When performing a truncating store, it's possible to rearrange the data

in-register, such that we can use a single vector store rather then a 
series of scalar stores.

For func_4_8 the generated code

	vldr	d16, LCPI0_0
	vmov	d17, r0, r1
	vadd.i16	d16, d17, d16
	vmov.u16	r0, d16[3]
	strb	r0, [r2, #3]
	vmov.u16	r0, d16[2]
	strb	r0, [r2, #2]
	vmov.u16	r0, d16[1]
	strb	r0, [r2, #1]
	vmov.u16	r0, d16[0]
	strb	r0, [r2]
	bx	lr

becomes

	vldr	d16, LCPI0_0
	vmov	d17, r0, r1
	vadd.i16	d16, d17, d16
	vuzp.8	d16, d17
	vst1.32	{d16[0]}, [r2, :32]
	bx	lr

I'm not fond of how this combine pessimizes 2012-03-13-DAGCombineBug.ll,
but I couldn't think of a way to judiciously apply this combine.

This

	ldrh	r0, [r0, #4]
	strh	r0, [r1]

becomes

	vldr	d16, [r0]
	vmov.u16	r0, d16[2]
	vmov.32	d16[0], r0
	vuzp.16	d16, d17
	vst1.32	{d16[0]}, [r1, :32]

PR11158
rdar://10703339


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154340 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMISelLowering.cpp

@@ -7339,8 +7339,92 @@ static SDValue PerformVMOVDRRCombine(SDNode *N, SelectionDAG &DAG) {
 static SDValue PerformSTORECombine(SDNode *N,
                                    TargetLowering::DAGCombinerInfo &DCI) {
   StoreSDNode *St = cast<StoreSDNode>(N);
+  if (St->isVolatile())
+    return SDValue();
+
+  // Optimize trunc store (of multiple scalars) to shuffle and store.  First, 
+  // pack all of the elements in one place.  Next, store to memory in fewer
+  // chunks.
   SDValue StVal = St->getValue();
-  if (!ISD::isNormalStore(St) || St->isVolatile())
+  EVT VT = StVal.getValueType();
+  if (St->isTruncatingStore() && VT.isVector()) {
+    SelectionDAG &DAG = DCI.DAG;
+    const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+    EVT StVT = St->getMemoryVT();
+    unsigned NumElems = VT.getVectorNumElements();
+    assert(StVT != VT && "Cannot truncate to the same type");
+    unsigned FromEltSz = VT.getVectorElementType().getSizeInBits();
+    unsigned ToEltSz = StVT.getVectorElementType().getSizeInBits();
+
+    // From, To sizes and ElemCount must be pow of two
+    if (!isPowerOf2_32(NumElems * FromEltSz * ToEltSz)) return SDValue();
+
+    // We are going to use the original vector elt for storing.
+    // Accumulated smaller vector elements must be a multiple of the store size.
+    if (0 != (NumElems * FromEltSz) % ToEltSz) return SDValue();
+
+    unsigned SizeRatio  = FromEltSz / ToEltSz;
+    assert(SizeRatio * NumElems * ToEltSz == VT.getSizeInBits());
+
+    // Create a type on which we perform the shuffle.
+    EVT WideVecVT = EVT::getVectorVT(*DAG.getContext(), StVT.getScalarType(),
+                                     NumElems*SizeRatio);
+    assert(WideVecVT.getSizeInBits() == VT.getSizeInBits());
+
+    DebugLoc DL = St->getDebugLoc();
+    SDValue WideVec = DAG.getNode(ISD::BITCAST, DL, WideVecVT, StVal);
+    SmallVector<int, 8> ShuffleVec(NumElems * SizeRatio, -1);
+    for (unsigned i = 0; i < NumElems; ++i) ShuffleVec[i] = i * SizeRatio;
+
+    // Can't shuffle using an illegal type.
+    if (!TLI.isTypeLegal(WideVecVT)) return SDValue();
+
+    SDValue Shuff = DAG.getVectorShuffle(WideVecVT, DL, WideVec,
+                                DAG.getUNDEF(WideVec.getValueType()),
+                                ShuffleVec.data());
+    // At this point all of the data is stored at the bottom of the
+    // register. We now need to save it to mem.
+
+    // Find the largest store unit
+    MVT StoreType = MVT::i8;
+    for (unsigned tp = MVT::FIRST_INTEGER_VALUETYPE;
+         tp < MVT::LAST_INTEGER_VALUETYPE; ++tp) {
+      MVT Tp = (MVT::SimpleValueType)tp;
+      if (TLI.isTypeLegal(Tp) && Tp.getSizeInBits() <= NumElems * ToEltSz)
+        StoreType = Tp;
+    }
+    // Didn't find a legal store type.
+    if (!TLI.isTypeLegal(StoreType))
+      return SDValue();
+
+    // Bitcast the original vector into a vector of store-size units
+    EVT StoreVecVT = EVT::getVectorVT(*DAG.getContext(),
+            StoreType, VT.getSizeInBits()/EVT(StoreType).getSizeInBits());
+    assert(StoreVecVT.getSizeInBits() == VT.getSizeInBits());
+    SDValue ShuffWide = DAG.getNode(ISD::BITCAST, DL, StoreVecVT, Shuff);
+    SmallVector<SDValue, 8> Chains;
+    SDValue Increment = DAG.getConstant(StoreType.getSizeInBits()/8,
+                                        TLI.getPointerTy());
+    SDValue BasePtr = St->getBasePtr();
+
+    // Perform one or more big stores into memory.
+    unsigned E = (ToEltSz*NumElems)/StoreType.getSizeInBits();
+    for (unsigned I = 0; I < E; I++) {
+      SDValue SubVec = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL,
+                                   StoreType, ShuffWide,
+                                   DAG.getIntPtrConstant(I));
+      SDValue Ch = DAG.getStore(St->getChain(), DL, SubVec, BasePtr,
+                                St->getPointerInfo(), St->isVolatile(),
+                                St->isNonTemporal(), St->getAlignment());
+      BasePtr = DAG.getNode(ISD::ADD, DL, BasePtr.getValueType(), BasePtr,
+                            Increment);
+      Chains.push_back(Ch);
+    }
+    return DAG.getNode(ISD::TokenFactor, DL, MVT::Other, &Chains[0],
+                       Chains.size());
+  }
+
+  if (!ISD::isNormalStore(St))
     return SDValue();
 
