Add a select_cc optimization for recognizing abs(int). This speeds up an
integer MPEG encoding loop by a factor of two.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22758 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index e331c4a..12482ef 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1495,6 +1495,22 @@
return getNode(ISD::AND, AType, Shift, N3);
}
}
+
+ // Check to see if this is an integer abs. select_cc setl[te] X, 0, -X, X ->
+ // Y = sra (X, size(X)-1); xor (add (X, Y), Y)
+ if (N2C && N2C->isNullValue() && (CC == ISD::SETLT || CC == ISD::SETLE) &&
+ N1 == N4 && N3.getOpcode() == ISD::SUB && N1 == N3.getOperand(1)) {
+ if (ConstantSDNode *SubC = dyn_cast<ConstantSDNode>(N3.getOperand(0))) {
+ MVT::ValueType XType = N1.getValueType();
+ if (SubC->isNullValue() && MVT::isInteger(XType)) {
+ SDOperand Shift = getNode(ISD::SRA, XType, N1,
+ getConstant(MVT::getSizeInBits(XType)-1,
+ TLI.getShiftAmountTy()));
+ return getNode(ISD::XOR, XType, getNode(ISD::ADD, XType, N1, Shift),
+ Shift);
+ }
+ }
+ }
}
std::vector<SDOperand> Ops;