[DAGCombiner] Add special case fast paths for udiv x,1 and udiv x,-1

udiv x,-1 was going down the (slow) BuildUDIV route resulting in unnecessary shifts.

llvm-svn: 336701

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 7c668a1f931..20ea66d8dcc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3149,6 +3149,7 @@ SDValue DAGCombiner::visitUDIV(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   EVT VT = N->getValueType(0);
+  EVT CCVT = getSetCCResultType(VT);
 
   // fold vector ops
   if (VT.isVector())
@@ -3164,6 +3165,14 @@ SDValue DAGCombiner::visitUDIV(SDNode *N) {
     if (SDValue Folded = DAG.FoldConstantArithmetic(ISD::UDIV, DL, VT,
                                                     N0C, N1C))
       return Folded;
+  // fold (udiv X, 1) -> X
+  if (N1C && N1C->isOne())
+    return N0;
+  // fold (udiv X, -1) -> select(X == -1, 1, 0)
+  if (N1C && N1C->getAPIntValue().isAllOnesValue())
+    return DAG.getSelect(DL, VT, DAG.getSetCC(DL, CCVT, N0, N1, ISD::SETEQ),
+                         DAG.getConstant(1, DL, VT),
+                         DAG.getConstant(0, DL, VT));
 
   if (SDValue V = simplifyDivRem(N, DAG))
     return V;