From 2c2e76a9e24a9f90808dfa159af05712bf9236e7 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Fri, 8 Mar 2019 11:16:55 +0000
Subject: [PATCH] [DAGCombine] Merge visitSSUBO+visitUSUBO into visitSUBO.
 NFCI.

llvm-svn: 355688
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 41 ++++++---------------------
 1 file changed, 8 insertions(+), 33 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 770c15c..9371161 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -299,8 +299,7 @@ namespace {
     SDValue visitUADDO(SDNode *N);
     SDValue visitUADDOLike(SDValue N0, SDValue N1, SDNode *N);
     SDValue visitSUBC(SDNode *N);
-    SDValue visitSSUBO(SDNode *N);
-    SDValue visitUSUBO(SDNode *N);
+    SDValue visitSUBO(SDNode *N);
     SDValue visitADDE(SDNode *N);
     SDValue visitADDCARRY(SDNode *N);
     SDValue visitADDCARRYLike(SDValue N0, SDValue N1, SDValue CarryIn, SDNode *N);
@@ -1497,8 +1496,8 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::SADDO:              return visitSADDO(N);
   case ISD::UADDO:              return visitUADDO(N);
   case ISD::SUBC:               return visitSUBC(N);
-  case ISD::SSUBO:              return visitSSUBO(N);
-  case ISD::USUBO:              return visitUSUBO(N);
+  case ISD::SSUBO:
+  case ISD::USUBO:              return visitSUBO(N);
   case ISD::ADDE:               return visitADDE(N);
   case ISD::ADDCARRY:           return visitADDCARRY(N);
   case ISD::SUBE:               return visitSUBE(N);
@@ -2925,35 +2924,11 @@ SDValue DAGCombiner::visitSUBC(SDNode *N) {
   return SDValue();
 }
 
-// TODO: merge this with DAGCombiner::visitUSUBO
-SDValue DAGCombiner::visitSSUBO(SDNode *N) {
-  SDValue N0 = N->getOperand(0);
-  SDValue N1 = N->getOperand(1);
-  EVT VT = N0.getValueType();
-  EVT CarryVT = N->getValueType(1);
-  SDLoc DL(N);
-
-  // If the flag result is dead, turn this into an SUB.
-  if (!N->hasAnyUseOfValue(1))
-    return CombineTo(N, DAG.getNode(ISD::SUB, DL, VT, N0, N1),
-                     DAG.getUNDEF(CarryVT));
-
-  // fold (ssubo x, x) -> 0 + no borrow
-  if (N0 == N1)
-    return CombineTo(N, DAG.getConstant(0, DL, VT),
-                     DAG.getConstant(0, DL, CarryVT));
-
-  // fold (ssubo x, 0) -> x + no borrow
-  if (isNullOrNullSplat(N1))
-    return CombineTo(N, N0, DAG.getConstant(0, DL, CarryVT));
-
-  return SDValue();
-}
-
-SDValue DAGCombiner::visitUSUBO(SDNode *N) {
+SDValue DAGCombiner::visitSUBO(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   EVT VT = N0.getValueType();
+  bool IsSigned = (ISD::SSUBO == N->getOpcode());
 
   EVT CarryVT = N->getValueType(1);
   SDLoc DL(N);
@@ -2963,17 +2938,17 @@ SDValue DAGCombiner::visitUSUBO(SDNode *N) {
     return CombineTo(N, DAG.getNode(ISD::SUB, DL, VT, N0, N1),
                      DAG.getUNDEF(CarryVT));
 
-  // fold (usubo x, x) -> 0 + no borrow
+  // fold (subo x, x) -> 0 + no borrow
   if (N0 == N1)
     return CombineTo(N, DAG.getConstant(0, DL, VT),
                      DAG.getConstant(0, DL, CarryVT));
 
-  // fold (usubo x, 0) -> x + no borrow
+  // fold (subo x, 0) -> x + no borrow
   if (isNullOrNullSplat(N1))
     return CombineTo(N, N0, DAG.getConstant(0, DL, CarryVT));
 
   // Canonicalize (usubo -1, x) -> ~x, i.e. (xor x, -1) + no borrow
-  if (isAllOnesOrAllOnesSplat(N0))
+  if (!IsSigned && isAllOnesOrAllOnesSplat(N0))
     return CombineTo(N, DAG.getNode(ISD::XOR, DL, VT, N1, N0),
                      DAG.getConstant(0, DL, CarryVT));
 
-- 
2.7.4