Make the canonicalisation on shifts benifit to more case.

1.Fix pessimized case in FIXME.
2.Add tests for it.
3.The canonicalisation on shifts results in different sequence for
  tests of machine-licm.Correct some check lines.

Differential Revision: https://reviews.llvm.org/D27916

llvm-svn: 290410

1 files changed, 13 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 1d28124ce7a..b4b41c3d001 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4544,16 +4544,20 @@ SDValue DAGCombiner::visitShiftByConstant(SDNode *N, ConstantSDNode *Amt) {
   ConstantSDNode *BinOpCst = getAsNonOpaqueConstant(LHS->getOperand(1));
   if (!BinOpCst) return SDValue();
 
-  // FIXME: disable this unless the input to the binop is a shift by a constant.
-  // If it is not a shift, it pessimizes some common cases like:
-  //
-  //    void foo(int *X, int i) { X[i & 1235] = 1; }
-  //    int bar(int *X, int i) { return X[i & 255]; }
+  // FIXME: disable this unless the input to the binop is a shift by a constant
+  // or is copy/select.Enable this in other cases when figure out it's exactly profitable.
   SDNode *BinOpLHSVal = LHS->getOperand(0).getNode();
-  if ((BinOpLHSVal->getOpcode() != ISD::SHL &&
-       BinOpLHSVal->getOpcode() != ISD::SRA &&
-       BinOpLHSVal->getOpcode() != ISD::SRL) ||
-      !isa<ConstantSDNode>(BinOpLHSVal->getOperand(1)))
+  bool isShift = BinOpLHSVal->getOpcode() == ISD::SHL ||
+                 BinOpLHSVal->getOpcode() == ISD::SRA ||
+                 BinOpLHSVal->getOpcode() == ISD::SRL;
+  bool isCopyOrSelect = BinOpLHSVal->getOpcode() == ISD::CopyFromReg ||
+                        BinOpLHSVal->getOpcode() == ISD::SELECT;
+
+  if ((!isShift || !isa<ConstantSDNode>(BinOpLHSVal->getOperand(1))) &&
+      !isCopyOrSelect)
+    return SDValue();
+
+  if (isCopyOrSelect && N->hasOneUse())
     return SDValue();
 
   EVT VT = N->getValueType(0);