[SystemZ] Use "STC;MVC" for memset

Use "STC;MVC" for memsets that are too big for two STCs or MV...Is yet
small enough for a single MVC.  As with memcpy, I'm leaving longer cases
till later.

The number of tests might seem excessive, but f33 & f34 from memset-04.ll
failed the first cut because I'd not added the "?:" on the calculation
of Size1.

llvm-svn: 185918

1 files changed, 81 insertions, 0 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp b/llvm/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
index d2da9d2a03a..4ca9292092d 100644
--- a/llvm/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
@@ -44,3 +44,84 @@ EmitTargetCodeForMemcpy(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
   }
   return SDValue();
 }
+
+// Handle a memset of 1, 2, 4 or 8 bytes with the operands given by
+// Chain, Dst, ByteVal and Size.  These cases are expected to use
+// MVI, MVHHI, MVHI and MVGHI respectively.
+static SDValue memsetStore(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
+                           SDValue Dst, uint64_t ByteVal, uint64_t Size,
+                           unsigned Align,
+                           MachinePointerInfo DstPtrInfo) {
+  uint64_t StoreVal = ByteVal;
+  for (unsigned I = 1; I < Size; ++I)
+    StoreVal |= ByteVal << (I * 8);
+  return DAG.getStore(Chain, DL,
+                      DAG.getConstant(StoreVal, MVT::getIntegerVT(Size * 8)),
+                      Dst, DstPtrInfo, false, false, Align);
+}
+
+SDValue SystemZSelectionDAGInfo::
+EmitTargetCodeForMemset(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
+                        SDValue Dst, SDValue Byte, SDValue Size,
+                        unsigned Align, bool IsVolatile,
+                        MachinePointerInfo DstPtrInfo) const {
+  EVT DstVT = Dst.getValueType();
+
+  if (IsVolatile)
+    return SDValue();
+
+  if (ConstantSDNode *CSize = dyn_cast<ConstantSDNode>(Size)) {
+    uint64_t Bytes = CSize->getZExtValue();
+    if (Bytes == 0)
+      return SDValue();
+    if (ConstantSDNode *CByte = dyn_cast<ConstantSDNode>(Byte)) {
+      // Handle cases that can be done using at most two of
+      // MVI, MVHI, MVHHI and MVGHI.  The latter two can only be
+      // used if ByteVal is all zeros or all ones; in other casees,
+      // we can move at most 2 halfwords.
+      uint64_t ByteVal = CByte->getZExtValue();
+      if (ByteVal == 0 || ByteVal == 255 ?
+          Bytes <= 16 && CountPopulation_64(Bytes) <= 2 :
+          Bytes <= 4) {
+        unsigned Size1 = Bytes == 16 ? 8 : 1 << findLastSet(Bytes);
+        unsigned Size2 = Bytes - Size1;
+        SDValue Chain1 = memsetStore(DAG, DL, Chain, Dst, ByteVal, Size1,
+                                     Align, DstPtrInfo);
+        if (Size2 == 0)
+          return Chain1;
+        Dst = DAG.getNode(ISD::ADD, DL, DstVT, Dst,
+                          DAG.getConstant(Size1, DstVT));
+        DstPtrInfo = DstPtrInfo.getWithOffset(Size1);
+        SDValue Chain2 = memsetStore(DAG, DL, Chain, Dst, ByteVal, Size2,
+                                     std::min(Align, Size1), DstPtrInfo);
+        return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
+      }
+    } else {
+      // Handle one and two bytes using STC.
+      if (Bytes <= 2) {
+        SDValue Chain1 = DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo,
+                                      false, false, Align);
+        if (Bytes == 1)
+          return Chain1;
+        SDValue Dst2 = DAG.getNode(ISD::ADD, DL, DstVT, Dst,
+                                   DAG.getConstant(1, DstVT));
+        SDValue Chain2 = DAG.getStore(Chain, DL, Byte, Dst2,
+                                      DstPtrInfo.getWithOffset(1),
+                                      false, false, 1);
+        return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, Chain1, Chain2);
+      }
+    }
+    assert(Bytes >= 2 && "Should have dealt with 0- and 1-byte cases already");
+    if (Bytes <= 0x101) {
+      // Copy the byte to the first location and then use MVC to copy
+      // it to the rest.
+      Chain = DAG.getStore(Chain, DL, Byte, Dst, DstPtrInfo,
+                           false, false, Align);
+      SDValue Dst2 = DAG.getNode(ISD::ADD, DL, DstVT, Dst,
+                                 DAG.getConstant(1, DstVT));
+      return DAG.getNode(SystemZISD::MVC, DL, MVT::Other, Chain, Dst2, Dst,
+                         DAG.getConstant(Bytes - 1, MVT::i32));
+    }
+  }
+  return SDValue();
+}