[TargetLowering] fix formatting and comments for ShrinkDemandedConstant; NFC

llvm-svn: 294325

1 files changed, 20 insertions, 19 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index b37025882d9..144165ab63a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -334,34 +334,35 @@ TargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
 //  Optimization Methods
 //===----------------------------------------------------------------------===//
 
-/// Check to see if the specified operand of the specified instruction is a
-/// constant integer. If so, check to see if there are any bits set in the
-/// constant that are not demanded. If so, shrink the constant and return true.
-bool TargetLowering::TargetLoweringOpt::ShrinkDemandedConstant(SDValue Op,
-                                                        const APInt &Demanded) {
-  SDLoc dl(Op);
+/// If the specified instruction has a constant integer operand and there are
+/// bits set in that constant that are not demanded, then clear those bits and
+/// return true.
+bool TargetLowering::TargetLoweringOpt::ShrinkDemandedConstant(
+    SDValue Op, const APInt &Demanded) {
+  SDLoc DL(Op);
+  unsigned Opcode = Op.getOpcode();
 
   // FIXME: ISD::SELECT, ISD::SELECT_CC
-  switch (Op.getOpcode()) {
-  default: break;
+  switch (Opcode) {
+  default:
+    break;
   case ISD::XOR:
   case ISD::AND:
   case ISD::OR: {
-    ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1));
-    if (!C) return false;
+    auto *Op1C = dyn_cast<ConstantSDNode>(Op.getOperand(1));
+    if (!Op1C)
+      return false;
 
-    if (Op.getOpcode() == ISD::XOR &&
-        (C->getAPIntValue() | (~Demanded)).isAllOnesValue())
+    // If this is a 'not' op, don't touch it because that's a canonical form.
+    const APInt &C = Op1C->getAPIntValue();
+    if (Opcode == ISD::XOR && (C | ~Demanded).isAllOnesValue())
       return false;
 
-    // if we can expand it to have all bits set, do it
-    if (C->getAPIntValue().intersects(~Demanded)) {
+    if (C.intersects(~Demanded)) {
       EVT VT = Op.getValueType();
-      SDValue New = DAG.getNode(Op.getOpcode(), dl, VT, Op.getOperand(0),
-                                DAG.getConstant(Demanded &
-                                                C->getAPIntValue(),
-                                                dl, VT));
-      return CombineTo(Op, New);
+      SDValue NewC = DAG.getConstant(Demanded & C, DL, VT);
+      SDValue NewOp = DAG.getNode(Opcode, DL, VT, Op.getOperand(0), NewC);
+      return CombineTo(Op, NewOp);
     }
 
     break;