Fix X86's isTruncateFree to not claim that truncate to i1 is free. This fixes Bill's testcase that failed for r48491.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48542 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Christopher Lamb
2008-03-19 08:30:06 +00:00
parent e6d5d39c07
commit 15cbde3cf6
4 changed files with 27 additions and 47 deletions

View File

@@ -2383,6 +2383,31 @@ SDOperand DAGCombiner::visitSRA(SDNode *N) {
DAG.getConstant(Sum, N1C->getValueType(0)));
}
}
// 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.
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.
unsigned VTValSize = MVT::getSizeInBits(VT);
MVT::ValueType TruncVT = MVT::getIntegerType(VTValSize - N1C->getValue());
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.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);
}
}
}
// Simplify, based on bits shifted out of the LHS.
if (N1C && SimplifyDemandedBits(SDOperand(N, 0)))