||||
|
||||
// Initialize edges for the blocks and compute their total in/out weights
|
||||
size_t NumEdges = 0;
|
||||
for (Block &Block : AllBlocks) {
|
||||
auto BI = Block.BB->branch_info_begin();
|
||||
for (BinaryBasicBlock *SuccBB : Block.BB->successors()) {
|
||||
assert(BI->Count != BinaryBasicBlock::COUNT_NO_PROFILE &&
|
||||
"missing profile for a jump");
|
||||
if (SuccBB != Block.BB && BI->Count > 0) {
|
||||
class Block &SuccBlock = AllBlocks[SuccBB->getLayoutIndex()];
|
||||
uint64_t Count = BI->Count;
|
||||
SuccBlock.InWeight += Count;
|
||||
SuccBlock.InJumps.emplace_back(&Block, Count);
|
||||
Block.OutWeight += Count;
|
||||
Block.OutJumps.emplace_back(&SuccBlock, Count);
|
||||
NumEdges++;
|
||||
}
|
||||
++BI;
|
||||
}
|
||||
}
|
||||
|
||||
// Initialize execution count for every basic block, which is the
|
||||
// maximum over the sums of all in and out edge weights.
|
||||
// Also execution count of the entry point is set to at least 1
|
||||
for (Block &Block : AllBlocks) {
|
||||
size_t Index = Block.Index;
|
||||
Block.ExecutionCount = std::max(Block.ExecutionCount, Block.InWeight);
|
||||
Block.ExecutionCount = std::max(Block.ExecutionCount, Block.OutWeight);
|
||||
if (Index == 0 && Block.ExecutionCount == 0)
|
||||
Block.ExecutionCount = 1;
|
||||
}
|
||||
|
||||
// Initialize chains
|
||||
AllChains.reserve(BF.getLayout().block_size());
|
||||
HotChains.reserve(BF.getLayout().block_size());
|
||||
for (Block &Block : AllBlocks) {
|
||||
AllChains.emplace_back(Block.Index, &Block);
|
||||
Block.CurChain = &AllChains.back();
|
||||
if (Block.ExecutionCount > 0)
|
||||
HotChains.push_back(&AllChains.back());
|
||||
}
|
||||
|
||||
// Initialize edges
|
||||
AllEdges.reserve(NumEdges);
|
||||
for (Block &Block : AllBlocks) {
|
||||
for (std::pair<class Block *, uint64_t> &Jump : Block.OutJumps) {
|
||||
class Block *const SuccBlock = Jump.first;
|
||||
Edge *CurEdge = Block.CurChain->getEdge(SuccBlock->CurChain);
|
||||
// this edge is already present in the graph
|
||||
if (CurEdge != nullptr) {
|
||||
assert(SuccBlock->CurChain->getEdge(Block.CurChain) != nullptr);
|
||||
CurEdge->appendJump(&Block, SuccBlock, Jump.second);
|
||||
continue;
|
||||
}
|
||||
// this is a new edge
|
||||
AllEdges.emplace_back(&Block, SuccBlock, Jump.second);
|
||||
Block.CurChain->addEdge(SuccBlock->CurChain, &AllEdges.back());
|
||||
SuccBlock->CurChain->addEdge(Block.CurChain, &AllEdges.back());
|
||||
}
|
||||
}
|
||||
assert(AllEdges.size() <= NumEdges && "Incorrect number of created edges");
|
||||
}
|
||||
|
||||
/// For a pair of blocks, A and B, block B is the fallthrough successor of A,
|
||||
/// if (i) all jumps (based on profile) from A goes to B and (ii) all jumps
|
||||
/// to B are from A. Such blocks should be adjacent in an optimal ordering;
|
||||
/// the method finds and merges such pairs of blocks
|
||||
void mergeFallthroughs() {
|
||||
// Find fallthroughs based on edge weights
|
||||
for (Block &Block : AllBlocks) {
|
||||
if (Block.BB->succ_size() == 1 &&
|
||||
Block.BB->getSuccessor()->pred_size() == 1 &&
|
||||
Block.BB->getSuccessor()->getLayoutIndex() != 0) {
|
||||
size_t SuccIndex = Block.BB->getSuccessor()->getLayoutIndex();
|
||||
Block.FallthroughSucc = &AllBlocks[SuccIndex];
|
||||
AllBlocks[SuccIndex].FallthroughPred = &Block;
|
||||
continue;
|
||||
}
|
||||
|
||||
if (Block.OutWeight == 0)
|
||||
continue;
|
||||
for (std::pair<class Block *, uint64_t> &Edge : Block.OutJumps) {
|
||||
class Block *const SuccBlock = Edge.first;
|
||||
// Successor cannot be the first BB, which is pinned
|
||||
if (Block.OutWeight == Edge.second &&
|
||||
SuccBlock->InWeight == Edge.second && SuccBlock->Index != 0) {
|
||||
Block.FallthroughSucc = SuccBlock;
|
||||
SuccBlock->FallthroughPred = &Block;
|
||||
break;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// There might be 'cycles' in the fallthrough dependencies (since profile
|
||||
// data isn't 100% accurate).
