[llvm] r174929 - ARM NEON: Handle v16i8 and v8i16 reverse shuffles

[Arnold Schwaighofer]

Author: arnolds
Date: Mon Feb 11 19:58:32 2013
New Revision: 174929

URL: http://llvm.org/viewvc/llvm-project?rev=174929&view=rev
Log:
ARM NEON: Handle v16i8 and v8i16 reverse shuffles

Lower reverse shuffles to a vrev64 and a vext instruction instead of the default
legalization of storing and loading to the stack. This is important because we
generate reverse shuffles in the loop vectorizer when we reverse store to an
array.

  uint8_t Arr[N];
  for (i = 0; i < N; ++i)
    Arr[N - i - 1] = ...

radar://13171760

Modified:
    llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
    llvm/trunk/test/CodeGen/ARM/vector-DAGCombine.ll

Modified: llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp?rev=174929&r1=174928&r2=174929&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp Mon Feb 11 19:58:32 2013
@@ -4294,6 +4294,21 @@ static bool isVZIP_v_undef_Mask(ArrayRef
   return true;
 }
 
+/// \return true if this is a reverse operation on an vector.
+static bool isReverseMask(ArrayRef<int> M, EVT VT) {
+  unsigned NumElts = VT.getVectorNumElements();
+  // Make sure the mask has the right size.
+  if (NumElts != M.size())
+      return false;
+
+  // Look for <15, ..., 3, -1, 1, 0>.
+  for (unsigned i = 0; i != NumElts; ++i)
+    if (M[i] >= 0 && M[i] != (int) (NumElts - 1 - i))
+      return false;
+
+  return true;
+}
+
 // If N is an integer constant that can be moved into a register in one
 // instruction, return an SDValue of such a constant (will become a MOV
 // instruction).  Otherwise return null.
@@ -4689,7 +4704,8 @@ ARMTargetLowering::isShuffleMaskLegal(co
           isVZIPMask(M, VT, WhichResult) ||
           isVTRN_v_undef_Mask(M, VT, WhichResult) ||
           isVUZP_v_undef_Mask(M, VT, WhichResult) ||
-          isVZIP_v_undef_Mask(M, VT, WhichResult));
+          isVZIP_v_undef_Mask(M, VT, WhichResult) ||
+          ((VT == MVT::v8i16 || VT == MVT::v16i8) && isReverseMask(M, VT)));
 }
 
 /// GeneratePerfectShuffle - Given an entry in the perfect-shuffle table, emit
@@ -4793,6 +4809,23 @@ static SDValue LowerVECTOR_SHUFFLEv8i8(S
                                  &VTBLMask[0], 8));
 }
 
+static SDValue LowerReverse_VECTOR_SHUFFLEv16i8_v8i16(SDValue Op,
+                                                      SelectionDAG &DAG) {
+  DebugLoc DL = Op.getDebugLoc();
+  SDValue OpLHS = Op.getOperand(0);
+  EVT VT = OpLHS.getValueType();
+
+  assert((VT == MVT::v8i16 || VT == MVT::v16i8) &&
+         "Expect an v8i16/v16i8 type");
+  OpLHS = DAG.getNode(ARMISD::VREV64, DL, VT, OpLHS);
+  // For a v16i8 type: After the VREV, we have got <8, ...15, 8, ..., 0>. Now,
+  // extract the first 8 bytes into the top double word and the last 8 bytes
+  // into the bottom double word. The v8i16 case is similar.
+  unsigned ExtractNum = (VT == MVT::v16i8) ? 8 : 4;
+  return DAG.getNode(ARMISD::VEXT, DL, VT, OpLHS, OpLHS,
+                     DAG.getConstant(ExtractNum, MVT::i32));
+}
+
 static SDValue LowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG) {
   SDValue V1 = Op.getOperand(0);
   SDValue V2 = Op.getOperand(1);
@@ -4930,6 +4963,9 @@ static SDValue LowerVECTOR_SHUFFLE(SDVal
     return DAG.getNode(ISD::BITCAST, dl, VT, Val);
   }
 
+  if ((VT == MVT::v8i16 || VT == MVT::v16i8) && isReverseMask(ShuffleMask, VT))
+    return LowerReverse_VECTOR_SHUFFLEv16i8_v8i16(Op, DAG);
+
   if (VT == MVT::v8i8) {
     SDValue NewOp = LowerVECTOR_SHUFFLEv8i8(Op, ShuffleMask, DAG);
     if (NewOp.getNode())

Modified: llvm/trunk/test/CodeGen/ARM/vector-DAGCombine.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/vector-DAGCombine.ll?rev=174929&r1=174928&r2=174929&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/vector-DAGCombine.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/vector-DAGCombine.ll Mon Feb 11 19:58:32 2013
@@ -133,3 +133,30 @@ define i16 @foldBuildVectors() {
   %3 = extractelement <8 x i16> %2, i32 0
   ret i16 %3
 }
+
+; Test that we are generating vrev and vext for reverse shuffles of v8i16
+; shuffles.
+; CHECK: reverse_v8i16
+define void @reverse_v8i16(<8 x i16>* %loadaddr, <8 x i16>* %storeaddr) {
+  %v0 = load <8 x i16>* %loadaddr
+  ; CHECK: vrev64.16
+  ; CHECK: vext.16
+  %v1 = shufflevector <8 x i16> %v0, <8 x i16> undef,
+              <8 x i32> <i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0>
+  store <8 x i16> %v1, <8 x i16>* %storeaddr
+  ret void
+}
+
+; Test that we are generating vrev and vext for reverse shuffles of v16i8
+; shuffles.
+; CHECK: reverse_v16i8
+define void @reverse_v16i8(<16 x i8>* %loadaddr, <16 x i8>* %storeaddr) {
+  %v0 = load <16 x i8>* %loadaddr
+  ; CHECK: vrev64.8
+  ; CHECK: vext.8
+  %v1 = shufflevector <16 x i8> %v0, <16 x i8> undef,
+       <16 x i32> <i32 15, i32 14, i32 13, i32 12, i32 11, i32 10, i32 9, i32 8,
+                   i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0>
+  store <16 x i8> %v1, <16 x i8>* %storeaddr
+  ret void
+}