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[SelectionDAG] fold concat of extract subvectors

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This is derived from the related fold for build vectors.
We also have a version of this in DAGCombiner. The benefit of
having this fold at node creation time is (1) efficiency and
(2) preventing infinite looping from creating patterns that
should not exist in the first place.

Currently, the inf-loop could happen with MergeConsecutiveStores()
because it naively creates concat of extracts when forming a wider
vector store. That could fight with target-specific store narrowing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@361780 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel 2019-05-27 20:26:21 +00:00
parent 072973eb9b
commit 5a8a6ab113
1 changed files with 25 additions and 0 deletions
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25
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -4160,6 +4160,31 @@ static SDValue foldCONCAT_VECTORS(const SDLoc &DL, EVT VT,
if (llvm::all_of(Ops, [](SDValue Op) { return Op.isUndef(); })) if (llvm::all_of(Ops, [](SDValue Op) { return Op.isUndef(); }))
return DAG.getUNDEF(VT); return DAG.getUNDEF(VT);
// Scan the operands and look for extract operations from a single source
// that correspond to insertion at the same location via this concatenation:
// concat (extract X, 0*subvec_elts), (extract X, 1*subvec_elts), ...
SDValue IdentitySrc;
bool IsIdentity = true;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
SDValue Op = Ops[i];
unsigned IdentityIndex = i * Op.getValueType().getVectorNumElements();
if (Op.getOpcode() != ISD::EXTRACT_SUBVECTOR ||
Op.getOperand(0).getValueType() != VT ||
(IdentitySrc && Op.getOperand(0) != IdentitySrc) ||
!isa<ConstantSDNode>(Op.getOperand(1)) ||
Op.getConstantOperandVal(1) != IdentityIndex) {
IsIdentity = false;
break;
}
assert((!IdentitySrc || IdentitySrc == Op.getOperand(0)) &&
"Unexpected identity source vector for concat of extracts");
IdentitySrc = Op.getOperand(0);
}
if (IsIdentity) {
assert(IdentitySrc && "Failed to set source vector of extracts");
return IdentitySrc;
}
// A CONCAT_VECTOR with all UNDEF/BUILD_VECTOR operands can be // A CONCAT_VECTOR with all UNDEF/BUILD_VECTOR operands can be
// simplified to one big BUILD_VECTOR. // simplified to one big BUILD_VECTOR.
// FIXME: Add support for SCALAR_TO_VECTOR as well. // FIXME: Add support for SCALAR_TO_VECTOR as well.