Update llvm to r84119.

1 files changed, 232 insertions, 47 deletions

diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp
index f605783..32d2266 100644
--- a/lib/Analysis/LoopDependenceAnalysis.cpp
+++ b/lib/Analysis/LoopDependenceAnalysis.cpp
@@ -15,18 +15,33 @@
 //
 // TODO: adapt as implementation progresses.
 //
+// TODO: document lingo (pair, subscript, index)
+//
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "lda"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/LoopDependenceAnalysis.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Instructions.h"
+#include "llvm/Operator.h"
+#include "llvm/Support/Allocator.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetData.h"
 using namespace llvm;
 
+STATISTIC(NumAnswered,    "Number of dependence queries answered");
+STATISTIC(NumAnalysed,    "Number of distinct dependence pairs analysed");
+STATISTIC(NumDependent,   "Number of pairs with dependent accesses");
+STATISTIC(NumIndependent, "Number of pairs with independent accesses");
+STATISTIC(NumUnknown,     "Number of pairs with unknown accesses");
+
 LoopPass *llvm::createLoopDependenceAnalysisPass() {
   return new LoopDependenceAnalysis();
 }
@@ -44,14 +59,14 @@ static inline bool IsMemRefInstr(const Value *V) {
   return I && (I->mayReadFromMemory() || I->mayWriteToMemory());
 }
 
-static void GetMemRefInstrs(
-    const Loop *L, SmallVectorImpl<Instruction*> &memrefs) {
+static void GetMemRefInstrs(const Loop *L,
+                            SmallVectorImpl<Instruction*> &Memrefs) {
   for (Loop::block_iterator b = L->block_begin(), be = L->block_end();
-      b != be; ++b)
+       b != be; ++b)
     for (BasicBlock::iterator i = (*b)->begin(), ie = (*b)->end();
-        i != ie; ++i)
+         i != ie; ++i)
       if (IsMemRefInstr(i))
-        memrefs.push_back(i);
+        Memrefs.push_back(i);
 }
 
 static bool IsLoadOrStoreInst(Value *I) {
@@ -63,53 +78,223 @@ static Value *GetPointerOperand(Value *I) {
     return i->getPointerOperand();
   if (StoreInst *i = dyn_cast<StoreInst>(I))
     return i->getPointerOperand();
-  assert(0 && "Value is no load or store instruction!");
+  llvm_unreachable("Value is no load or store instruction!");
   // Never reached.
   return 0;
 }
 
+static AliasAnalysis::AliasResult UnderlyingObjectsAlias(AliasAnalysis *AA,
+                                                         const Value *A,
+                                                         const Value *B) {
+  const Value *aObj = A->getUnderlyingObject();
+  const Value *bObj = B->getUnderlyingObject();
+  return AA->alias(aObj, AA->getTypeStoreSize(aObj->getType()),
+                   bObj, AA->getTypeStoreSize(bObj->getType()));
+}
+
+static inline const SCEV *GetZeroSCEV(ScalarEvolution *SE) {
+  return SE->getConstant(Type::getInt32Ty(SE->getContext()), 0L);
+}
+
 //===----------------------------------------------------------------------===//
 //                             Dependence Testing
 //===----------------------------------------------------------------------===//
 
