Imported Upstream version 5.18.0.179

Former-commit-id: 67aa10e65b237e1c4537630979ee99ebe1374215

external/llvm/lib/Analysis/CFG.cpp

@@ -0,0 +1,236 @@
+//===-- CFG.cpp - BasicBlock analysis --------------------------------------==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This family of functions performs analyses on basic blocks, and instructions
+// contained within basic blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/CFG.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/Dominators.h"
+
+using namespace llvm;
+
+/// FindFunctionBackedges - Analyze the specified function to find all of the
+/// loop backedges in the function and return them.  This is a relatively cheap
+/// (compared to computing dominators and loop info) analysis.
+///
+/// The output is added to Result, as pairs of <from,to> edge info.
+void llvm::FindFunctionBackedges(const Function &F,
+     SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
+  const BasicBlock *BB = &F.getEntryBlock();
+  if (succ_empty(BB))
+    return;
+
+  SmallPtrSet<const BasicBlock*, 8> Visited;
+  SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
+  SmallPtrSet<const BasicBlock*, 8> InStack;
+
+  Visited.insert(BB);
+  VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
+  InStack.insert(BB);
+  do {
+    std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
+    const BasicBlock *ParentBB = Top.first;
+    succ_const_iterator &I = Top.second;
+
+    bool FoundNew = false;
+    while (I != succ_end(ParentBB)) {
+      BB = *I++;
+      if (Visited.insert(BB).second) {
+        FoundNew = true;
+        break;
+      }
+      // Successor is in VisitStack, it's a back edge.
+      if (InStack.count(BB))
+        Result.push_back(std::make_pair(ParentBB, BB));
+    }
+
+    if (FoundNew) {
+      // Go down one level if there is a unvisited successor.
+      InStack.insert(BB);
+      VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
+    } else {
+      // Go up one level.
+      InStack.erase(VisitStack.pop_back_val().first);
+    }
+  } while (!VisitStack.empty());
+}
+
+/// GetSuccessorNumber - Search for the specified successor of basic block BB
+/// and return its position in the terminator instruction's list of
+/// successors.  It is an error to call this with a block that is not a
+/// successor.
+unsigned llvm::GetSuccessorNumber(const BasicBlock *BB,
+    const BasicBlock *Succ) {
+  const TerminatorInst *Term = BB->getTerminator();
+#ifndef NDEBUG
+  unsigned e = Term->getNumSuccessors();
+#endif
+  for (unsigned i = 0; ; ++i) {
+    assert(i != e && "Didn't find edge?");
+    if (Term->getSuccessor(i) == Succ)
+      return i;
+  }
+}
+
+/// isCriticalEdge - Return true if the specified edge is a critical edge.
+/// Critical edges are edges from a block with multiple successors to a block
+/// with multiple predecessors.
+bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
+                          bool AllowIdenticalEdges) {
+  assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
+  if (TI->getNumSuccessors() == 1) return false;
+
+  const BasicBlock *Dest = TI->getSuccessor(SuccNum);
+  const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
+
+  // If there is more than one predecessor, this is a critical edge...
+  assert(I != E && "No preds, but we have an edge to the block?");
+  const BasicBlock *FirstPred = *I;
+  ++I;        // Skip one edge due to the incoming arc from TI.
+  if (!AllowIdenticalEdges)
+    return I != E;
+
+  // If AllowIdenticalEdges is true, then we allow this edge to be considered
+  // non-critical iff all preds come from TI's block.
+  for (; I != E; ++I)
+    if (*I != FirstPred)
+      return true;
+  return false;
+}
+
+// LoopInfo contains a mapping from basic block to the innermost loop. Find
+// the outermost loop in the loop nest that contains BB.
+static const Loop *getOutermostLoop(const LoopInfo *LI, const BasicBlock *BB) {
+  const Loop *L = LI->getLoopFor(BB);
+  if (L) {
+    while (const Loop *Parent = L->getParentLoop())
+      L = Parent;
+  }
+  return L;
+}
+
+// True if there is a loop which contains both BB1 and BB2.
+static bool loopContainsBoth(const LoopInfo *LI,
+                             const BasicBlock *BB1, const BasicBlock *BB2) {
