1 files changed, 334 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/LCSSA.cpp b/contrib/llvm/lib/Transforms/Utils/LCSSA.cpp
new file mode 100644
index 0000000..b4b2e14
--- /dev/null
+++ b/contrib/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -0,0 +1,334 @@
+//===-- LCSSA.cpp - Convert loops into loop-closed SSA form ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass transforms loops by placing phi nodes at the end of the loops for
+// all values that are live across the loop boundary.  For example, it turns
+// the left into the right code:
+// 
+// for (...)                for (...)
+//   if (c)                   if (c)
+//     X1 = ...                 X1 = ...
+//   else                     else
+//     X2 = ...                 X2 = ...
+//   X3 = phi(X1, X2)         X3 = phi(X1, X2)
+// ... = X3 + 4             X4 = phi(X3)
+//                          ... = X4 + 4
+//
+// This is still valid LLVM; the extra phi nodes are purely redundant, and will
+// be trivially eliminated by InstCombine.  The major benefit of this 
+// transformation is that it makes many other loop optimizations, such as 
+// LoopUnswitching, simpler.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/PredIteratorCache.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "lcssa"
+
+STATISTIC(NumLCSSA, "Number of live out of a loop variables");
+
+/// Return true if the specified block is in the list.
+static bool isExitBlock(BasicBlock *BB,
+                        const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
+  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+    if (ExitBlocks[i] == BB)
+      return true;
+  return false;
+}
+
+/// Given an instruction in the loop, check to see if it has any uses that are
+/// outside the current loop.  If so, insert LCSSA PHI nodes and rewrite the
+/// uses.
+static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
+                               const SmallVectorImpl<BasicBlock *> &ExitBlocks,
+                               PredIteratorCache &PredCache, LoopInfo *LI) {
+  SmallVector<Use *, 16> UsesToRewrite;
+
+  // Tokens cannot be used in PHI nodes, so we skip over them.
+  // We can run into tokens which are live out of a loop with catchswitch
+  // instructions in Windows EH if the catchswitch has one catchpad which
+  // is inside the loop and another which is not.
+  if (Inst.getType()->isTokenTy())
+    return false;
+
+  BasicBlock *InstBB = Inst.getParent();
+
+  for (Use &U : Inst.uses()) {
+    Instruction *User = cast<Instruction>(U.getUser());
+    BasicBlock *UserBB = User->getParent();
+    if (PHINode *PN = dyn_cast<PHINode>(User))
+      UserBB = PN->getIncomingBlock(U);
+
+    if (InstBB != UserBB && !L.contains(UserBB))
+      UsesToRewrite.push_back(&U);
+  }
+
+  // If there are no uses outside the loop, exit with no change.
+  if (UsesToRewrite.empty())
+    return false;
+
+  ++NumLCSSA; // We are applying the transformation
+
+  // Invoke instructions are special in that their result value is not available
+  // along their unwind edge. The code below tests to see whether DomBB
+  // dominates the value, so adjust DomBB to the normal destination block,
+  // which is effectively where the value is first usable.
+  BasicBlock *DomBB = Inst.getParent();
+  if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
+    DomBB = Inv->getNormalDest();
+
+  DomTreeNode *DomNode = DT.getNode(DomBB);
+
+  SmallVector<PHINode *, 16> AddedPHIs;
+  SmallVector<PHINode *, 8> PostProcessPHIs;
+
+  SSAUpdater SSAUpdate;
+  SSAUpdate.Initialize(Inst.getType(), Inst.getName());
+
+  // Insert the LCSSA phi's into all of the exit blocks dominated by the
+  // value, and add them to the Phi's map.
+  for (BasicBlock *ExitBB : ExitBlocks) {
+    if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
+      continue;
+
+    // If we already inserted something for this BB, don't reprocess it.
+    if (SSAUpdate.HasValueForBlock(ExitBB))
+      continue;
+
+    PHINode *PN = PHINode::Create(Inst.getType(), PredCache.size(ExitBB),
+                                  Inst.getName() + ".lcssa", &ExitBB->front());
+
+    // Add inputs from inside the loop for this PHI.
