[SystemZ] Rework getInterleavedMemoryOpCost()

Model this function more closely after the BasicTTIImpl version, with
separate handling of loads and stores. For loads, the set of actually loaded
vectors is checked.

This makes it more readable and just slightly more accurate generally.

Review: Ulrich Weigand
https://reviews.llvm.org/D53071

llvm-svn: 345998

1 files changed, 48 insertions, 16 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
index e7052e2e469..279a8218b1c 100644
--- a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
@@ -979,6 +979,11 @@ int SystemZTTIImpl::getMemoryOpCost(unsigned Opcode, Type *Src,
   return  NumOps;
 }
 
+// The generic implementation of getInterleavedMemoryOpCost() is based on
+// adding costs of the memory operations plus all the extracts and inserts
+// needed for using / defining the vector operands. The SystemZ version does
+// roughly the same but bases the computations on vector permutations
+// instead.
 int SystemZTTIImpl::getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy,
                                                unsigned Factor,
                                                ArrayRef<unsigned> Indices,
@@ -993,22 +998,49 @@ int SystemZTTIImpl::getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy,
   assert(isa<VectorType>(VecTy) &&
          "Expect a vector type for interleaved memory op");
 
-  int NumWideParts = getNumVectorRegs(VecTy);
-
-  // How many source vectors are handled to produce a vectorized operand?
-  int NumElsPerVector = (VecTy->getVectorNumElements() / NumWideParts);
-  int NumSrcParts =
-    ((NumWideParts > NumElsPerVector) ? NumElsPerVector : NumWideParts);
-
-  // A Load group may have gaps.
-  unsigned NumOperands =
-    ((Opcode == Instruction::Load) ? Indices.size() : Factor);
-
-  // Each needed permute takes two vectors as input.
-  if (NumSrcParts > 1)
-    NumSrcParts--;
-  int NumPermutes = NumSrcParts * NumOperands;
+  // Return the ceiling of dividing A by B.
+  auto ceil = [](unsigned A, unsigned B) { return (A + B - 1) / B; };
+
+  unsigned NumElts = VecTy->getVectorNumElements();
+  assert(Factor > 1 && NumElts % Factor == 0 && "Invalid interleave factor");
+  unsigned VF = NumElts / Factor;
+  unsigned NumEltsPerVecReg = (128U / getScalarSizeInBits(VecTy));
+  unsigned NumVectorMemOps = getNumVectorRegs(VecTy);
+  unsigned NumPermutes = 0;
+
+  if (Opcode == Instruction::Load) {
+    // Loading interleave groups may have gaps, which may mean fewer
+    // loads. Find out how many vectors will be loaded in total, and in how
+    // many of them each value will be in.
+    BitVector UsedInsts(NumVectorMemOps, false);
+    std::vector<BitVector> ValueVecs(Factor, BitVector(NumVectorMemOps, false));
+    for (unsigned Index : Indices)
+      for (unsigned Elt = 0; Elt < VF; ++Elt) {
+        unsigned Vec = (Index + Elt * Factor) / NumEltsPerVecReg;
+        UsedInsts.set(Vec);
+        ValueVecs[Index].set(Vec);
+      }
+    NumVectorMemOps = UsedInsts.count();
+
+    for (unsigned Index : Indices) {
+      // Estimate that each loaded source vector containing this Index
+      // requires one operation, except that vperm can handle two input
+      // registers first time for each dst vector.
+      unsigned NumSrcVecs = ValueVecs[Index].count();
+      unsigned NumDstVecs = ceil(VF * getScalarSizeInBits(VecTy), 128U);
+      assert (NumSrcVecs >= NumDstVecs && "Expected at least as many sources");
+      NumPermutes += std::max(1U, NumSrcVecs - NumDstVecs);
+    }
+  } else {
+    // Estimate the permutes for each stored vector as the smaller of the
+    // number of elements and the number of source vectors. Subtract one per
+    // dst vector for vperm (S.A.).
+    unsigned NumSrcVecs = std::min(NumEltsPerVecReg, Factor);
+    unsigned NumDstVecs = NumVectorMemOps;
+    assert (NumSrcVecs > 1 && "Expected at least two source vectors.");
+    NumPermutes += (NumDstVecs * NumSrcVecs) - NumDstVecs;
+  }
 
   // Cost of load/store operations and the permutations needed.
-  return NumWideParts + NumPermutes;
+  return NumVectorMemOps + NumPermutes;
 }