|
||||
// Break the cycles by choosing the block with smallest index as the tail
|
||||
for (Block &Block : AllBlocks) {
|
||||
if (Block.FallthroughSucc == nullptr || Block.FallthroughPred == nullptr)
|
||||
continue;
|
||||
|
||||
class Block *SuccBlock = Block.FallthroughSucc;
|
||||
while (SuccBlock != nullptr && SuccBlock != &Block)
|
||||
SuccBlock = SuccBlock->FallthroughSucc;
|
||||
|
||||
if (SuccBlock == nullptr)
|
||||
continue;
|
||||
// break the cycle
|
||||
AllBlocks[Block.FallthroughPred->Index].FallthroughSucc = nullptr;
|
||||
Block.FallthroughPred = nullptr;
|
||||
}
|
||||
|
||||
// Merge blocks with their fallthrough successors
|
||||
for (Block &Block : AllBlocks) {
|
||||
if (Block.FallthroughPred == nullptr &&
|
||||
Block.FallthroughSucc != nullptr) {
|
||||
class Block *CurBlock = &Block;
|
||||
while (CurBlock->FallthroughSucc != nullptr) {
|
||||
class Block *const NextBlock = CurBlock->FallthroughSucc;
|
||||
mergeChains(Block.CurChain, NextBlock->CurChain, 0, MergeTypeTy::X_Y);
|
||||
CurBlock = NextBlock;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/// Merge pairs of chains while improving the ExtTSP objective
|
||||
void mergeChainPairs() {
|
||||
while (HotChains.size() > 1) {
|
||||
Chain *BestChainPred = nullptr;
|
||||
Chain *BestChainSucc = nullptr;
|
||||
auto BestGain = MergeGainTy();
|
||||
// Iterate over all pairs of chains
|
||||
for (Chain *ChainPred : HotChains) {
|
||||
// Get candidates for merging with the current chain
|
||||
for (auto EdgeIter : ChainPred->edges()) {
|
||||
Chain *ChainSucc = EdgeIter.first;
|
||||
Edge *ChainEdge = EdgeIter.second;
|
||||
// Ignore loop edges
|
||||
if (ChainPred == ChainSucc)
|
||||
continue;
|
||||
|
||||
// Compute the gain of merging the two chains
|
||||
MergeGainTy CurGain = mergeGain(ChainPred, ChainSucc, ChainEdge);
|
||||
if (CurGain.score() <= EPS)
|
||||
continue;
|
||||
|
||||
if (BestGain < CurGain ||
|
||||
(std::abs(CurGain.score() - BestGain.score()) < EPS &&
|
||||
compareChainPairs(ChainPred, ChainSucc, BestChainPred,
|
||||
BestChainSucc))) {
|
||||
BestGain = CurGain;
|
||||
BestChainPred = ChainPred;
|
||||
BestChainSucc = ChainSucc;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Stop merging when there is no improvement
|
||||
if (BestGain.score() <= EPS)
|
||||
break;
|
||||
|
||||
// Merge the best pair of chains
|
||||
mergeChains(BestChainPred, BestChainSucc, BestGain.mergeOffset(),
|
||||
BestGain.mergeType());
|
||||
}
|
||||
}
|
||||
|
||||
/// Merge remaining blocks into chains w/o taking jump counts into
|
||||
/// consideration. This allows to maintain the original block order in the
|
||||
/// absense of profile data
|
||||
void mergeColdChains() {
|
||||
for (BinaryBasicBlock *SrcBB : BF.getLayout().blocks()) {
|
||||
// Iterating in reverse order to make sure original fallthrough jumps are
|
||||
// merged first; this might be beneficial for code size.
