LCOV - code coverage report
Current view: top level - lib/Analysis - CFG.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 65 65 100.0 %
Date: 2018-10-20 13:21:21 Functions: 8 8 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===-- CFG.cpp - BasicBlock analysis --------------------------------------==//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This family of functions performs analyses on basic blocks, and instructions
      11             : // contained within basic blocks.
      12             : //
      13             : //===----------------------------------------------------------------------===//
      14             : 
      15             : #include "llvm/Analysis/CFG.h"
      16             : #include "llvm/ADT/SmallSet.h"
      17             : #include "llvm/Analysis/LoopInfo.h"
      18             : #include "llvm/IR/Dominators.h"
      19             : 
      20             : using namespace llvm;
      21             : 
      22             : /// FindFunctionBackedges - Analyze the specified function to find all of the
      23             : /// loop backedges in the function and return them.  This is a relatively cheap
      24             : /// (compared to computing dominators and loop info) analysis.
      25             : ///
      26             : /// The output is added to Result, as pairs of <from,to> edge info.
      27      403975 : void llvm::FindFunctionBackedges(const Function &F,
      28             :      SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
      29             :   const BasicBlock *BB = &F.getEntryBlock();
      30      403976 :   if (succ_empty(BB))
      31      269695 :     return;
      32             : 
      33             :   SmallPtrSet<const BasicBlock*, 8> Visited;
      34             :   SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
      35             :   SmallPtrSet<const BasicBlock*, 8> InStack;
      36             : 
      37      134281 :   Visited.insert(BB);
      38      134281 :   VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
      39      134281 :   InStack.insert(BB);
      40             :   do {
      41             :     std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
      42     4294281 :     const BasicBlock *ParentBB = Top.first;
      43             :     succ_const_iterator &I = Top.second;
      44             : 
      45             :     bool FoundNew = false;
      46     5043819 :     while (I != succ_end(ParentBB)) {
      47             :       BB = *I++;
      48     2829538 :       if (Visited.insert(BB).second) {
      49             :         FoundNew = true;
      50             :         break;
      51             :       }
      52             :       // Successor is in VisitStack, it's a back edge.
      53      749538 :       if (InStack.count(BB))
      54       45156 :         Result.push_back(std::make_pair(ParentBB, BB));
      55             :     }
      56             : 
      57     4294281 :     if (FoundNew) {
      58             :       // Go down one level if there is a unvisited successor.
      59     2080000 :       InStack.insert(BB);
      60     2080000 :       VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
      61             :     } else {
      62             :       // Go up one level.
      63             :       InStack.erase(VisitStack.pop_back_val().first);
      64             :     }
      65     4294281 :   } while (!VisitStack.empty());
      66             : }
      67             : 
      68             : /// GetSuccessorNumber - Search for the specified successor of basic block BB
      69             : /// and return its position in the terminator instruction's list of
      70             : /// successors.  It is an error to call this with a block that is not a
      71             : /// successor.
      72        3775 : unsigned llvm::GetSuccessorNumber(const BasicBlock *BB,
      73             :     const BasicBlock *Succ) {
      74        3775 :   const Instruction *Term = BB->getTerminator();
      75             : #ifndef NDEBUG
      76             :   unsigned e = Term->getNumSuccessors();
      77             : #endif
      78         682 :   for (unsigned i = 0; ; ++i) {
      79         682 :     assert(i != e && "Didn't find edge?");
      80        4457 :     if (Term->getSuccessor(i) == Succ)
      81        3775 :       return i;
      82             :   }
      83             : }
      84             : 
      85             : /// isCriticalEdge - Return true if the specified edge is a critical edge.
      86             : /// Critical edges are edges from a block with multiple successors to a block
      87             : /// with multiple predecessors.
      88       10479 : bool llvm::isCriticalEdge(const Instruction *TI, unsigned SuccNum,
      89             :                           bool AllowIdenticalEdges) {
      90             :   assert(TI->isTerminator() && "Must be a terminator to have successors!");
      91             :   assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
      92       10479 :   if (TI->getNumSuccessors() == 1) return false;
      93             : 
      94        7333 :   const BasicBlock *Dest = TI->getSuccessor(SuccNum);
      95        7333 :   const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
      96             : 
      97             :   // If there is more than one predecessor, this is a critical edge...
      98             :   assert(I != E && "No preds, but we have an edge to the block?");
      99             :   const BasicBlock *FirstPred = *I;
     100             :   ++I;        // Skip one edge due to the incoming arc from TI.
     101        7333 :   if (!AllowIdenticalEdges)
     102        7160 :     return I != E;
     103             : 
     104             :   // If AllowIdenticalEdges is true, then we allow this edge to be considered
     105             :   // non-critical iff all preds come from TI's block.
     106         183 :   for (; I != E; ++I)
     107         180 :     if (*I != FirstPred)
     108             :       return true;
     109             :   return false;
     110             : }
     111             : 
     112             : // LoopInfo contains a mapping from basic block to the innermost loop. Find
     113             : // the outermost loop in the loop nest that contains BB.
     114      697361 : static const Loop *getOutermostLoop(const LoopInfo *LI, const BasicBlock *BB) {
     115             :   const Loop *L = LI->getLoopFor(BB);
     116       62614 :   if (L) {
     117       81834 :     while (const Loop *Parent = L->getParentLoop())
     118             :       L = Parent;
     119             :   }
     120      697361 :   return L;
     121             : }
     122             : 
     123             : // True if there is a loop which contains both BB1 and BB2.