+    for (BasicBlock *Pred : PredCache.get(ExitBB)) {
+      PN->addIncoming(&Inst, Pred);
+
+      // If the exit block has a predecessor not within the loop, arrange for
+      // the incoming value use corresponding to that predecessor to be
+      // rewritten in terms of a different LCSSA PHI.
+      if (!L.contains(Pred))
+        UsesToRewrite.push_back(
+            &PN->getOperandUse(PN->getOperandNumForIncomingValue(
+                 PN->getNumIncomingValues() - 1)));
+    }
+
+    AddedPHIs.push_back(PN);
+
+    // Remember that this phi makes the value alive in this block.
+    SSAUpdate.AddAvailableValue(ExitBB, PN);
+
+    // LoopSimplify might fail to simplify some loops (e.g. when indirect
+    // branches are involved). In such situations, it might happen that an exit
+    // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
+    // PHIs in such an exit block, we are also inserting PHIs into L2's header.
+    // This could break LCSSA form for L2 because these inserted PHIs can also
+    // have uses outside of L2. Remember all PHIs in such situation as to
+    // revisit than later on. FIXME: Remove this if indirectbr support into
+    // LoopSimplify gets improved.
+    if (auto *OtherLoop = LI->getLoopFor(ExitBB))
+      if (!L.contains(OtherLoop))
+        PostProcessPHIs.push_back(PN);
+  }
+
+  // Rewrite all uses outside the loop in terms of the new PHIs we just
+  // inserted.
+  for (Use *UseToRewrite : UsesToRewrite) {
+    // If this use is in an exit block, rewrite to use the newly inserted PHI.
+    // This is required for correctness because SSAUpdate doesn't handle uses in
+    // the same block.  It assumes the PHI we inserted is at the end of the
+    // block.
+    Instruction *User = cast<Instruction>(UseToRewrite->getUser());
+    BasicBlock *UserBB = User->getParent();
+    if (PHINode *PN = dyn_cast<PHINode>(User))
+      UserBB = PN->getIncomingBlock(*UseToRewrite);
+
+    if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) {
+      // Tell the VHs that the uses changed. This updates SCEV's caches.
+      if (UseToRewrite->get()->hasValueHandle())
+        ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front());
+      UseToRewrite->set(&UserBB->front());
+      continue;
+    }
+
+    // Otherwise, do full PHI insertion.
+    SSAUpdate.RewriteUse(*UseToRewrite);
+  }
+
+  // Post process PHI instructions that were inserted into another disjoint loop
+  // and update their exits properly.
+  for (auto *I : PostProcessPHIs) {
+    if (I->use_empty())
+      continue;
+
+    BasicBlock *PHIBB = I->getParent();
+    Loop *OtherLoop = LI->getLoopFor(PHIBB);
+    SmallVector<BasicBlock *, 8> EBs;
+    OtherLoop->getExitBlocks(EBs);
+    if (EBs.empty())
+      continue;
+
+    // Recurse and re-process each PHI instruction. FIXME: we should really
+    // convert this entire thing to a worklist approach where we process a
+    // vector of instructions...
+    processInstruction(*OtherLoop, *I, DT, EBs, PredCache, LI);
+  }
+
+  // Remove PHI nodes that did not have any uses rewritten.
+  for (PHINode *PN : AddedPHIs)
+    if (PN->use_empty())
+      PN->eraseFromParent();
+
+  return true;
+}
+
+/// Return true if the specified block dominates at least
+/// one of the blocks in the specified list.
+static bool
+blockDominatesAnExit(BasicBlock *BB,
+                     DominatorTree &DT,
+                     const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
+  DomTreeNode *DomNode = DT.getNode(BB);
+  for (BasicBlock *ExitBB : ExitBlocks)
+    if (DT.dominates(DomNode, DT.getNode(ExitBB)))
+      return true;
+
+  return false;
+}
+
+bool llvm::formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
+                     ScalarEvolution *SE) {
+  bool Changed = false;
+
+  // Get the set of exiting blocks.
