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[DAG] visitShiftByConstant - replace constant detection with FoldConstantArithmetic

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Instead of checking that an operand is constant/opaque before calling getNode() and then checking that the result is a constant, just use FoldConstantArithmetic which will just early-out if the operands are not constant foldable.
This commit is contained in:
Simon Pilgrim 2022-10-17 16:19:02 +01:00
parent 45cadb4bd3
commit 8e77458578
1 changed files with 8 additions and 12 deletions
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20
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -8880,11 +8880,6 @@ SDValue DAGCombiner::visitShiftByConstant(SDNode *N) {
break;
}
// We require the RHS of the binop to be a constant and not opaque as well.
ConstantSDNode *BinOpCst = getAsNonOpaqueConstant(LHS.getOperand(1));
if (!BinOpCst)
return SDValue();
// FIXME: disable this unless the input to the binop is a shift by a constant
// or is copy/select. Enable this in other cases when figure out it's exactly
// profitable.
@ -8902,16 +8897,17 @@ SDValue DAGCombiner::visitShiftByConstant(SDNode *N) {
if (IsCopyOrSelect && N->hasOneUse())
return SDValue();
// Fold the constants, shifting the binop RHS by the shift amount.
// Attempt to fold the constants, shifting the binop RHS by the shift amount.
SDLoc DL(N);
EVT VT = N->getValueType(0);
SDValue NewRHS = DAG.getNode(N->getOpcode(), DL, VT, LHS.getOperand(1),
N->getOperand(1));
assert(isa<ConstantSDNode>(NewRHS) && "Folding was not successful!");
if (SDValue NewRHS = DAG.FoldConstantArithmetic(
N->getOpcode(), DL, VT, {LHS.getOperand(1), N->getOperand(1)})) {
SDValue NewShift = DAG.getNode(N->getOpcode(), DL, VT, LHS.getOperand(0),
N->getOperand(1));
return DAG.getNode(LHS.getOpcode(), DL, VT, NewShift, NewRHS);
}
SDValue NewShift = DAG.getNode(N->getOpcode(), DL, VT, LHS.getOperand(0),
N->getOperand(1));
return DAG.getNode(LHS.getOpcode(), DL, VT, NewShift, NewRHS);
return SDValue();
}
SDValue DAGCombiner::distributeTruncateThroughAnd(SDNode *N) {