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Update comments about vector splat handling in x86

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137808 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bruno Cardoso Lopes 2011-08-17 02:29:13 +00:00
parent fc0a702128
commit 8a5b262e80
1 changed files with 7 additions and 8 deletions
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15
lib/Target/X86/X86ISelLowering.cpp
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@ -4205,8 +4205,7 @@ static SDValue getLegalSplat(SelectionDAG &DAG, SDValue V, int EltNo) {
return DAG.getNode(ISD::BITCAST, dl, VT, V);
}
/// PromoteSplat - Promote a splat of v4i32, v8i16 or v16i8 to v4f32 and
/// v8i32, v16i16 or v32i8 to v8f32.
/// PromoteSplat - Splat is promoted to target supported vector shuffles.
static SDValue PromoteSplat(ShuffleVectorSDNode *SV, SelectionDAG &DAG) {
EVT SrcVT = SV->getValueType(0);
SDValue V1 = SV->getOperand(0);
@ -4225,7 +4224,11 @@ static SDValue PromoteSplat(ShuffleVectorSDNode *SV, SelectionDAG &DAG) {
EltNo -= NumElems/2;
}
// Make this 128-bit vector duplicate i8 and i16 elements
// All i16 and i8 vector types can't be used directly by a generic shuffle
// instruction because the target has no such instruction. Generate shuffles
// which repeat i16 and i8 several times until they fit in i32, and then can
// be manipulated by target suported shuffles. After the insertion of the
// necessary shuffles, the result is bitcasted back to v4f32 or v8f32.
EVT EltVT = SrcVT.getVectorElementType();
if (NumElems > 4 && (EltVT == MVT::i8 || EltVT == MVT::i16))
V1 = PromoteSplati8i16(V1, DAG, EltNo);
@ -6175,11 +6178,7 @@ SDValue NormalizeVectorShuffle(SDValue Op, SelectionDAG &DAG,
if (VT.is128BitVector() && NumElem <= 4)
return SDValue();
// All i16 and i8 vector types can't be used directly by a generic shuffle
// instruction because the target has no such instruction. Generate shuffles
// which repeat i16 and i8 several times until they fit in i32, and then can
// be manipulated by target suported shuffles. After the insertion of the
// necessary shuffles, the result is bitcasted back to v4f32 or v8f32.
// All remaning splats are promoted to target supported vector shuffles.
return PromoteSplat(SVOp, DAG);
}