+  const Loop *L1 = getOutermostLoop(LI, BB1);
+  const Loop *L2 = getOutermostLoop(LI, BB2);
+  return L1 != nullptr && L1 == L2;
+}
+
+bool llvm::isPotentiallyReachableFromMany(
+    SmallVectorImpl<BasicBlock *> &Worklist, BasicBlock *StopBB,
+    const DominatorTree *DT, const LoopInfo *LI) {
+  // When the stop block is unreachable, it's dominated from everywhere,
+  // regardless of whether there's a path between the two blocks.
+  if (DT && !DT->isReachableFromEntry(StopBB))
+    DT = nullptr;
+
+  // Limit the number of blocks we visit. The goal is to avoid run-away compile
+  // times on large CFGs without hampering sensible code. Arbitrarily chosen.
+  unsigned Limit = 32;
+  SmallPtrSet<const BasicBlock*, 32> Visited;
+  do {
+    BasicBlock *BB = Worklist.pop_back_val();
+    if (!Visited.insert(BB).second)
+      continue;
+    if (BB == StopBB)
+      return true;
+    if (DT && DT->dominates(BB, StopBB))
+      return true;
+    if (LI && loopContainsBoth(LI, BB, StopBB))
+      return true;
+
+    if (!--Limit) {
+      // We haven't been able to prove it one way or the other. Conservatively
+      // answer true -- that there is potentially a path.
+      return true;
+    }
+
+    if (const Loop *Outer = LI ? getOutermostLoop(LI, BB) : nullptr) {
+      // All blocks in a single loop are reachable from all other blocks. From
+      // any of these blocks, we can skip directly to the exits of the loop,
+      // ignoring any other blocks inside the loop body.
+      Outer->getExitBlocks(Worklist);
+    } else {
+      Worklist.append(succ_begin(BB), succ_end(BB));
+    }
+  } while (!Worklist.empty());
+
+  // We have exhausted all possible paths and are certain that 'To' can not be
+  // reached from 'From'.
+  return false;
+}
+
+bool llvm::isPotentiallyReachable(const BasicBlock *A, const BasicBlock *B,
+                                  const DominatorTree *DT, const LoopInfo *LI) {
+  assert(A->getParent() == B->getParent() &&
+         "This analysis is function-local!");
+
+  SmallVector<BasicBlock*, 32> Worklist;
+  Worklist.push_back(const_cast<BasicBlock*>(A));
+
+  return isPotentiallyReachableFromMany(Worklist, const_cast<BasicBlock *>(B),
+                                        DT, LI);
+}
+
+bool llvm::isPotentiallyReachable(const Instruction *A, const Instruction *B,
+                                  const DominatorTree *DT, const LoopInfo *LI) {
+  assert(A->getParent()->getParent() == B->getParent()->getParent() &&
+         "This analysis is function-local!");
+
+  SmallVector<BasicBlock*, 32> Worklist;
+
+  if (A->getParent() == B->getParent()) {
+    // The same block case is special because it's the only time we're looking
+    // within a single block to see which instruction comes first. Once we
+    // start looking at multiple blocks, the first instruction of the block is
+    // reachable, so we only need to determine reachability between whole
+    // blocks.
+    BasicBlock *BB = const_cast<BasicBlock *>(A->getParent());
+
+    // If the block is in a loop then we can reach any instruction in the block
+    // from any other instruction in the block by going around a backedge.
+    if (LI && LI->getLoopFor(BB) != nullptr)
+      return true;
+
+    // Linear scan, start at 'A', see whether we hit 'B' or the end first.
+    for (BasicBlock::const_iterator I = A->getIterator(), E = BB->end(); I != E;
+         ++I) {
+      if (&*I == B)
+        return true;
+    }
+
+    // Can't be in a loop if it's the entry block -- the entry block may not
+    // have predecessors.
+    if (BB == &BB->getParent()->getEntryBlock())
+      return false;
+
+    // Otherwise, continue doing the normal per-BB CFG walk.
+    Worklist.append(succ_begin(BB), succ_end(BB));
+
+    if (Worklist.empty()) {
+      // We've proven that there's no path!
+      return false;
+    }
+  } else {
+    Worklist.push_back(const_cast<BasicBlock*>(A->getParent()));
+  }
+
+  if (A->getParent() == &A->getParent()->getParent()->getEntryBlock())
+    return true;
+  if (B->getParent() == &A->getParent()->getParent()->getEntryBlock())
+    return false;
+
+  return isPotentiallyReachableFromMany(
+      Worklist, const_cast<BasicBlock *>(B->getParent()), DT, LI);
+}