|
||||
for (auto Itr = SrcBB->succ_rbegin(); Itr != SrcBB->succ_rend(); ++Itr) {
|
||||
BinaryBasicBlock *DstBB = *Itr;
|
||||
size_t SrcIndex = SrcBB->getLayoutIndex();
|
||||
size_t DstIndex = DstBB->getLayoutIndex();
|
||||
Chain *SrcChain = AllBlocks[SrcIndex].CurChain;
|
||||
Chain *DstChain = AllBlocks[DstIndex].CurChain;
|
||||
bool IsColdSrc = SrcChain->executionCount() == 0;
|
||||
bool IsColdDst = DstChain->executionCount() == 0;
|
||||
if (SrcChain != DstChain && !DstChain->isEntryPoint() &&
|
||||
SrcChain->blocks().back()->Index == SrcIndex &&
|
||||
DstChain->blocks().front()->Index == DstIndex &&
|
||||
IsColdSrc == IsColdDst)
|
||||
mergeChains(SrcChain, DstChain, 0, MergeTypeTy::X_Y);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/// Compute ExtTSP score for a given order of basic blocks
|
||||
double score(const MergedChain &MergedBlocks, const JumpList &Jumps) const {
|
||||
if (Jumps.empty())
|
||||
return 0.0;
|
||||
uint64_t CurAddr = 0;
|
||||
MergedBlocks.forEach(
|
||||
[&](const Block *BB) {
|
||||
BB->EstimatedAddr = CurAddr;
|
||||
CurAddr += BB->Size;
|
||||
}
|
||||
);
|
||||
|
||||
double Score = 0;
|
||||
for (const std::pair<std::pair<Block *, Block *>, uint64_t> &Jump : Jumps) {
|
||||
const Block *SrcBlock = Jump.first.first;
|
||||
const Block *DstBlock = Jump.first.second;
|
||||
Score += extTSPScore(SrcBlock->EstimatedAddr, SrcBlock->Size,
|
||||
DstBlock->EstimatedAddr, Jump.second);
|
||||
}
|
||||
return Score;
|
||||
}
|
||||
|
||||
/// Compute the gain of merging two chains
|
||||
///
|
||||
/// The function considers all possible ways of merging two chains and
|
||||
/// computes the one having the largest increase in ExtTSP objective. The
|
||||
/// result is a pair with the first element being the gain and the second
|
||||
/// element being the corresponding merging type.
|
||||
MergeGainTy mergeGain(Chain *ChainPred, Chain *ChainSucc, Edge *Edge) const {
|
||||
if (Edge->hasCachedMergeGain(ChainPred, ChainSucc))
|
||||
return Edge->getCachedMergeGain(ChainPred, ChainSucc);
|
||||
|
||||
// Precompute jumps between ChainPred and ChainSucc
|
||||
JumpList Jumps = Edge->jumps();
|
||||
class Edge *EdgePP = ChainPred->getEdge(ChainPred);
|
||||
if (EdgePP != nullptr)
|
||||
Jumps.insert(Jumps.end(), EdgePP->jumps().begin(), EdgePP->jumps().end());
|
||||
assert(Jumps.size() > 0 && "trying to merge chains w/o jumps");
|
||||
|
||||
MergeGainTy Gain = MergeGainTy();
|
||||
// Try to concatenate two chains w/o splitting
|
||||
Gain = computeMergeGain(Gain, ChainPred, ChainSucc, Jumps, 0,
|
||||
MergeTypeTy::X_Y);
|
||||
|
||||
// Try to break ChainPred in various ways and concatenate with ChainSucc
|
||||
if (ChainPred->blocks().size() <= opts::ChainSplitThreshold) {
|
||||
for (size_t Offset = 1; Offset < ChainPred->blocks().size(); Offset++) {
|
||||
Block *BB1 = ChainPred->blocks()[Offset - 1];
|
||||
Block *BB2 = ChainPred->blocks()[Offset];
|
||||
// Does the splitting break FT successors?
