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Check even more carefully before applying this DAGCombine transform. 

llvm-svn: 48580
This commit is contained in:
Christopher Lamb 2008-03-20 04:31:39 +00:00
parent 80e43fa744
commit 3e9f49716e
1 changed files with 19 additions and 13 deletions
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32
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -2386,27 +2386,33 @@ SDOperand DAGCombiner::visitSRA(SDNode *N) {
// fold sra (shl X, m), result_size - n
// -> (sign_extend (trunc (shl X, result_size - n - m))) for
// result_size - n != m. If truncate is free for the target sext(shl) is
// likely to result in better code.
// result_size - n != m.
// If truncate is free for the target sext(shl) is likely to result in better
// code.
if (N0.getOpcode() == ISD::SHL) {
// Get the two constanst of the shifts, CN0 = m, CN = n.
const ConstantSDNode *N01C = dyn_cast<ConstantSDNode>(N0.getOperand(1));
if (N01C && N1C) {
// Determine if the truncate type's bitsize would correspond to
// an integer type for this target.
// Determine what the truncate's result bitsize and type would be.
unsigned VTValSize = MVT::getSizeInBits(VT);
MVT::ValueType TruncVT = MVT::getIntegerType(VTValSize - N1C->getValue());
// Determine the residual right-shift amount.
unsigned ShiftAmt = N1C->getValue() - N01C->getValue();
// If the shift wouldn't be a noop, the truncated type is an actual type,
// and the truncate is free, then proceed with the transform.
if (ShiftAmt != 0 &&
TLI.isTypeLegal(TruncVT) &&
// If the shift is not a no-op (in which case this should be just a sign
// extend already), the truncated to type is legal, sign_extend is legal
// on that type, and the the truncate to that type is both legal and free,
// perform the transform.
if (ShiftAmt &&
TLI.isTypeLegal(TruncVT) &&
TLI.isOperationLegal(ISD::SIGN_EXTEND, TruncVT) &&
TLI.isOperationLegal(ISD::TRUNCATE, VT) &&
TLI.isTruncateFree(VT, TruncVT)) {
SDOperand Amt = DAG.getConstant(ShiftAmt, TLI.getShiftAmountTy());
SDOperand Shift = DAG.getNode(ISD::SRL, VT, N0.getOperand(0), Amt);
SDOperand Trunc = DAG.getNode(ISD::TRUNCATE, TruncVT, Shift);
return DAG.getNode(ISD::SIGN_EXTEND, N->getValueType(0), Trunc);
SDOperand Amt = DAG.getConstant(ShiftAmt, TLI.getShiftAmountTy());
SDOperand Shift = DAG.getNode(ISD::SRL, VT, N0.getOperand(0), Amt);
SDOperand Trunc = DAG.getNode(ISD::TRUNCATE, TruncVT, Shift);
return DAG.getNode(ISD::SIGN_EXTEND, N->getValueType(0), Trunc);
}
}
}