[DAGCombiner] Some very basic add/sub saturation combines.

Handle combines with zero and constant canonicalization for adds.

llvm-svn: 351024

1 files changed, 64 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 12b03f3c6c3..104b8d00a86 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -293,6 +293,8 @@ namespace {
     SDValue visitADD(SDNode *N);
     SDValue visitADDLike(SDValue N0, SDValue N1, SDNode *LocReference);
     SDValue visitSUB(SDNode *N);
+    SDValue visitADDSAT(SDNode *N);
+    SDValue visitSUBSAT(SDNode *N);
     SDValue visitADDC(SDNode *N);
     SDValue visitUADDO(SDNode *N);
     SDValue visitUADDOLike(SDValue N0, SDValue N1, SDNode *N);
@@ -1486,6 +1488,10 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::MERGE_VALUES:       return visitMERGE_VALUES(N);
   case ISD::ADD:                return visitADD(N);
   case ISD::SUB:                return visitSUB(N);
+  case ISD::SADDSAT:
+  case ISD::UADDSAT:            return visitADDSAT(N);
+  case ISD::SSUBSAT:
+  case ISD::USUBSAT:            return visitSUBSAT(N);
   case ISD::ADDC:               return visitADDC(N);
   case ISD::UADDO:              return visitUADDO(N);
   case ISD::SUBC:               return visitSUBC(N);
@@ -2170,6 +2176,39 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitADDSAT(SDNode *N) {
+  unsigned Opcode = N->getOpcode();
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  EVT VT = N0.getValueType();
+  SDLoc DL(N);
+
+  // fold vector ops
+  if (VT.isVector()) {
+    // TODO SimplifyVBinOp
+
+    // fold (add_sat x, 0) -> x, vector edition
+    if (ISD::isBuildVectorAllZeros(N1.getNode()))
+      return N0;
+    if (ISD::isBuildVectorAllZeros(N0.getNode()))
+      return N1;
+  }
+
+  if (DAG.isConstantIntBuildVectorOrConstantInt(N0)) {
+    // canonicalize constant to RHS
+    if (!DAG.isConstantIntBuildVectorOrConstantInt(N1))
+      return DAG.getNode(Opcode, DL, VT, N1, N0);
+
+    // TODO Constant Folding
+  }
+
+  // fold (add_sat x, 0) -> x
+  if (isNullConstant(N1))
+    return N0;
+
+  return SDValue();
+}
+
 static SDValue getAsCarry(const TargetLowering &TLI, SDValue V) {
   bool Masked = false;
 
@@ -2732,6 +2771,31 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitSUBSAT(SDNode *N) {
+  unsigned Opcode = N->getOpcode();
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  EVT VT = N0.getValueType();
+  SDLoc DL(N);
+
+  // fold vector ops
+  if (VT.isVector()) {
+    // TODO SimplifyVBinOp
+
+    // fold (sub_sat x, 0) -> x, vector edition
+    if (ISD::isBuildVectorAllZeros(N1.getNode()))
+      return N0;
+  }
+
+  // TODO Constant Folding
+
+  // fold (sub_sat x, 0) -> x
+  if (isNullConstant(N1))
+    return N0;
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitSUBC(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);