[DAG] add helper to bind memop chains; NFCI

This step is just intended to reduce code duplication rather than change any functionality.

A follow-up would be to replace PPCTargetLowering::spliceIntoChain() usage with this new helper.

Differential Revision: https://reviews.llvm.org/D33649

llvm-svn: 305192

llvm/include/llvm/CodeGen/SelectionDAG.h

@@ -1217,6 +1217,12 @@ class SelectionDAG {
   void ReplaceAllUsesOfValuesWith(const SDValue *From, const SDValue *To,
                                   unsigned Num);
 
+  /// If an existing load has uses of its chain, create a token factor node with
+  /// that chain and the new memory node's chain and update users of the old
+  /// chain to the token factor. This ensures that the new memory node will have
+  /// the same relative memory dependency position as the old load.
+  void makeEquivalentMemoryOrdering(LoadSDNode *Old, SDValue New);
+
   /// Topological-sort the AllNodes list and a
   /// assign a unique node id for each node in the DAG based on their
   /// topological order. Returns the number of nodes.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -14693,21 +14693,7 @@ static SDValue narrowExtractedVectorLoad(SDNode *Extract, SelectionDAG &DAG) {
   MachineMemOperand *MMO = MF.getMachineMemOperand(Ld->getMemOperand(), Offset,
                                                    VT.getStoreSize());
   SDValue NewLd = DAG.getLoad(VT, DL, Ld->getChain(), NewAddr, MMO);
-
-  // The new load must have the same position as the old load in terms of memory
-  // dependency. Create a TokenFactor for Ld and NewLd and update uses of Ld's
-  // output chain to use that TokenFactor.
-  // TODO: This code is based on a similar sequence in x86 lowering. It should
-  // be moved to a helper function, so it can be shared and reused.
-  if (Ld->hasAnyUseOfValue(1)) {
-    SDValue OldChain = SDValue(Ld, 1);
-    SDValue NewChain = SDValue(NewLd.getNode(), 1);
-    SDValue TokenFactor = DAG.getNode(ISD::TokenFactor, DL, MVT::Other,
-                                      OldChain, NewChain);
-    DAG.ReplaceAllUsesOfValueWith(OldChain, TokenFactor);
-    DAG.UpdateNodeOperands(TokenFactor.getNode(), OldChain, NewChain);
-  }
-
+  DAG.makeEquivalentMemoryOrdering(Ld, NewLd);
   return NewLd;
 }
 

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -7244,6 +7244,24 @@ void SelectionDAG::TransferDbgValues(SDValue From, SDValue To) {
     AddDbgValue(I, ToNode, false);
 }
 
+void SelectionDAG::makeEquivalentMemoryOrdering(LoadSDNode *OldLoad,
+                                                SDValue NewMemOp) {
+  assert(isa<MemSDNode>(NewMemOp.getNode()) && "Expected a memop node");
+  if (!OldLoad->hasAnyUseOfValue(1))
+    return;
+
+  // The new memory operation must have the same position as the old load in
+  // terms of memory dependency. Create a TokenFactor for the old load and new
+  // memory operation and update uses of the old load's output chain to use that
+  // TokenFactor.
+  SDValue OldChain = SDValue(OldLoad, 1);
+  SDValue NewChain = SDValue(NewMemOp.getNode(), 1);
+  SDValue TokenFactor =
+      getNode(ISD::TokenFactor, SDLoc(OldLoad), MVT::Other, OldChain, NewChain);
+  ReplaceAllUsesOfValueWith(OldChain, TokenFactor);
+  UpdateNodeOperands(TokenFactor.getNode(), OldChain, NewChain);
+}
+
 //===----------------------------------------------------------------------===//
 //                              SDNode Class
 //===----------------------------------------------------------------------===//