-bool LoopDependenceAnalysis::isDependencePair(const Value *x,
-                                              const Value *y) const {
-  return IsMemRefInstr(x) &&
-         IsMemRefInstr(y) &&
-         (cast<const Instruction>(x)->mayWriteToMemory() ||
-          cast<const Instruction>(y)->mayWriteToMemory());
+bool LoopDependenceAnalysis::isDependencePair(const Value *A,
+                                              const Value *B) const {
+  return IsMemRefInstr(A) &&
+         IsMemRefInstr(B) &&
+         (cast<const Instruction>(A)->mayWriteToMemory() ||
+          cast<const Instruction>(B)->mayWriteToMemory());
+}
+
+bool LoopDependenceAnalysis::findOrInsertDependencePair(Value *A,
+                                                        Value *B,
+                                                        DependencePair *&P) {
+  void *insertPos = 0;
+  FoldingSetNodeID id;
+  id.AddPointer(A);
+  id.AddPointer(B);
+
+  P = Pairs.FindNodeOrInsertPos(id, insertPos);
+  if (P) return true;
+
+  P = PairAllocator.Allocate<DependencePair>();
+  new (P) DependencePair(id, A, B);
+  Pairs.InsertNode(P, insertPos);
+  return false;
+}
+
+void LoopDependenceAnalysis::getLoops(const SCEV *S,
+                                      DenseSet<const Loop*>* Loops) const {
+  // Refactor this into an SCEVVisitor, if efficiency becomes a concern.
+  for (const Loop *L = this->L; L != 0; L = L->getParentLoop())
+    if (!S->isLoopInvariant(L))
+      Loops->insert(L);
+}
+
+bool LoopDependenceAnalysis::isLoopInvariant(const SCEV *S) const {
+  DenseSet<const Loop*> loops;
+  getLoops(S, &loops);
+  return loops.empty();
+}
+
+bool LoopDependenceAnalysis::isAffine(const SCEV *S) const {
+  const SCEVAddRecExpr *rec = dyn_cast<SCEVAddRecExpr>(S);
+  return isLoopInvariant(S) || (rec && rec->isAffine());
+}
+
+bool LoopDependenceAnalysis::isZIVPair(const SCEV *A, const SCEV *B) const {
+  return isLoopInvariant(A) && isLoopInvariant(B);
+}
+
+bool LoopDependenceAnalysis::isSIVPair(const SCEV *A, const SCEV *B) const {
+  DenseSet<const Loop*> loops;
+  getLoops(A, &loops);
+  getLoops(B, &loops);
+  return loops.size() == 1;
+}
+
+LoopDependenceAnalysis::DependenceResult
+LoopDependenceAnalysis::analyseZIV(const SCEV *A,
+                                   const SCEV *B,
+                                   Subscript *S) const {
+  assert(isZIVPair(A, B) && "Attempted to ZIV-test non-ZIV SCEVs!");
+  return A == B ? Dependent : Independent;
 }
 
-bool LoopDependenceAnalysis::depends(Value *src, Value *dst) {
-  assert(isDependencePair(src, dst) && "Values form no dependence pair!");
-  DOUT << "== LDA test ==\n" << *src << *dst;
+LoopDependenceAnalysis::DependenceResult
+LoopDependenceAnalysis::analyseSIV(const SCEV *A,
+                                   const SCEV *B,
+                                   Subscript *S) const {
+  return Unknown; // TODO: Implement.
+}
+
+LoopDependenceAnalysis::DependenceResult
+LoopDependenceAnalysis::analyseMIV(const SCEV *A,
+                                   const SCEV *B,
+                                   Subscript *S) const {
+  return Unknown; // TODO: Implement.
+}
 
-  // We only analyse loads and stores; for possible memory accesses by e.g.
-  // free, call, or invoke instructions we conservatively assume dependence.
-  if (!IsLoadOrStoreInst(src) || !IsLoadOrStoreInst(dst))
-    return true;
+LoopDependenceAnalysis::DependenceResult
+LoopDependenceAnalysis::analyseSubscript(const SCEV *A,
+                                         const SCEV *B,
+                                         Subscript *S) const {
+  DEBUG(errs() << "  Testing subscript: " << *A << ", " << *B << "\n");
 
-  Value *srcPtr = GetPointerOperand(src);
-  Value *dstPtr = GetPointerOperand(dst);
-  const Value *srcObj = srcPtr->getUnderlyingObject();
-  const Value *dstObj = dstPtr->getUnderlyingObject();
-  AliasAnalysis::AliasResult alias = AA->alias(
-      srcObj, AA->getTargetData().getTypeStoreSize(srcObj->getType()),
-      dstObj, AA->getTargetData().getTypeStoreSize(dstObj->getType()));
+  if (A == B) {
+    DEBUG(errs() << "  -> [D] same SCEV\n");
+    return Dependent;
+  }
 
