[LAA] Remove unused needsAnyChecking(), NFC

[oota-llvm.git] / lib / Analysis / LoopAccessAnalysis.cpp

diff --git a/lib/Analysis/LoopAccessAnalysis.cpp b/lib/Analysis/LoopAccessAnalysis.cpp
index 6a6b6d4be3bc4e8d77936f6034882a4c10ab705a..eca98cf011c7ee3ef7bfb15b3a8cbb332fe62233 100644 (file)
--- a/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/lib/Analysis/LoopAccessAnalysis.cpp
@@ -237,8 +237,31 @@ void RuntimePointerChecking::groupChecks(
 
   CheckingGroups.clear();
 
+  // If we need to check two pointers to the same underlying object
+  // with a non-constant difference, we shouldn't perform any pointer
+  // grouping with those pointers. This is because we can easily get
+  // into cases where the resulting check would return false, even when
+  // the accesses are safe.
+  //
+  // The following example shows this:
+  // for (i = 0; i < 1000; ++i)
+  //   a[5000 + i * m] = a[i] + a[i + 9000]
+  //
+  // Here grouping gives a check of (5000, 5000 + 1000 * m) against
+  // (0, 10000) which is always false. However, if m is 1, there is no
+  // dependence. Not grouping the checks for a[i] and a[i + 9000] allows
+  // us to perform an accurate check in this case.
+  //
+  // The above case requires that we have an UnknownDependence between
+  // accesses to the same underlying object. This cannot happen unless
+  // ShouldRetryWithRuntimeCheck is set, and therefore UseDependencies
+  // is also false. In this case we will use the fallback path and create
+  // separate checking groups for all pointers.
+ 
   // If we don't have the dependency partitions, construct a new
-  // checking pointer group for each pointer.
+  // checking pointer group for each pointer. This is also required
+  // for correctness, because in this case we can have checking between
+  // pointers to the same underlying object.
   if (!UseDependencies) {
     for (unsigned I = 0; I < Pointers.size(); ++I)
       CheckingGroups.push_back(CheckingPtrGroup(I, *this));
@@ -397,17 +420,6 @@ unsigned RuntimePointerChecking::getNumberOfChecks(
   return CheckCount;
 }
 
-bool RuntimePointerChecking::needsAnyChecking(
-    const SmallVectorImpl<int> *PtrPartition) const {
-  unsigned NumPointers = Pointers.size();
-
-  for (unsigned I = 0; I < NumPointers; ++I)
-    for (unsigned J = I + 1; J < NumPointers; ++J)
-      if (needsChecking(I, J, PtrPartition))
-        return true;
-  return false;
-}
-
 namespace {
 /// \brief Analyses memory accesses in a loop.
 ///
@@ -807,11 +819,11 @@ static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR,
 /// \brief Check whether the access through \p Ptr has a constant stride.
 int llvm::isStridedPtr(ScalarEvolution *SE, Value *Ptr, const Loop *Lp,
                        const ValueToValueMap &StridesMap) {
-  const Type *Ty = Ptr->getType();
+  Type *Ty = Ptr->getType();
   assert(Ty->isPointerTy() && "Unexpected non-ptr");
 
   // Make sure that the pointer does not point to aggregate types.
-  const PointerType *PtrTy = cast<PointerType>(Ty);
+  auto *PtrTy = cast<PointerType>(Ty);
   if (PtrTy->getElementType()->isAggregateType()) {
     DEBUG(dbgs() << "LAA: Bad stride - Not a pointer to a scalar type"
           << *Ptr << "\n");