|
||||
if (BB1->FallthroughSucc != nullptr) {
|
||||
(void)BB2;
|
||||
assert(BB1->FallthroughSucc == BB2 && "Fallthrough not preserved");
|
||||
continue;
|
||||
}
|
||||
|
||||
Gain = computeMergeGain(Gain, ChainPred, ChainSucc, Jumps, Offset,
|
||||
MergeTypeTy::X1_Y_X2);
|
||||
Gain = computeMergeGain(Gain, ChainPred, ChainSucc, Jumps, Offset,
|
||||
MergeTypeTy::Y_X2_X1);
|
||||
Gain = computeMergeGain(Gain, ChainPred, ChainSucc, Jumps, Offset,
|
||||
MergeTypeTy::X2_X1_Y);
|
||||
}
|
||||
}
|
||||
|
||||
Edge->setCachedMergeGain(ChainPred, ChainSucc, Gain);
|
||||
return Gain;
|
||||
}
|
||||
|
||||
/// Merge two chains and update the best Gain
|
||||
MergeGainTy computeMergeGain(const MergeGainTy &CurGain,
|
||||
const Chain *ChainPred, const Chain *ChainSucc,
|
||||
const JumpList &Jumps, size_t MergeOffset,
|
||||
MergeTypeTy MergeType) const {
|
||||
MergedChain MergedBlocks = mergeBlocks(
|
||||
ChainPred->blocks(), ChainSucc->blocks(), MergeOffset, MergeType);
|
||||
|
||||
// Do not allow a merge that does not preserve the original entry block
|
||||
if ((ChainPred->isEntryPoint() || ChainSucc->isEntryPoint()) &&
|
||||
MergedBlocks.getFirstBlock()->Index != 0)
|
||||
return CurGain;
|
||||
|
||||
// The gain for the new chain
|
||||
const double NewScore = score(MergedBlocks, Jumps) - ChainPred->score();
|
||||
auto NewGain = MergeGainTy(NewScore, MergeOffset, MergeType);
|
||||
return CurGain < NewGain ? NewGain : CurGain;
|
||||
}
|
||||
|
||||
/// Merge two chains of blocks respecting a given merge 'type' and 'offset'
|
||||
///
|
||||
/// If MergeType == 0, then the result is a concatentation of two chains.
|
||||
/// Otherwise, the first chain is cut into two sub-chains at the offset,
|
||||
/// and merged using all possible ways of concatenating three chains.
|
||||
MergedChain mergeBlocks(const std::vector<Block *> &X,
|
||||
const std::vector<Block *> &Y, size_t MergeOffset,
|
||||
MergeTypeTy MergeType) const {
|
||||
// Split the first chain, X, into X1 and X2
|
||||
BlockIter BeginX1 = X.begin();
|
||||
BlockIter EndX1 = X.begin() + MergeOffset;
|
||||
BlockIter BeginX2 = X.begin() + MergeOffset;
|
||||
BlockIter EndX2 = X.end();
|
||||
BlockIter BeginY = Y.begin();
|
||||
BlockIter EndY = Y.end();
|
||||
|
||||
// Construct a new chain from the three existing ones
|
||||
switch (MergeType) {
|
||||
case MergeTypeTy::X_Y:
|
||||
return MergedChain(BeginX1, EndX2, BeginY, EndY);
|
||||
case MergeTypeTy::X1_Y_X2:
|
||||
return MergedChain(BeginX1, EndX1, BeginY, EndY, BeginX2, EndX2);
|
||||
case MergeTypeTy::Y_X2_X1:
|
||||
return MergedChain(BeginY, EndY, BeginX2, EndX2, BeginX1, EndX1);
|
||||
case MergeTypeTy::X2_X1_Y:
|
||||
return MergedChain(BeginX2, EndX2, BeginX1, EndX1, BeginY, EndY);
|
||||
}
|
||||
|
||||
llvm_unreachable("unexpected merge type");
|
||||
}
|
||||
|
||||
/// Merge chain From into chain Into, update the list of active chains,
|
||||
/// adjacency information, and the corresponding cached values
|
||||
