lib/VMCore/Dominators.cpp

   1 //===- Dominators.cpp - Dominator Calculation -----------------------------===//
   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 file implements simple dominator construction algorithms for finding
  11 // forward dominators.  Postdominators are available in libanalysis, but are not
  12 // included in libvmcore, because it's not needed.  Forward dominators are
  13 // needed to support the Verifier pass.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "llvm/Analysis/Dominators.h"
  18 #include "llvm/Support/CFG.h"
  19 #include "llvm/Support/Compiler.h"
  20 #include "llvm/Support/Debug.h"
  21 #include "llvm/ADT/DepthFirstIterator.h"
  22 #include "llvm/ADT/SmallPtrSet.h"
  23 #include "llvm/ADT/SmallVector.h"
  24 #include "llvm/Analysis/DominatorInternals.h"
  25 #include "llvm/Assembly/Writer.h"
  26 #include "llvm/Instructions.h"
  27 #include "llvm/Support/raw_ostream.h"
  28 #include "llvm/Support/CommandLine.h"
  29 #include <algorithm>
  30 using namespace llvm;
  31
  32 // Always verify dominfo if expensive checking is enabled.
  33 #ifdef XDEBUG
  34 static bool VerifyDomInfo = true;
  35 #else
  36 static bool VerifyDomInfo = false;
  37 #endif
  38 static cl::opt<bool,true>
  39 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
  40                cl::desc("Verify dominator info (time consuming)"));
  41
  42 //===----------------------------------------------------------------------===//
  43 //  DominatorTree Implementation
  44 //===----------------------------------------------------------------------===//
  45 //
  46 // Provide public access to DominatorTree information.  Implementation details
  47 // can be found in DominatorInternals.h.
  48 //
  49 //===----------------------------------------------------------------------===//
  50
  51 TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>);
  52 TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>);
  53
  54 char DominatorTree::ID = 0;
  55 INITIALIZE_PASS(DominatorTree, "domtree",
  56                 "Dominator Tree Construction", true, true)
  57
  58 bool DominatorTree::runOnFunction(Function &F) {
  59   DT->recalculate(F);
  60   return false;
  61 }
  62
  63 void DominatorTree::verifyAnalysis() const {
  64   if (!VerifyDomInfo) return;
  65
  66   Function &F = *getRoot()->getParent();
  67
  68   DominatorTree OtherDT;
  69   OtherDT.getBase().recalculate(F);
  70   if (compare(OtherDT)) {
  71     errs() << "DominatorTree is not up to date!\nComputed:\n";
  72     print(errs());
  73     errs() << "\nActual:\n";
  74     OtherDT.print(errs());
  75     abort();
  76   }
  77 }
  78
  79 void DominatorTree::print(raw_ostream &OS, const Module *) const {
  80   DT->print(OS);
  81 }
  82
  83 // dominates - Return true if A dominates a use in B. This performs the
  84 // special checks necessary if A and B are in the same basic block.
  85 bool DominatorTree::dominates(const Instruction *A, const Instruction *B) const{
  86   const BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
  87
  88   // If A is an invoke instruction, its value is only available in this normal
  89   // successor block.
  90   if (const InvokeInst *II = dyn_cast<InvokeInst>(A))
  91     BBA = II->getNormalDest();
  92
  93   if (BBA != BBB) return dominates(BBA, BBB);
  94
  95   // It is not possible to determine dominance between two PHI nodes
  96   // based on their ordering.
  97   if (isa<PHINode>(A) && isa<PHINode>(B))
  98     return false;
  99
 100   // Loop through the basic block until we find A or B.
 101   BasicBlock::const_iterator I = BBA->begin();
 102   for (; &*I != A && &*I != B; ++I)
 103     /*empty*/;
 104
 105   return &*I == A;
 106 }