Teach DAGCombiner how to fold a SIGN_EXTEND_INREG of a BUILD_VECTOR of
ConstantSDNodes (or UNDEFs) into a simple BUILD_VECTOR.
For example, given the following sequence of dag nodes:
i32 C = Constant<1>
v4i32 V = BUILD_VECTOR C, C, C, C
v4i32 Result = SIGN_EXTEND_INREG V, ValueType:v4i1
The SIGN_EXTEND_INREG node can be folded into a build_vector since
the vector in input is a BUILD_VECTOR of constants.
The optimized sequence is:
i32 C = Constant<-1>
v4i32 Result = BUILD_VECTOR C, C, C, C
llvm-svn: 198084
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index f8728b6..68d0521 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5511,6 +5511,29 @@
BSwap, N1);
}
+ // Fold a sext_inreg of a build_vector of ConstantSDNodes or undefs
+ // into a build_vector.
+ if (ISD::isBuildVectorOfConstantSDNodes(N0.getNode())) {
+ SmallVector<SDValue, 8> Elts;
+ unsigned NumElts = N0->getNumOperands();
+ unsigned ShAmt = VTBits - EVTBits;
+
+ for (unsigned i = 0; i != NumElts; ++i) {
+ SDValue Op = N0->getOperand(i);
+ if (Op->getOpcode() == ISD::UNDEF) {
+ Elts.push_back(Op);
+ continue;
+ }
+
+ ConstantSDNode *CurrentND = cast<ConstantSDNode>(Op);
+ const APInt &C = CurrentND->getAPIntValue();
+ Elts.push_back(DAG.getConstant(C.shl(ShAmt).ashr(ShAmt),
+ Op.getValueType()));
+ }
+
+ return DAG.getNode(ISD::BUILD_VECTOR, SDLoc(N), VT, &Elts[0], NumElts);
+ }
+
return SDValue();
}