fold (sra (sra x, c1), c2) -> (sra x, c1+c2)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26416 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b9c560d..da63be3 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -23,9 +23,6 @@
// FIXME: mul (x, const) -> shifts + adds
// FIXME: undef values
// FIXME: make truncate see through SIGN_EXTEND and AND
-// FIXME: (sra (sra x, c1), c2) -> (sra x, c1+c2)
-// FIXME: verify that getNode can't return extends with an operand whose type
-// is >= to that of the extend.
// FIXME: divide by zero is currently left unfolded. do we want to turn this
// into an undef?
// FIXME: select ne (select cc, 1, 0), 0, true, false -> select cc, true, false
@@ -1367,6 +1364,17 @@
return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0.getOperand(0),
DAG.getValueType(EVT));
}
+
+ // fold (sra (sra x, c1), c2) -> (sra x, c1+c2)
+ if (N1C && N0.getOpcode() == ISD::SRA) {
+ if (ConstantSDNode *C1 = dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
+ unsigned Sum = N1C->getValue() + C1->getValue();
+ if (Sum >= MVT::getSizeInBits(VT)) Sum = MVT::getSizeInBits(VT)-1;
+ return DAG.getNode(ISD::SRA, VT, N0.getOperand(0),
+ DAG.getConstant(Sum, N1C->getValueType(0)));
+ }
+ }
+
// If the sign bit is known to be zero, switch this to a SRL.
if (TLI.MaskedValueIsZero(N0, MVT::getIntVTSignBit(VT)))
return DAG.getNode(ISD::SRL, VT, N0, N1);