[SLP] Vectorize jumbled memory loads.

Summary:
This patch tries to vectorize loads of consecutive memory accesses, accessed
in non-consecutive or jumbled way. An earlier attempt was made with patch D26905
which was reverted back due to some basic issue with representing the 'use mask' of
jumbled accesses.

This patch fixes the mask representation by recording the 'use mask' in the usertree entry.

Change-Id: I9fe7f5045f065d84c126fa307ef6ebe0787296df

Reviewers: mkuper, loladiro, Ayal, zvi, danielcdh

Reviewed By: Ayal

Subscribers: mgrang, dcaballe, hans, mzolotukhin

Differential Revision: https://reviews.llvm.org/D36130

llvm-svn: 320548

1 files changed, 71 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index e141d6c58b6..ed8e5e8cc48 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1107,6 +1107,77 @@ static unsigned getAddressSpaceOperand(Value *I) {
   return -1;
 }
 
+// TODO:This API can be improved by using the permutation of given width as the
+// accesses are entered into the map.
+bool llvm::sortLoadAccesses(ArrayRef<Value *> VL, const DataLayout &DL,
+                           ScalarEvolution &SE,
+                           SmallVectorImpl<Value *> &Sorted,
+                           SmallVectorImpl<unsigned> *Mask) {
+  SmallVector<std::pair<int64_t, Value *>, 4> OffValPairs;
+  OffValPairs.reserve(VL.size());
+  Sorted.reserve(VL.size());
+
+  // Walk over the pointers, and map each of them to an offset relative to
+  // first pointer in the array.
+  Value *Ptr0 = getPointerOperand(VL[0]);
+  const SCEV *Scev0 = SE.getSCEV(Ptr0);
+  Value *Obj0 = GetUnderlyingObject(Ptr0, DL);
+  PointerType *PtrTy = dyn_cast<PointerType>(Ptr0->getType());
+  uint64_t Size = DL.getTypeAllocSize(PtrTy->getElementType());
+
+  for (auto *Val : VL) {
+    // The only kind of access we care about here is load.
+    if (!isa<LoadInst>(Val))
+      return false;
+
+    Value *Ptr = getPointerOperand(Val);
+    assert(Ptr && "Expected value to have a pointer operand.");
+    // If a pointer refers to a different underlying object, bail - the
+    // pointers are by definition incomparable.
+    Value *CurrObj = GetUnderlyingObject(Ptr, DL);
+    if (CurrObj != Obj0)
+      return false;
+
+    const SCEVConstant *Diff =
+        dyn_cast<SCEVConstant>(SE.getMinusSCEV(SE.getSCEV(Ptr), Scev0));
+    // The pointers may not have a constant offset from each other, or SCEV
+    // may just not be smart enough to figure out they do. Regardless,
+    // there's nothing we can do.
+    if (!Diff || static_cast<unsigned>(Diff->getAPInt().abs().getSExtValue()) >
+                     (VL.size() - 1) * Size)
+      return false;
+
+    OffValPairs.emplace_back(Diff->getAPInt().getSExtValue(), Val);
+  }
+  SmallVector<unsigned, 4> UseOrder(VL.size());
+  for (unsigned i = 0; i < VL.size(); i++) {
+    UseOrder[i] = i;
+  }
+
+  // Sort the memory accesses and keep the order of their uses in UseOrder.
+  std::sort(UseOrder.begin(), UseOrder.end(),
+            [&OffValPairs](unsigned Left, unsigned Right) {
+            return OffValPairs[Left].first < OffValPairs[Right].first;
+            });
+
+  for (unsigned i = 0; i < VL.size(); i++)
+    Sorted.emplace_back(OffValPairs[UseOrder[i]].second);
+
+  // Sort UseOrder to compute the Mask.
+  if (Mask) {
+    Mask->reserve(VL.size());
+    for (unsigned i = 0; i < VL.size(); i++)
+      Mask->emplace_back(i);
+    std::sort(Mask->begin(), Mask->end(),
+              [&UseOrder](unsigned Left, unsigned Right) {
+              return UseOrder[Left] < UseOrder[Right];
+              });
+  }
+
+  return true;
+}
+
+
 /// Returns true if the memory operations \p A and \p B are consecutive.
 bool llvm::isConsecutiveAccess(Value *A, Value *B, const DataLayout &DL,
                                ScalarEvolution &SE, bool CheckType) {