     124      237893 : static bool loopContainsBoth(const LoopInfo *LI,
     125             :                              const BasicBlock *BB1, const BasicBlock *BB2) {
     126      237893 :   const Loop *L1 = getOutermostLoop(LI, BB1);
     127      237893 :   const Loop *L2 = getOutermostLoop(LI, BB2);
     128      237893 :   return L1 != nullptr && L1 == L2;
     129             : }
     130             : 
     131      237197 : bool llvm::isPotentiallyReachableFromMany(
     132             :     SmallVectorImpl<BasicBlock *> &Worklist, BasicBlock *StopBB,
     133             :     const DominatorTree *DT, const LoopInfo *LI) {
     134             :   // When the stop block is unreachable, it's dominated from everywhere,
     135             :   // regardless of whether there's a path between the two blocks.
     136      237197 :   if (DT && !DT->isReachableFromEntry(StopBB))
     137             :     DT = nullptr;
     138             : 
     139             :   // Limit the number of blocks we visit. The goal is to avoid run-away compile
     140             :   // times on large CFGs without hampering sensible code. Arbitrarily chosen.
     141             :   unsigned Limit = 32;
     142             :   SmallPtrSet<const BasicBlock*, 32> Visited;
     143             :   do {
     144             :     BasicBlock *BB = Worklist.pop_back_val();
     145     2542940 :     if (!Visited.insert(BB).second)
     146             :       continue;
     147     2201471 :     if (BB == StopBB)
     148             :       return true;
     149     2179665 :     if (DT && DT->dominates(BB, StopBB))
     150             :       return true;
     151     2146588 :     if (LI && loopContainsBoth(LI, BB, StopBB))
     152             :       return true;
     153             : 
     154     2132593 :     if (!--Limit) {
     155             :       // We haven't been able to prove it one way or the other. Conservatively
     156             :       // answer true -- that there is potentially a path.
     157             :       return true;
     158             :     }
     159             : 
     160     2086367 :     if (const Loop *Outer = LI ? getOutermostLoop(LI, BB) : nullptr) {
     161             :       // All blocks in a single loop are reachable from all other blocks. From
     162             :       // any of these blocks, we can skip directly to the exits of the loop,
     163             :       // ignoring any other blocks inside the loop body.
     164       15408 :       Outer->getExitBlocks(Worklist);
     165             :     } else {
     166     2070959 :       Worklist.append(succ_begin(BB), succ_end(BB));
     167             :     }
     168     2427836 :   } while (!Worklist.empty());
     169             : 
     170             :   // We have exhausted all possible paths and are certain that 'To' can not be
     171             :   // reached from 'From'.
     172             :   return false;
     173             : }
     174             : 
     175       51652 : bool llvm::isPotentiallyReachable(const BasicBlock *A, const BasicBlock *B,
     176             :                                   const DominatorTree *DT, const LoopInfo *LI) {
     177             :   assert(A->getParent() == B->getParent() &&
     178             :          "This analysis is function-local!");
     179             : 
     180             :   SmallVector<BasicBlock*, 32> Worklist;
     181       51652 :   Worklist.push_back(const_cast<BasicBlock*>(A));
     182             : 
     183       51652 :   return isPotentiallyReachableFromMany(Worklist, const_cast<BasicBlock *>(B),
     184       51652 :                                         DT, LI);
     185             : }
     186             : 
     187      222220 : bool llvm::isPotentiallyReachable(const Instruction *A, const Instruction *B,
     188             :                                   const DominatorTree *DT, const LoopInfo *LI) {
     189             :   assert(A->getParent()->getParent() == B->getParent()->getParent() &&
     190             :          "This analysis is function-local!");
     191             : 
     192             :   SmallVector<BasicBlock*, 32> Worklist;
     193             : 
     194      222220 :   if (A->getParent() == B->getParent()) {
     195             :     // The same block case is special because it's the only time we're looking
     196             :     // within a single block to see which instruction comes first. Once we
     197             :     // start looking at multiple blocks, the first instruction of the block is
     198             :     // reachable, so we only need to determine reachability between whole
     199             :     // blocks.
     200             :     BasicBlock *BB = const_cast<BasicBlock *>(A->getParent());
     201             : 
     202             :     // If the block is in a loop then we can reach any instruction in the block
     203             :     // from any other instruction in the block by going around a backedge.
     204       23439 :     if (LI && LI->getLoopFor(BB) != nullptr)
     205             :       return true;
     206             : 
     207             :     // Linear scan, start at 'A', see whether we hit 'B' or the end first.
     208      126360 :     for (BasicBlock::const_iterator I = A->getIterator(), E = BB->end(); I != E;
     209             :          ++I) {
     210      126350 :       if (&*I == B)
     211             :         return true;
     212             :     }
     213             : 
     214             :     // Can't be in a loop if it's the entry block -- the entry block may not
     215             :     // have predecessors.
     216          20 :     if (BB == &BB->getParent()->getEntryBlock())
     217             :       return false;
     218             : 
     219             :     // Otherwise, continue doing the normal per-BB CFG walk.
     220           6 :     Worklist.append(succ_begin(BB), succ_end(BB));
     221             : 
     222           6 :     if (Worklist.empty()) {
     223             :       // We've proven that there's no path!
     224             :       return false;
     225             :     }
     226             :   } else {
     227      204779 :     Worklist.push_back(const_cast<BasicBlock*>(A->getParent()));
     228             :   }
     229             : 
     230      409570 :   if (A->getParent() == &A->getParent()->getParent()->getEntryBlock())
     231             :     return true;
     232      204777 :   if (B->getParent() == &A->getParent()->getParent()->getEntryBlock())
     233             :     return false;
     234             : 
     235      165448 :   return isPotentiallyReachableFromMany(
     236      165448 :       Worklist, const_cast<BasicBlock *>(B->getParent()), DT, LI);
     237             : }

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