Introduce a pointertracking pass.

For now this only computes the allocated size of the memory pointed to by a
pointer, and offset a pointer from allocated pointer.
The actual checkLimits part will come later, after another round of review.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75657 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 261 insertions, 0 deletions

diff --git a/lib/Analysis/PointerTracking.cpp b/lib/Analysis/PointerTracking.cpp
new file mode 100644
index 0000000..1ae2fe6
--- /dev/null
+++ b/lib/Analysis/PointerTracking.cpp
@@ -0,0 +1,261 @@
+//===- PointerTracking.cpp - Pointer Bounds Tracking ------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements tracking of pointer bounds.
+//
+//===----------------------------------------------------------------------===//
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/PointerTracking.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Constants.h"
+#include "llvm/Module.h"
+#include "llvm/Value.h"
+#include "llvm/Support/CallSite.h"
+#include "llvm/Support/InstIterator.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetData.h"
+
+namespace llvm {
+char PointerTracking::ID=0;
+PointerTracking::PointerTracking() : FunctionPass(&ID) {}
+
+bool PointerTracking::runOnFunction(Function &F) {
+  predCache.clear();
+  assert(analyzing.empty());
+  FF = &F;
+  TD = getAnalysisIfAvailable<TargetData>();
+  SE = &getAnalysis<ScalarEvolution>();
+  LI = &getAnalysis<LoopInfo>();
+  DT = &getAnalysis<DominatorTree>();
+  return false;
+}
+
+void PointerTracking::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequiredTransitive<DominatorTree>();
+  AU.addRequiredTransitive<LoopInfo>();
+  AU.addRequiredTransitive<ScalarEvolution>();
+  AU.setPreservesAll();
+}
+
+bool PointerTracking::doInitialization(Module &M) {
+  const Type *PTy = PointerType::getUnqual(Type::Int8Ty);
+
+  // Find calloc(i64, i64) or calloc(i32, i32).
+  callocFunc = M.getFunction("calloc");
+  if (callocFunc) {
+    const FunctionType *Ty = callocFunc->getFunctionType();
+
+    std::vector<const Type*> args, args2;
+    args.push_back(Type::Int64Ty);
+    args.push_back(Type::Int64Ty);
+    args2.push_back(Type::Int32Ty);
+    args2.push_back(Type::Int32Ty);
+    const FunctionType *Calloc1Type =
+      FunctionType::get(PTy, args, false);
+    const FunctionType *Calloc2Type =
+      FunctionType::get(PTy, args2, false);
+    if (Ty != Calloc1Type && Ty != Calloc2Type)
+      callocFunc = 0; // Give up
+  }
+
+  // Find realloc(i8*, i64) or realloc(i8*, i32).
+  reallocFunc = M.getFunction("realloc");
+  if (reallocFunc) {
+    const FunctionType *Ty = reallocFunc->getFunctionType();
+    std::vector<const Type*> args, args2;
+    args.push_back(PTy);
+    args.push_back(Type::Int64Ty);
+    args2.push_back(PTy);
+    args2.push_back(Type::Int32Ty);
+
+    const FunctionType *Realloc1Type =
+      FunctionType::get(PTy, args, false);
+    const FunctionType *Realloc2Type =
+      FunctionType::get(PTy, args2, false);
+    if (Ty != Realloc1Type && Ty != Realloc2Type)
+      reallocFunc = 0; // Give up
+  }
+  return false;
+}
+
+// Calculates the number of elements allocated for pointer P,
+// the type of the element is stored in Ty.
+const SCEV *PointerTracking::computeAllocationCount(Value *P,
+                                                    const Type *&Ty) const {
+  Value *V = P->stripPointerCasts();
+  if (AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
+    Value *arraySize = AI->getArraySize();
+    Ty = AI->getAllocatedType();
+    // arraySize elements of type Ty.
+    return SE->getSCEV(arraySize);
+  }
+
+  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
+    if (GV->hasDefinitiveInitializer()) {
+      Constant *C = GV->getInitializer();
+      if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
+        Ty = ATy->getElementType();
+        return SE->getConstant(Type::Int32Ty, ATy->getNumElements());
+      }
+    }
+    Ty = GV->getType();
+    return SE->getConstant(Type::Int32Ty, 1);
+    //TODO: implement more tracking for globals
+  }
+
+  if (CallInst *CI = dyn_cast<CallInst>(V)) {
+    CallSite CS(CI);
+    Function *F = dyn_cast<Function>(CS.getCalledValue()->stripPointerCasts());
+    const Loop *L = LI->getLoopFor(CI->getParent());
+    if (F == callocFunc) {
+      Ty = Type::Int8Ty;
+      // calloc allocates arg0*arg1 bytes.
+      return SE->getSCEVAtScope(SE->getMulExpr(SE->getSCEV(CS.getArgument(0)),
+                                               SE->getSCEV(CS.getArgument(1))),
+                                L);
+    } else if (F == reallocFunc) {
+      Ty = Type::Int8Ty;
+      // realloc allocates arg1 bytes.