+  SmallVector<BasicBlock *, 8> ExitBlocks;
+  L.getExitBlocks(ExitBlocks);
+
+  if (ExitBlocks.empty())
+    return false;
+
+  PredIteratorCache PredCache;
+
+  // Look at all the instructions in the loop, checking to see if they have uses
+  // outside the loop.  If so, rewrite those uses.
+  for (BasicBlock *BB : L.blocks()) {
+    // For large loops, avoid use-scanning by using dominance information:  In
+    // particular, if a block does not dominate any of the loop exits, then none
+    // of the values defined in the block could be used outside the loop.
+    if (!blockDominatesAnExit(BB, DT, ExitBlocks))
+      continue;
+
+    for (Instruction &I : *BB) {
+      // Reject two common cases fast: instructions with no uses (like stores)
+      // and instructions with one use that is in the same block as this.
+      if (I.use_empty() ||
+          (I.hasOneUse() && I.user_back()->getParent() == BB &&
+           !isa<PHINode>(I.user_back())))
+        continue;
+
+      Changed |= processInstruction(L, I, DT, ExitBlocks, PredCache, LI);
+    }
+  }
+
+  // If we modified the code, remove any caches about the loop from SCEV to
+  // avoid dangling entries.
+  // FIXME: This is a big hammer, can we clear the cache more selectively?
+  if (SE && Changed)
+    SE->forgetLoop(&L);
+
+  assert(L.isLCSSAForm(DT));
+
+  return Changed;
+}
+
+/// Process a loop nest depth first.
+bool llvm::formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
+                                ScalarEvolution *SE) {
+  bool Changed = false;
+
+  // Recurse depth-first through inner loops.
+  for (Loop *SubLoop : L.getSubLoops())
+    Changed |= formLCSSARecursively(*SubLoop, DT, LI, SE);
+
+  Changed |= formLCSSA(L, DT, LI, SE);
+  return Changed;
+}
+
+namespace {
+struct LCSSA : public FunctionPass {
+  static char ID; // Pass identification, replacement for typeid
+  LCSSA() : FunctionPass(ID) {
+    initializeLCSSAPass(*PassRegistry::getPassRegistry());
+  }
+
+  // Cached analysis information for the current function.
+  DominatorTree *DT;
+  LoopInfo *LI;
+  ScalarEvolution *SE;
+
+  bool runOnFunction(Function &F) override;
+
+  /// This transformation requires natural loop information & requires that
+  /// loop preheaders be inserted into the CFG.  It maintains both of these,
+  /// as well as the CFG.  It also requires dominator information.
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+
+    AU.addRequired<DominatorTreeWrapperPass>();
+    AU.addRequired<LoopInfoWrapperPass>();
+    AU.addPreservedID(LoopSimplifyID);
+    AU.addPreserved<AAResultsWrapperPass>();
+    AU.addPreserved<GlobalsAAWrapperPass>();
+    AU.addPreserved<ScalarEvolutionWrapperPass>();
+    AU.addPreserved<SCEVAAWrapperPass>();
+  }
+};
+}
+
+char LCSSA::ID = 0;
+INITIALIZE_PASS_BEGIN(LCSSA, "lcssa", "Loop-Closed SSA Form Pass", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass)
+INITIALIZE_PASS_END(LCSSA, "lcssa", "Loop-Closed SSA Form Pass", false, false)
+
+Pass *llvm::createLCSSAPass() { return new LCSSA(); }
+char &llvm::LCSSAID = LCSSA::ID;
+
+
+/// Process all loops in the function, inner-most out.
+bool LCSSA::runOnFunction(Function &F) {
+  bool Changed = false;
+  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
+  SE = SEWP ? &SEWP->getSE() : nullptr;
+
+  // Simplify each loop nest in the function.
+  for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
+    Changed |= formLCSSARecursively(**I, *DT, LI, SE);
+
+  return Changed;
+}
+