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Know some simple identities. This improves codegen for (1LL << N). 

llvm-svn: 19698
This commit is contained in:
Chris Lattner 2005-01-19 17:29:49 +00:00
parent 474aac4da9
commit 32a5f02598
1 changed files with 13 additions and 0 deletions
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13
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -615,6 +615,19 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
std::swap(N1, N2);
}
}
switch (Opcode) {
default: break;
case ISD::SHL: // shl 0, X -> 0
if (N1C->isNullValue()) return N1;
break;
case ISD::SRL: // srl 0, X -> 0
if (N1C->isNullValue()) return N1;
break;
case ISD::SRA: // sra -1, X -> -1
if (N1C->isAllOnesValue()) return N1;
break;
}
}
if (N2C) {