   // Split a store of a VMOVDRR into two integer stores to avoid mixing NEON and

test/CodeGen/ARM/2012-03-13-DAGCombineBug.ll

@@ -6,8 +6,7 @@
 ; (i32 extload $addr+c*sizeof(i16)
 define void @test_hi_short3(<3 x i16> * nocapture %srcA, <2 x i16> * nocapture %dst) nounwind {
 entry:
-; CHECK: ldrh [[REG:r[0-9]+]]
-; CHECK: strh [[REG]]
+; CHECK: vst1.32
   %0 = load <3 x i16> * %srcA, align 8
   %1 = shufflevector <3 x i16> %0, <3 x i16> undef, <2 x i32> <i32 2, i32 undef>
   store <2 x i16> %1, <2 x i16> * %dst, align 4

test/CodeGen/ARM/opt-shuff-tstore.ll

@@ -0,0 +1,19 @@
+; RUN: llc -mcpu=cortex-a9 -mtriple=arm-linux-unknown -promote-elements -mattr=+neon < %s | FileCheck %s
+
+; CHECK: func_4_8
+; CHECK: vst1.32
+; CHECK-NEXT: bx lr
+define void @func_4_8(<4 x i8> %param, <4 x i8>* %p) {
+  %r = add <4 x i8> %param, <i8 1, i8 2, i8 3, i8 4>
+  store <4 x i8> %r, <4 x i8>* %p
+  ret void
+}
+
+; CHECK: func_2_16
+; CHECK: vst1.32
+; CHECK-NEXT: bx lr
+define void @func_2_16(<2 x i16> %param, <2 x i16>* %p) {
+  %r = add <2 x i16> %param, <i16 1, i16 2>
+  store <2 x i16> %r, <2 x i16>* %p
+  ret void
+}

test/CodeGen/ARM/vrev.ll

@@ -149,12 +149,10 @@ define void @test_with_vcombine(<4 x float>* %v) nounwind {
 }
 
 ; The type <2 x i16> is legalized to <2 x i32> and need to be trunc-stored
-; to <2 x i16> when stored to memory. Currently ARM scalarizes these stores.
-; See PR 11158
+; to <2 x i16> when stored to memory.
 define void @test_vrev64(<4 x i16>* nocapture %source, <2 x i16>* nocapture %dst) nounwind ssp {
 ; CHECK: test_vrev64:
-; CHECK: vst1.16
-; CHECK: vst1.16
+; CHECK: vst1.32
 entry:
   %0 = bitcast <4 x i16>* %source to <8 x i16>*
   %tmp2 = load <8 x i16>* %0, align 4