void mergeChains(Chain *Into, Chain *From, size_t MergeOffset,
|
||||
MergeTypeTy MergeType) {
|
||||
assert(Into != From && "a chain cannot be merged with itself");
|
||||
|
||||
// Merge the blocks
|
||||
MergedChain MergedBlocks =
|
||||
mergeBlocks(Into->blocks(), From->blocks(), MergeOffset, MergeType);
|
||||
Into->merge(From, MergedBlocks.getBlocks());
|
||||
Into->mergeEdges(From);
|
||||
From->clear();
|
||||
|
||||
// Update cached ext-tsp score for the new chain
|
||||
Edge *SelfEdge = Into->getEdge(Into);
|
||||
if (SelfEdge != nullptr) {
|
||||
MergedBlocks = MergedChain(Into->blocks().begin(), Into->blocks().end());
|
||||
Into->setScore(score(MergedBlocks, SelfEdge->jumps()));
|
||||
}
|
||||
|
||||
// Remove chain From from the list of active chains
|
||||
llvm::erase_value(HotChains, From);
|
||||
|
||||
// Invalidate caches
|
||||
for (std::pair<Chain *, Edge *> EdgeIter : Into->edges())
|
||||
EdgeIter.second->invalidateCache();
|
||||
}
|
||||
|
||||
/// Concatenate all chains into a final order
|
||||
void concatChains(BinaryFunction::BasicBlockOrderType &Order) {
|
||||
// Collect chains
|
||||
std::vector<Chain *> SortedChains;
|
||||
for (Chain &Chain : AllChains)
|
||||
if (Chain.blocks().size() > 0)
|
||||
SortedChains.push_back(&Chain);
|
||||
|
||||
// Sorting chains by density in decreasing order
|
||||
llvm::stable_sort(SortedChains, [](const Chain *C1, const Chain *C2) {
|
||||
// Original entry point to the front
|
||||
if (C1->isEntryPoint() != C2->isEntryPoint()) {
|
||||
if (C1->isEntryPoint())
|
||||
return true;
|
||||
if (C2->isEntryPoint())
|
||||
return false;
|
||||
}
|
||||
|
||||
const double D1 = C1->density();
|
||||
const double D2 = C2->density();
|
||||
if (D1 != D2)
|
||||
return D1 > D2;
|
||||
|
||||
// Making the order deterministic
|
||||
return C1->id() < C2->id();
|
||||
});
|
||||
|
||||
// Collect the basic blocks in the order specified by their chains
|
||||
Order.reserve(BF.getLayout().block_size());
|
||||
for (Chain *Chain : SortedChains)
|
||||
for (Block *Block : Chain->blocks())
|
||||
Order.push_back(Block->BB);
|
||||
}
|
||||
|
||||
private:
|
||||
// The binary function
|
||||
BinaryFunction &BF;
|
||||
|
||||
// All CFG nodes (basic blocks)
|
||||
std::vector<Block> AllBlocks;
|
||||
|
||||
// All chains of blocks
|
||||
std::vector<Chain> AllChains;
|
||||
|
||||
// Active chains. The vector gets updated at runtime when chains are merged
|
||||
std::vector<Chain *> HotChains;
|
||||
|
||||
// All edges between chains
|
||||
std::vector<Edge> AllEdges;
|
||||
};
|
||||
|
||||
void ExtTSPReorderAlgorithm::reorderBasicBlocks(BinaryFunction &BF,
|
||||
BasicBlockOrder &Order) const {
|
||||
if (BF.getLayout().block_empty())
|
||||
return;
|
||||
|
||||
// Do not change layout of functions w/o profile information
|
||||
if (!BF.hasValidProfile() || BF.getLayout().block_size() <= 2) {
|
||||
for (BinaryBasicBlock *BB : BF.getLayout().blocks())
|
||||
Order.push_back(BB);
|
||||
return;
|
||||