+      return SE->getSCEVAtScope(CS.getArgument(1), L);
+    }
+  }
+
+  return SE->getCouldNotCompute();
+}
+
+// Calculates the number of elements of type Ty allocated for P.
+const SCEV *PointerTracking::computeAllocationCountForType(Value *P,
+                                                           const Type *Ty)
+  const {
+    const Type *elementTy;
+    const SCEV *Count = computeAllocationCount(P, elementTy);
+    if (isa<SCEVCouldNotCompute>(Count))
+      return Count;
+    if (elementTy == Ty)
+      return Count;
+
+    if (!TD) // need TargetData from this point forward
+      return SE->getCouldNotCompute();
+
+    uint64_t elementSize = TD->getTypeAllocSize(elementTy);
+    uint64_t wantSize = TD->getTypeAllocSize(Ty);
+    if (elementSize == wantSize)
+      return Count;
+    if (elementSize % wantSize) //fractional counts not possible
+      return SE->getCouldNotCompute();
+    return SE->getMulExpr(Count, SE->getConstant(Count->getType(),
+                                                 elementSize/wantSize));
+}
+
+const SCEV *PointerTracking::getAllocationElementCount(Value *V) const {
+  // We only deal with pointers.
+  const PointerType *PTy = cast<PointerType>(V->getType());
+  return computeAllocationCountForType(V, PTy->getElementType());
+}
+
+const SCEV *PointerTracking::getAllocationSizeInBytes(Value *V) const {
+  return computeAllocationCountForType(V, Type::Int8Ty);
+}
+
+// Helper for isLoopGuardedBy that checks the swapped and inverted predicate too
+enum SolverResult PointerTracking::isLoopGuardedBy(const Loop *L,
+                                                   Predicate Pred,
+                                                   const SCEV *A,
+                                                   const SCEV *B) const {
+  if (SE->isLoopGuardedByCond(L, Pred, A, B))
+    return AlwaysTrue;
+  Pred = ICmpInst::getSwappedPredicate(Pred);
+  if (SE->isLoopGuardedByCond(L, Pred, B, A))
+    return AlwaysTrue;
+
+  Pred = ICmpInst::getInversePredicate(Pred);
+  if (SE->isLoopGuardedByCond(L, Pred, B, A))
+    return AlwaysFalse;
+  Pred = ICmpInst::getSwappedPredicate(Pred);
+  if (SE->isLoopGuardedByCond(L, Pred, A, B))
+    return AlwaysTrue;
+  return Unknown;
+}
+
+enum SolverResult PointerTracking::checkLimits(const SCEV *Offset,
+                                               const SCEV *Limit,
+                                               BasicBlock *BB)
+{
+  //FIXME: merge implementation
+  return Unknown;
+}
+
+void PointerTracking::getPointerOffset(Value *Pointer, Value *&Base,
+                                       const SCEV *&Limit,
+                                       const SCEV *&Offset) const
+{
+    Pointer = Pointer->stripPointerCasts();
+    Base = Pointer->getUnderlyingObject();
+    Limit = getAllocationSizeInBytes(Base);
+    if (isa<SCEVCouldNotCompute>(Limit)) {
+      Base = 0;
+      Offset = Limit;
+      return;
+    }
+
+    Offset = SE->getMinusSCEV(SE->getSCEV(Pointer), SE->getSCEV(Base));
+    if (isa<SCEVCouldNotCompute>(Offset)) {
+      Base = 0;
+      Limit = Offset;
+    }
+}
+
+void PointerTracking::print(raw_ostream &OS, const Module* M) const {
+  // Calling some PT methods may cause caches to be updated, however
+  // this should be safe for the same reason its safe for SCEV.
+  PointerTracking &PT = *const_cast<PointerTracking*>(this);
+  for (inst_iterator I=inst_begin(*FF), E=inst_end(*FF); I != E; ++I) {
+    if (!isa<PointerType>(I->getType()))
+      continue;
+    Value *Base;
+    const SCEV *Limit, *Offset;
+    getPointerOffset(&*I, Base, Limit, Offset);
+    if (!Base)
+      continue;
+
+    if (Base == &*I) {
+      const SCEV *S = getAllocationElementCount(Base);
+      OS << *Base << " ==> " << *S << " elements, ";
+      OS << *Limit << " bytes allocated\n";
+      continue;
+    }
+    OS << &*I << " -- base: " << *Base;
+    OS << " offset: " << *Offset;
+
+    enum SolverResult res = PT.checkLimits(Offset, Limit, I->getParent());
+    switch (res) {
+    case AlwaysTrue:
+      OS << " always safe\n";
+      break;
+    case AlwaysFalse:
+      OS << " always unsafe\n";
+      break;
+    case Unknown:
+      OS << " <<unknown>>\n";
+      break;
+    }
+  }
+}
+
+void PointerTracking::print(std::ostream &o, const Module* M) const {
+  raw_os_ostream OS(o);
+  print(OS, M);
+}
+
+static RegisterPass<PointerTracking> X("pointertracking",
+                                       "Track pointer bounds", false, true);
+}