-  // If we don't know whether or not the two objects alias, assume dependence.
-  if (alias == AliasAnalysis::MayAlias)
-    return true;
+  if (!isAffine(A) || !isAffine(B)) {
+    DEBUG(errs() << "  -> [?] not affine\n");
+    return Unknown;
+  }
 
-  // If the objects noalias, they are distinct, accesses are independent.
-  if (alias == AliasAnalysis::NoAlias)
-    return false;
+  if (isZIVPair(A, B))
+    return analyseZIV(A, B, S);
 
-  // TODO: the underlying objects MustAlias, test for dependence
+  if (isSIVPair(A, B))
+    return analyseSIV(A, B, S);
 
-  // We couldn't establish a more precise result, so we have to conservatively
-  // assume full dependence.
-  return true;
+  return analyseMIV(A, B, S);
+}
+
+LoopDependenceAnalysis::DependenceResult
+LoopDependenceAnalysis::analysePair(DependencePair *P) const {
+  DEBUG(errs() << "Analysing:\n" << *P->A << "\n" << *P->B << "\n");
+
+  // We only analyse loads and stores but no possible memory accesses by e.g.
+  // free, call, or invoke instructions.
+  if (!IsLoadOrStoreInst(P->A) || !IsLoadOrStoreInst(P->B)) {
+    DEBUG(errs() << "--> [?] no load/store\n");
+    return Unknown;
+  }
+
+  Value *aPtr = GetPointerOperand(P->A);
+  Value *bPtr = GetPointerOperand(P->B);
+
+  switch (UnderlyingObjectsAlias(AA, aPtr, bPtr)) {
+  case AliasAnalysis::MayAlias:
+    // We can not analyse objects if we do not know about their aliasing.
+    DEBUG(errs() << "---> [?] may alias\n");
+    return Unknown;
+
+  case AliasAnalysis::NoAlias:
+    // If the objects noalias, they are distinct, accesses are independent.
+    DEBUG(errs() << "---> [I] no alias\n");
+    return Independent;
+
+  case AliasAnalysis::MustAlias:
+    break; // The underlying objects alias, test accesses for dependence.
+  }
+
+  const GEPOperator *aGEP = dyn_cast<GEPOperator>(aPtr);
+  const GEPOperator *bGEP = dyn_cast<GEPOperator>(bPtr);
+
+  if (!aGEP || !bGEP)
+    return Unknown;
+
+  // FIXME: Is filtering coupled subscripts necessary?
+
+  // Collect GEP operand pairs (FIXME: use GetGEPOperands from BasicAA), adding
+  // trailing zeroes to the smaller GEP, if needed.
+  typedef SmallVector<std::pair<const SCEV*, const SCEV*>, 4> GEPOpdPairsTy;
+  GEPOpdPairsTy opds;
+  for(GEPOperator::const_op_iterator aIdx = aGEP->idx_begin(),
+                                     aEnd = aGEP->idx_end(),
+                                     bIdx = bGEP->idx_begin(),
+                                     bEnd = bGEP->idx_end();
+      aIdx != aEnd && bIdx != bEnd;
+      aIdx += (aIdx != aEnd), bIdx += (bIdx != bEnd)) {
+    const SCEV* aSCEV = (aIdx != aEnd) ? SE->getSCEV(*aIdx) : GetZeroSCEV(SE);
+    const SCEV* bSCEV = (bIdx != bEnd) ? SE->getSCEV(*bIdx) : GetZeroSCEV(SE);
+    opds.push_back(std::make_pair(aSCEV, bSCEV));
+  }
+
+  if (!opds.empty() && opds[0].first != opds[0].second) {
+    // We cannot (yet) handle arbitrary GEP pointer offsets. By limiting
+    //
+    // TODO: this could be relaxed by adding the size of the underlying object
+    // to the first subscript. If we have e.g. (GEP x,0,i; GEP x,2,-i) and we
+    // know that x is a [100 x i8]*, we could modify the first subscript to be
+    // (i, 200-i) instead of (i, -i).
+    return Unknown;
+  }
+
+  // Now analyse the collected operand pairs (skipping the GEP ptr offsets).
+  for (GEPOpdPairsTy::const_iterator i = opds.begin() + 1, end = opds.end();
+       i != end; ++i) {
+    Subscript subscript;
+    DependenceResult result = analyseSubscript(i->first, i->second, &subscript);
+    if (result != Dependent) {
+      // We either proved independence or failed to analyse this subscript.
+      // Further subscripts will not improve the situation, so abort early.
+      return result;
+    }
+    P->Subscripts.push_back(subscript);
+  }
+  // We successfully analysed all subscripts but failed to prove independence.
+  return Dependent;
+}
+
+bool LoopDependenceAnalysis::depends(Value *A, Value *B) {
+  assert(isDependencePair(A, B) && "Values form no dependence pair!");
+  ++NumAnswered;
+
+  DependencePair *p;
+  if (!findOrInsertDependencePair(A, B, p)) {
+    // The pair is not cached, so analyse it.
+    ++NumAnalysed;
+    switch (p->Result = analysePair(p)) {
+    case Dependent:   ++NumDependent;   break;
+    case Independent: ++NumIndependent; break;
+    case Unknown:     ++NumUnknown;     break;
+    }
+  }
+  return p->Result != Independent;
 }
 
