[DAGCombiner] Recognize another rotation idiom
This is the new idiom:
x<<(y&31) | x>>((0-y)&31)
which is recognized as:
x ROTL (y&31)
The change refines matchRotateSub. In
Neg & (OpSize - 1) == (OpSize - Pos) & (OpSize - 1), if Pos is
Pos' & (OpSize - 1) we can just use Pos' instead of Pos.
llvm-svn: 203315
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 97885d4..f938818 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3466,6 +3466,14 @@
return 0;
SDValue NegOp1 = Neg.getOperand(1);
+ // On the RHS of [A], if Pos is Pos' & (OpSize - 1), just replace Pos with
+ // Pos'. The truncation is redundant for the purpose of the equality.
+ if (MaskLoBits &&
+ Pos.getOpcode() == ISD::AND &&
+ Pos.getOperand(1).getOpcode() == ISD::Constant &&
+ cast<ConstantSDNode>(Pos.getOperand(1))->getAPIntValue() == OpSize - 1)
+ Pos = Pos.getOperand(0);
+
// The condition we need is now:
//
// (NegC - NegOp1) & Mask == (OpSize - Pos) & Mask