Do not legalize large add with addc/adde, introduce addcarry and do it with uaddo/addcarry

Summary: As per discution on how to get better codegen an large int legalization, it became clear that using a glue for the carry was preventing several desirable optimizations. Passing the carry down as a value allow for more flexibility.

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: igorb, llvm-commits

Differential Revision: https://reviews.llvm.org/D29872

llvm-svn: 301775

1 files changed, 41 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 7560027ab4b..10542dc0ca3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -240,7 +240,9 @@ namespace {
     SDValue visitSUBC(SDNode *N);
     SDValue visitUSUBO(SDNode *N);
     SDValue visitADDE(SDNode *N);
+    SDValue visitADDCARRY(SDNode *N);
     SDValue visitSUBE(SDNode *N);
+    SDValue visitSUBCARRY(SDNode *N);
     SDValue visitMUL(SDNode *N);
     SDValue useDivRem(SDNode *N);
     SDValue visitSDIV(SDNode *N);
@@ -1413,7 +1415,9 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::SUBC:               return visitSUBC(N);
   case ISD::USUBO:              return visitUSUBO(N);
   case ISD::ADDE:               return visitADDE(N);
+  case ISD::ADDCARRY:           return visitADDCARRY(N);
   case ISD::SUBE:               return visitSUBE(N);
+  case ISD::SUBCARRY:           return visitSUBCARRY(N);
   case ISD::MUL:                return visitMUL(N);
   case ISD::SDIV:               return visitSDIV(N);
   case ISD::UDIV:               return visitUDIV(N);
@@ -2095,6 +2099,25 @@ SDValue DAGCombiner::visitADDE(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitADDCARRY(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  SDValue CarryIn = N->getOperand(2);
+
+  // canonicalize constant to RHS
+  ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
+  ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
+  if (N0C && !N1C)
+    return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(),
+                       N1, N0, CarryIn);
+
+  // fold (addcarry x, y, false) -> (uaddo x, y)
+  if (isNullConstant(CarryIn))
+    return DAG.getNode(ISD::UADDO, SDLoc(N), N->getVTList(), N0, N1);
+
+  return SDValue();
+}
+
 // Since it may not be valid to emit a fold to zero for vector initializers
 // check if we can before folding.
 static SDValue tryFoldToZero(const SDLoc &DL, const TargetLowering &TLI, EVT VT,
@@ -2327,6 +2350,18 @@ SDValue DAGCombiner::visitSUBE(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitSUBCARRY(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  SDValue CarryIn = N->getOperand(2);
+
+  // fold (subcarry x, y, false) -> (usubo x, y)
+  if (isNullConstant(CarryIn))
+    return DAG.getNode(ISD::USUBO, SDLoc(N), N->getVTList(), N0, N1);
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitMUL(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
@@ -8245,15 +8280,16 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
     return SDValue(N, 0);
 
   // (trunc adde(X, Y, Carry)) -> (adde trunc(X), trunc(Y), Carry)
+  // (trunc addcarry(X, Y, Carry)) -> (addcarry trunc(X), trunc(Y), Carry)
   // When the adde's carry is not used.
-  if (N0.getOpcode() == ISD::ADDE && N0.hasOneUse() &&
-      !N0.getNode()->hasAnyUseOfValue(1) &&
-      (!LegalOperations || TLI.isOperationLegal(ISD::ADDE, VT))) {
+  if ((N0.getOpcode() == ISD::ADDE || N0.getOpcode() == ISD::ADDCARRY) &&
+      N0.hasOneUse() && !N0.getNode()->hasAnyUseOfValue(1) &&
+      (!LegalOperations || TLI.isOperationLegal(N0.getOpcode(), VT))) {
     SDLoc SL(N);
     auto X = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(0));
     auto Y = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(1));
-    return DAG.getNode(ISD::ADDE, SL, DAG.getVTList(VT, MVT::Glue),
-                       X, Y, N0.getOperand(2));
+    auto VTs = DAG.getVTList(VT, N0->getValueType(1));
+    return DAG.getNode(N0.getOpcode(), SL, VTs, X, Y, N0.getOperand(2));
   }
 
   return SDValue();