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Per chris's request, add some comments.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99434 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nate Begeman 2010-03-24 22:19:06 +00:00
parent 9bb59a2bdc
commit 1449f29100
1 changed files with 17 additions and 2 deletions
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19
lib/Target/X86/X86ISelLowering.cpp
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@ -3613,14 +3613,26 @@ X86TargetLowering::LowerAsSplatVectorLoad(SDValue SrcOp, EVT VT, DebugLoc dl,
return SDValue();
}
/// EltsFromConsecutiveLoads - Given the initializing elements 'Elts' of a
/// vector of type 'VT', see if the elements can be replaced by a single large
/// load which has the same value as a build_vector whose operands are 'elts'.
///
/// Example: <load i32 *a, load i32 *a+4, undef, undef> -> zextload a
///
/// FIXME: we'd also like to handle the case where the last elements are zero
/// rather than undef via VZEXT_LOAD, but we do not detect that case today.
/// There's even a handy isZeroNode for that purpose.
static SDValue EltsFromConsecutiveLoads(EVT VT, SmallVectorImpl<SDValue> &Elts,
DebugLoc &dl, SelectionDAG &DAG) {
EVT EltVT = VT.getVectorElementType();
unsigned NumElems = Elts.size();
// FIXME: check for zeroes
LoadSDNode *LDBase = NULL;
unsigned LastLoadedElt = -1U;
// For each element in the initializer, see if we've found a load or an undef.
// If we don't find an initial load element, or later load elements are
// non-consecutive, bail out.
for (unsigned i = 0; i < NumElems; ++i) {
SDValue Elt = Elts[i];
@ -3642,7 +3654,10 @@ static SDValue EltsFromConsecutiveLoads(EVT VT, SmallVectorImpl<SDValue> &Elts,
return SDValue();
LastLoadedElt = i;
}
// If we have found an entire vector of loads and undefs, then return a large
// load of the entire vector width starting at the base pointer. If we found
// consecutive loads for the low half, generate a vzext_load node.
if (LastLoadedElt == NumElems - 1) {
if (DAG.InferPtrAlignment(LDBase->getBasePtr()) >= 16)
return DAG.getLoad(VT, dl, LDBase->getChain(), LDBase->getBasePtr(),