}
|
||||
|
||||
// Apply the algorithm
|
||||
ExtTSP(BF).run(Order);
|
||||
|
||||
// Verify correctness
|
||||
assert(Order[0]->isEntryPoint() && "Original entry point is not preserved");
|
||||
assert(Order.size() == BF.getLayout().block_size() &&
|
||||
"Wrong size of reordered layout");
|
||||
}
|
||||
|
||||
} // namespace bolt
|
||||
} // namespace llvm
|
||||
@ -15,6 +15,7 @@
|
||||
#include "bolt/Core/BinaryBasicBlock.h"
|
||||
#include "bolt/Core/BinaryFunction.h"
|
||||
#include "llvm/Support/CommandLine.h"
|
||||
#include "llvm/Transforms/Utils/CodeLayout.h"
|
||||
#include <queue>
|
||||
#include <random>
|
||||
#include <stack>
|
||||
@ -500,6 +501,56 @@ void TSPReorderAlgorithm::reorderBasicBlocks(BinaryFunction &BF,
|
||||
Order.push_back(BB);
|
||||
}
|
||||
|
||||
void ExtTSPReorderAlgorithm::reorderBasicBlocks(BinaryFunction &BF,
|
||||
BasicBlockOrder &Order) const {
|
||||
if (BF.getLayout().block_empty())
|
||||
return;
|
||||
|
||||
// Do not change layout of functions w/o profile information
|
||||
if (!BF.hasValidProfile() || BF.getLayout().block_size() <= 2) {
|
||||
for (BinaryBasicBlock *BB : BF.getLayout().blocks())
|
||||
Order.push_back(BB);
|
||||
return;
|
||||
}
|
||||
|
||||
// Create a separate MCCodeEmitter to allow lock-free execution
|
||||
BinaryContext::IndependentCodeEmitter Emitter;
|
||||
if (!opts::NoThreads)
|
||||
Emitter = BF.getBinaryContext().createIndependentMCCodeEmitter();
|
||||
|
||||
// Initialize CFG nodes and their data
|
||||
std::vector<uint64_t> BlockSizes;
|
||||
std::vector<uint64_t> BlockCounts;
|
||||
BasicBlockOrder OrigOrder;
|
||||
BF.getLayout().updateLayoutIndices();
|
||||
for (BinaryBasicBlock *BB : BF.getLayout().blocks()) {
|
||||
uint64_t Size = std::max<uint64_t>(BB->estimateSize(Emitter.MCE.get()), 1);
|
||||
BlockSizes.push_back(Size);
|
||||
BlockCounts.push_back(BB->getKnownExecutionCount());
|
||||
OrigOrder.push_back(BB);
|
||||
}
|
||||
|
||||
// Initialize CFG edges
|
||||
using JumpT = std::pair<uint64_t, uint64_t>;
|
||||
std::vector<std::pair<JumpT, uint64_t>> JumpCounts;
|
||||
for (BinaryBasicBlock *BB : BF.getLayout().blocks()) {
|
||||
auto BI = BB->branch_info_begin();
|
||||
for (BinaryBasicBlock *SuccBB : BB->successors()) {
|
||||
assert(BI->Count != BinaryBasicBlock::COUNT_NO_PROFILE &&
|
||||
"missing profile for a jump");
|
||||
auto It = std::make_pair(BB->getLayoutIndex(), SuccBB->getLayoutIndex());
|
||||
JumpCounts.push_back(std::make_pair(It, BI->Count));
|
||||
++BI;
|
||||
}
|
||||
}
|
||||
|
||||
// Run the layout algorithm
|
||||
auto Result = applyExtTspLayout(BlockSizes, BlockCounts, JumpCounts);
|
||||
Order.reserve(BF.getLayout().block_size());
|
||||
for (uint64_t R : Result)
|
||||
Order.push_back(OrigOrder[R]);
|
||||
}
|
||||
|
||||
void OptimizeReorderAlgorithm::reorderBasicBlocks(
|
||||
BinaryFunction &BF, BasicBlockOrder &Order) const {
|
||||
if (BF.getLayout().block_empty())
|
||||
|
||||
Loading…
Reference in New Issue
Block a user