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improve comments in the unpcklps generating logic, introduce

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a new EltStride variable instead of reusing NumElems variable
for a non-obvious purpose.  No functionality change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112377 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-08-28 17:15:43 +00:00
parent 44edb0bd0c
commit 6e80e44926
1 changed files with 18 additions and 11 deletions
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29
lib/Target/X86/X86ISelLowering.cpp
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@ -4040,8 +4040,8 @@ static SDValue EltsFromConsecutiveLoads(EVT VT, SmallVectorImpl<SDValue> &Elts,
SDValue
X86TargetLowering::LowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG) const {
DebugLoc dl = Op.getDebugLoc();
// All zero's are handled with pxor in SSE2 and above, xorps in SSE1 and
// all one's are handled with pcmpeqd. In AVX, zero's are handled with
// All zero's are handled with pxor in SSE2 and above, xorps in SSE1.
// All one's are handled with pcmpeqd. In AVX, zero's are handled with
// vpxor in 128-bit and xor{pd,ps} in 256-bit, but no 256 version of pcmpeqd
// is present, so AllOnes is ignored.
if (ISD::isBuildVectorAllZeros(Op.getNode()) ||
@ -4288,18 +4288,25 @@ X86TargetLowering::LowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG) const {
return V[0];
}
// Otherwise, expand into a number of unpckl*
// e.g. for v4f32
// Otherwise, expand into a number of unpckl*, start by extending each of
// our (non-undef) elements to the full vector width with the element in the
// bottom slot of the vector (which generates no code for SSE).
for (unsigned i = 0; i < NumElems; ++i) {
if (Op.getOperand(i).getOpcode() != ISD::UNDEF)
V[i] = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, VT, Op.getOperand(i));
else
V[i] = DAG.getUNDEF(VT);
}
// Next, we iteratively mix elements, e.g. for v4f32:
// Step 1: unpcklps 0, 2 ==> X: <?, ?, 2, 0>
// : unpcklps 1, 3 ==> Y: <?, ?, 3, 1>
// Step 2: unpcklps X, Y ==> <3, 2, 1, 0>
for (unsigned i = 0; i < NumElems; ++i)
V[i] = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, VT, Op.getOperand(i));
NumElems >>= 1;
while (NumElems != 0) {
for (unsigned i = 0; i < NumElems; ++i)
V[i] = getUnpackl(DAG, dl, VT, V[i], V[i + NumElems]);
NumElems >>= 1;
unsigned EltStride = NumElems >> 1;
while (EltStride != 0) {
for (unsigned i = 0; i < EltStride; ++i)
V[i] = getUnpackl(DAG, dl, VT, V[i], V[i + EltStride]);
EltStride >>= 1;
}
return V[0];
}