[TargetLowering] add tests to show effect of setcc sub->shift; NFC

There's effectively no difference for the cases with variables.
We just trade a sub for an add on those. But the case with a
subtract from constant would require an extra move instruction
on x86, so this looks like a reasonable generic combine.

llvm-svn: 353619

1 files changed, 0 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index b933f032409..eae5a45906f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3075,7 +3075,6 @@ SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
                                 DAG.getConstant(0, dl, N0.getValueType()),
                                 Cond);
           // The shift is not valid if this is a bool (i1).
-          // TODO: This transform needs evidence to justify its existence.
           if (N0.getNode()->hasOneUse() && OpVT.getScalarSizeInBits() != 1) {
             assert(N0.getOpcode() == ISD::SUB && "Unexpected operation!");
             auto &DL = DAG.getDataLayout();