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SelectionDAG shuffle nodes do not allow operands with different numbers of 

elements than the result vector type.  So, when an instruction like:

%8 = shufflevector <2 x float> %4, <2 x float> %7, <4 x i32> <i32 1, i32 0, i32 3, i32 2>

is translated to a DAG, each operand is changed to a concat_vectors node that appends 2 undef elements.  That is:

shuffle [a,b], [c,d] is changed to:
shuffle [a,b,u,u], [c,d,u,u]

That's probably the right thing for x86 but for NEON, we'd much rather have:

shuffle [a,b,c,d], undef

Teach the DAG combiner how to do that transformation for ARM.  Radar 8597007.

llvm-svn: 117482
This commit is contained in:
Bob Wilson 2010-10-27 20:38:28 +00:00
parent 24c8b04d5f
commit c7334a146e
2 changed files with 73 additions and 0 deletions
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55
llvm/lib/Target/ARM/ARMISelLowering.cpp
View File

@ -460,6 +460,7 @@ ARMTargetLowering::ARMTargetLowering(TargetMachine &TM)
setTargetDAGCombine(ISD::ANY_EXTEND);
setTargetDAGCombine(ISD::SELECT_CC);
setTargetDAGCombine(ISD::BUILD_VECTOR);
setTargetDAGCombine(ISD::VECTOR_SHUFFLE);
}
computeRegisterProperties();
@ -4531,6 +4532,59 @@ static SDValue PerformBUILD_VECTORCombine(SDNode *N, SelectionDAG &DAG) {
return SDValue();
}
/// PerformVECTOR_SHUFFLECombine - Target-specific dag combine xforms for
/// ISD::VECTOR_SHUFFLE.
static SDValue PerformVECTOR_SHUFFLECombine(SDNode *N, SelectionDAG &DAG) {
// The LLVM shufflevector instruction does not require the shuffle mask
// length to match the operand vector length, but ISD::VECTOR_SHUFFLE does
// have that requirement. When translating to ISD::VECTOR_SHUFFLE, if the
// operands do not match the mask length, they are extended by concatenating
// them with undef vectors. That is probably the right thing for other
// targets, but for NEON it is better to concatenate two double-register
// size vector operands into a single quad-register size vector. Do that
// transformation here:
// shuffle(concat(v1, undef), concat(v2, undef)) ->
// shuffle(concat(v1, v2), undef)
SDValue Op0 = N->getOperand(0);
SDValue Op1 = N->getOperand(1);
if (Op0.getOpcode() != ISD::CONCAT_VECTORS ||
Op1.getOpcode() != ISD::CONCAT_VECTORS ||
Op0.getNumOperands() != 2 ||
Op1.getNumOperands() != 2)
return SDValue();
SDValue Concat0Op1 = Op0.getOperand(1);
SDValue Concat1Op1 = Op1.getOperand(1);
if (Concat0Op1.getOpcode() != ISD::UNDEF ||
Concat1Op1.getOpcode() != ISD::UNDEF)
return SDValue();
// Skip the transformation if any of the types are illegal.
const TargetLowering &TLI = DAG.getTargetLoweringInfo();
EVT VT = N->getValueType(0);
if (!TLI.isTypeLegal(VT) ||
!TLI.isTypeLegal(Concat0Op1.getValueType()) ||
!TLI.isTypeLegal(Concat1Op1.getValueType()))
return SDValue();
SDValue NewConcat = DAG.getNode(ISD::CONCAT_VECTORS, N->getDebugLoc(), VT,
Op0.getOperand(0), Op1.getOperand(0));
// Translate the shuffle mask.
SmallVector<int, 16> NewMask;
unsigned NumElts = VT.getVectorNumElements();
unsigned HalfElts = NumElts/2;
ShuffleVectorSDNode *SVN = cast<ShuffleVectorSDNode>(N);
for (unsigned n = 0; n < NumElts; ++n) {
int MaskElt = SVN->getMaskElt(n);
int NewElt = -1;
if (MaskElt < HalfElts)
NewElt = MaskElt;
else if (MaskElt >= NumElts && MaskElt < NumElts + HalfElts)
NewElt = HalfElts + MaskElt - NumElts;
NewMask.push_back(NewElt);
}
return DAG.getVectorShuffle(VT, N->getDebugLoc(), NewConcat,
DAG.getUNDEF(VT), NewMask.data());
}
/// PerformVDUPLANECombine - Target-specific dag combine xforms for
/// ARMISD::VDUPLANE.
static SDValue PerformVDUPLANECombine(SDNode *N, SelectionDAG &DAG) {
@ -4939,6 +4993,7 @@ SDValue ARMTargetLowering::PerformDAGCombine(SDNode *N,
case ARMISD::VMOVRRD: return PerformVMOVRRDCombine(N, DCI);
case ARMISD::VMOVDRR: return PerformVMOVDRRCombine(N, DCI.DAG);
case ISD::BUILD_VECTOR: return PerformBUILD_VECTORCombine(N, DCI.DAG);
case ISD::VECTOR_SHUFFLE: return PerformVECTOR_SHUFFLECombine(N, DCI.DAG);
case ARMISD::VDUPLANE: return PerformVDUPLANECombine(N, DCI.DAG);
case ISD::INTRINSIC_WO_CHAIN: return PerformIntrinsicCombine(N, DCI.DAG);
case ISD::SHL:

18
llvm/test/CodeGen/ARM/vrev.ll
View File

@ -129,3 +129,21 @@ define <8 x i16> @test_vrev32Q16_undef(<8 x i16>* %A) nounwind {
%tmp2 = shufflevector <8 x i16> %tmp1, <8 x i16> undef, <8 x i32> <i32 undef, i32 0, i32 undef, i32 2, i32 5, i32 4, i32 7, i32 undef>
ret <8 x i16> %tmp2
}
; A vcombine feeding a VREV should not obscure things. Radar 8597007.
define void @test_with_vcombine(<4 x float>* %v) nounwind {
;CHECK: test_with_vcombine:
;CHECK-NOT: vext
;CHECK: vrev64.32
%tmp1 = load <4 x float>* %v, align 16
%tmp2 = bitcast <4 x float> %tmp1 to <2 x double>
%tmp3 = extractelement <2 x double> %tmp2, i32 0
%tmp4 = bitcast double %tmp3 to <2 x float>
%tmp5 = extractelement <2 x double> %tmp2, i32 1
%tmp6 = bitcast double %tmp5 to <2 x float>
%tmp7 = fadd <2 x float> %tmp6, %tmp6
%tmp8 = shufflevector <2 x float> %tmp4, <2 x float> %tmp7, <4 x i32> <i32 1, i32 0, i32 3, i32 2>
store <4 x float> %tmp8, <4 x float>* %v, align 16
ret void
}