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CaptureTracking becomes very expensive in large basic blocks while calling PointerMayBeCaptured. PointerMayBeCaptured scans the BB the number of times equal to the number of uses of 'BeforeHere', which is currently capped at 20 and bails out with Tracker->tooManyUses(). The bottleneck here is the number of calls to PointerMayBeCaptured * the basic block scan. In a testcase with a 82k instruction BB, PointerMayBeCaptured is called 130k times, leading to 'shouldExplore' taking 527k runs, this currently takes ~12min. To fix this we locally (within PointerMayBeCaptured) number the instructions in the basic block using a DenseMap to cache instruction positions/numbers. We build the cache incrementally every time we need to scan an unexplored part of the BB, improving compile time to only take ~2min. This triggers in the flow: DeadStoreElimination -> MepDepAnalysis -> CaptureTracking. Side note: after multiple runs in the test-suite I've seen no performance nor compile time regressions, but could note a couple of compile time improvements: Performance Improvements - Compile Time Delta Previous Current StdDev SingleSource/Benchmarks/Misc-C++/bigfib -4.48% 0.8547 0.8164 0.0022 MultiSource/Benchmarks/TSVC/LoopRerolling-dbl/LoopRerolling-dbl -1.47% 1.3912 1.3707 0.0056 Differential Revision: http://reviews.llvm.org/D7010 llvm-svn: 240560
95 lines
4.0 KiB
C++
95 lines
4.0 KiB
C++
//===-- Analysis/CFG.h - BasicBlock Analyses --------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This family of functions performs analyses on basic blocks, and instructions
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// contained within basic blocks.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_CFG_H
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#define LLVM_ANALYSIS_CFG_H
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CFG.h"
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namespace llvm {
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class BasicBlock;
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class DominatorTree;
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class Function;
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class Instruction;
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class LoopInfo;
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class TerminatorInst;
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/// Analyze the specified function to find all of the loop backedges in the
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/// function and return them. This is a relatively cheap (compared to
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/// computing dominators and loop info) analysis.
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///
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/// The output is added to Result, as pairs of <from,to> edge info.
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void FindFunctionBackedges(
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const Function &F,
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SmallVectorImpl<std::pair<const BasicBlock *, const BasicBlock *> > &
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Result);
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/// Search for the specified successor of basic block BB and return its position
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/// in the terminator instruction's list of successors. It is an error to call
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/// this with a block that is not a successor.
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unsigned GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ);
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/// Return true if the specified edge is a critical edge. Critical edges are
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/// edges from a block with multiple successors to a block with multiple
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/// predecessors.
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///
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bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
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bool AllowIdenticalEdges = false);
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/// \brief Determine whether instruction 'To' is reachable from 'From',
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/// returning true if uncertain.
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///
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/// Determine whether there is a path from From to To within a single function.
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/// Returns false only if we can prove that once 'From' has been executed then
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/// 'To' can not be executed. Conservatively returns true.
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///
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/// This function is linear with respect to the number of blocks in the CFG,
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/// walking down successors from From to reach To, with a fixed threshold.
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/// Using DT or LI allows us to answer more quickly. LI reduces the cost of
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/// an entire loop of any number of blocsk to be the same as the cost of a
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/// single block. DT reduces the cost by allowing the search to terminate when
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/// we find a block that dominates the block containing 'To'. DT is most useful
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/// on branchy code but not loops, and LI is most useful on code with loops but
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/// does not help on branchy code outside loops.
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bool isPotentiallyReachable(const Instruction *From, const Instruction *To,
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const DominatorTree *DT = nullptr,
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const LoopInfo *LI = nullptr);
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/// \brief Determine whether block 'To' is reachable from 'From', returning
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/// true if uncertain.
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///
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/// Determine whether there is a path from From to To within a single function.
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/// Returns false only if we can prove that once 'From' has been reached then
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/// 'To' can not be executed. Conservatively returns true.
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bool isPotentiallyReachable(const BasicBlock *From, const BasicBlock *To,
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const DominatorTree *DT = nullptr,
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const LoopInfo *LI = nullptr);
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/// \brief Determine whether there is at least one path from a block in
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/// 'Worklist' to 'StopBB', returning true if uncertain.
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///
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/// Determine whether there is a path from at least one block in Worklist to
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/// StopBB within a single function. Returns false only if we can prove that
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/// once any block in 'Worklist' has been reached then 'StopBB' can not be
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/// executed. Conservatively returns true.
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bool isPotentiallyReachableFromMany(SmallVectorImpl<BasicBlock *> &Worklist,
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BasicBlock *StopBB,
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const DominatorTree *DT = nullptr,
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const LoopInfo *LI = nullptr);
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} // End llvm namespace
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#endif
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