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -6819,6 +6819,7 @@ bool PPCTargetLowering::canReuseLoadAddress(SDValue Op, EVT MemVT,
 // Given the head of the old chain, ResChain, insert a token factor containing
 // it and NewResChain, and make users of ResChain now be users of that token
 // factor.
+// TODO: Remove and use DAG::makeEquivalentMemoryOrdering() instead.
 void PPCTargetLowering::spliceIntoChain(SDValue ResChain,
                                         SDValue NewResChain,
                                         SelectionDAG &DAG) const {

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -6491,16 +6491,7 @@ static SDValue EltsFromConsecutiveLoads(EVT VT, ArrayRef<SDValue> Elts,
     SDValue NewLd =
         DAG.getLoad(VT, DL, LDBase->getChain(), LDBase->getBasePtr(),
                     LDBase->getPointerInfo(), LDBase->getAlignment(), MMOFlags);
-
-    if (LDBase->hasAnyUseOfValue(1)) {
-      SDValue NewChain =
-          DAG.getNode(ISD::TokenFactor, DL, MVT::Other, SDValue(LDBase, 1),
-                      SDValue(NewLd.getNode(), 1));
-      DAG.ReplaceAllUsesOfValueWith(SDValue(LDBase, 1), NewChain);
-      DAG.UpdateNodeOperands(NewChain.getNode(), SDValue(LDBase, 1),
-                             SDValue(NewLd.getNode(), 1));
-    }
-
+    DAG.makeEquivalentMemoryOrdering(LDBase, NewLd);
     return NewLd;
   };
 
@@ -6565,19 +6556,7 @@ static SDValue EltsFromConsecutiveLoads(EVT VT, ArrayRef<SDValue> Elts,
                                   LDBase->getAlignment(),
                                   false/*isVolatile*/, true/*ReadMem*/,
                                   false/*WriteMem*/);
-
-      // Make sure the newly-created LOAD is in the same position as LDBase in
-      // terms of dependency. We create a TokenFactor for LDBase and ResNode,
-      // and update uses of LDBase's output chain to use the TokenFactor.
-      if (LDBase->hasAnyUseOfValue(1)) {
-        SDValue NewChain =
-            DAG.getNode(ISD::TokenFactor, DL, MVT::Other, SDValue(LDBase, 1),
-                        SDValue(ResNode.getNode(), 1));
-        DAG.ReplaceAllUsesOfValueWith(SDValue(LDBase, 1), NewChain);
-        DAG.UpdateNodeOperands(NewChain.getNode(), SDValue(LDBase, 1),
-                               SDValue(ResNode.getNode(), 1));
-      }
-
+      DAG.makeEquivalentMemoryOrdering(LDBase, ResNode);
       return DAG.getBitcast(VT, ResNode);
     }
   }
@@ -9930,17 +9909,7 @@ static SDValue lowerVectorShuffleAsBroadcast(const SDLoc &DL, MVT VT,
     V = DAG.getLoad(SVT, DL, Ld->getChain(), NewAddr,
                     DAG.getMachineFunction().getMachineMemOperand(
                         Ld->getMemOperand(), Offset, SVT.getStoreSize()));
-
-    // Make sure the newly-created LOAD is in the same position as Ld in
-    // terms of dependency. We create a TokenFactor for Ld and V,
-    // and update uses of Ld's output chain to use the TokenFactor.
-    if (Ld->hasAnyUseOfValue(1)) {
-      SDValue NewChain = DAG.getNode(ISD::TokenFactor, DL, MVT::Other,
-                                     SDValue(Ld, 1), SDValue(V.getNode(), 1));
-      DAG.ReplaceAllUsesOfValueWith(SDValue(Ld, 1), NewChain);
-      DAG.UpdateNodeOperands(NewChain.getNode(), SDValue(Ld, 1),
-                             SDValue(V.getNode(), 1));
-    }
+    DAG.makeEquivalentMemoryOrdering(Ld, V);
   } else if (!BroadcastFromReg) {
     // We can't broadcast from a vector register.
     return SDValue();