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add a minor dag combine noticed when looking at PR945 

llvm-svn: 30915
This commit is contained in:
Chris Lattner 2006-10-12 20:23:19 +00:00
parent a7956d2894
commit 2e33fb453b
1 changed files with 7 additions and 0 deletions
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7
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -1664,6 +1664,13 @@ SDOperand DAGCombiner::visitSRL(SDNode *N) {
return DAG.getNode(ISD::ANY_EXTEND, VT, SmallShift);
}
// fold (srl (sra X, Y), 31) -> (srl X, 31). This srl only looks at the sign
// bit, which is unmodified by sra.
if (N1C && N1C->getValue()+1 == MVT::getSizeInBits(VT)) {
if (N0.getOpcode() == ISD::SRA)
return DAG.getNode(ISD::SRL, VT, N0.getOperand(0), N1);
}
// fold (srl (ctlz x), "5") -> x iff x has one bit set (the low bit).
if (N1C && N0.getOpcode() == ISD::CTLZ &&
N1C->getValue() == Log2_32(MVT::getSizeInBits(VT))) {