 //===----------------------------------------------------------------------===//
@@ -123,14 +308,19 @@ bool LoopDependenceAnalysis::runOnLoop(Loop *L, LPPassManager &) {
   return false;
 }
 
+void LoopDependenceAnalysis::releaseMemory() {
+  Pairs.clear();
+  PairAllocator.Reset();
+}
+
 void LoopDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesAll();
   AU.addRequiredTransitive<AliasAnalysis>();
   AU.addRequiredTransitive<ScalarEvolution>();
 }
 
-static void PrintLoopInfo(
-    raw_ostream &OS, LoopDependenceAnalysis *LDA, const Loop *L) {
+static void PrintLoopInfo(raw_ostream &OS,
+                          LoopDependenceAnalysis *LDA, const Loop *L) {
   if (!L->empty()) return; // ignore non-innermost loops
 
   SmallVector<Instruction*, 8> memrefs;
@@ -142,14 +332,14 @@ static void PrintLoopInfo(
 
   OS << "  Load/store instructions: " << memrefs.size() << "\n";
   for (SmallVector<Instruction*, 8>::const_iterator x = memrefs.begin(),
-      end = memrefs.end(); x != end; ++x)
-    OS << "\t" << (x - memrefs.begin()) << ": " << **x;
+       end = memrefs.end(); x != end; ++x)
+    OS << "\t" << (x - memrefs.begin()) << ": " << **x << "\n";
 
   OS << "  Pairwise dependence results:\n";
   for (SmallVector<Instruction*, 8>::const_iterator x = memrefs.begin(),
-      end = memrefs.end(); x != end; ++x)
+       end = memrefs.end(); x != end; ++x)
     for (SmallVector<Instruction*, 8>::const_iterator y = x + 1;
-        y != end; ++y)
+         y != end; ++y)
       if (LDA->isDependencePair(*x, *y))
         OS << "\t" << (x - memrefs.begin()) << "," << (y - memrefs.begin())
            << ": " << (LDA->depends(*x, *y) ? "dependent" : "independent")
@@ -160,8 +350,3 @@ void LoopDependenceAnalysis::print(raw_ostream &OS, const Module*) const {
   // TODO: doc why const_cast is safe
   PrintLoopInfo(OS, const_cast<LoopDependenceAnalysis*>(this), this->L);
 }
-
-void LoopDependenceAnalysis::print(std::ostream &OS, const Module *M) const {
-  raw_os_ostream os(OS);
-  print(os, M);
-}