From 1449f29100a0d3950a1a17e962f7cf718198e283 Mon Sep 17 00:00:00 2001 From: Nate Begeman Date: Wed, 24 Mar 2010 22:19:06 +0000 Subject: [PATCH] Per chris's request, add some comments. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@99434 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/X86/X86ISelLowering.cpp | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp index 960655806b7..75e6f505484 100644 --- a/lib/Target/X86/X86ISelLowering.cpp +++ b/lib/Target/X86/X86ISelLowering.cpp @@ -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: -> 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 &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 &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(), -- 2.11.0