[SDAG] Remove the reliance on MI's allocation strategy for

`MachineMemOperand` pointers attached to `MachineSDNodes` and instead
have the `SelectionDAG` fully manage the memory for this array.

Prior to this change, the memory management was deeply confusing here --
The way the MI was built relied on the `SelectionDAG` allocating memory
for these arrays of pointers using the `MachineFunction`'s allocator so
that the raw pointer to the array could be blindly copied into an
eventual `MachineInstr`. This creates a hard coupling between how
`MachineInstr`s allocate their array of `MachineMemOperand` pointers and
how the `MachineSDNode` does.

This change is motivated in large part by a change I am making to how
`MachineFunction` allocates these pointers, but it seems like a layering
improvement as well.

This would run the risk of increasing allocations overall, but I've
implemented an optimization that should avoid that by storing a single
`MachineMemOperand` pointer directly instead of allocating anything.
This is expected to be a net win because the vast majority of uses of
these only need a single pointer.

As a side-effect, this makes the API for updating a `MachineSDNode` and
a `MachineInstr` reasonably different which seems nice to avoid
unexpected coupling of these two layers. We can map between them, but we
shouldn't be *surprised* at where that occurs. =]

Differential Revision: https://reviews.llvm.org/D50680

1 files changed, 14 insertions, 21 deletions

diff --git a/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp b/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp
index 21939d836dc..ffc6a59cd6c 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp
@@ -981,9 +981,8 @@ bool NVPTXDAGToDAGISel::tryLoad(SDNode *N) {
   if (!NVPTXLD)
     return false;
 
-  MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-  MemRefs0[0] = cast<MemSDNode>(N)->getMemOperand();
-  cast<MachineSDNode>(NVPTXLD)->setMemRefs(MemRefs0, MemRefs0 + 1);
+  MachineMemOperand *MemRef = cast<MemSDNode>(N)->getMemOperand();
+  CurDAG->setNodeMemRefs(cast<MachineSDNode>(NVPTXLD), {MemRef});
 
   ReplaceNode(N, NVPTXLD);
   return true;
@@ -1221,9 +1220,8 @@ bool NVPTXDAGToDAGISel::tryLoadVector(SDNode *N) {
     LD = CurDAG->getMachineNode(Opcode.getValue(), DL, N->getVTList(), Ops);
   }
 
-  MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-  MemRefs0[0] = cast<MemSDNode>(N)->getMemOperand();
-  cast<MachineSDNode>(LD)->setMemRefs(MemRefs0, MemRefs0 + 1);
+  MachineMemOperand *MemRef = cast<MemSDNode>(N)->getMemOperand();
+  CurDAG->setNodeMemRefs(cast<MachineSDNode>(LD), {MemRef});
 
   ReplaceNode(N, LD);
   return true;
@@ -1659,9 +1657,8 @@ bool NVPTXDAGToDAGISel::tryLDGLDU(SDNode *N) {
     LD = CurDAG->getMachineNode(Opcode.getValue(), DL, InstVTList, Ops);
   }
 
-  MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-  MemRefs0[0] = Mem->getMemOperand();
-  cast<MachineSDNode>(LD)->setMemRefs(MemRefs0, MemRefs0 + 1);
+  MachineMemOperand *MemRef = Mem->getMemOperand();
+  CurDAG->setNodeMemRefs(cast<MachineSDNode>(LD), {MemRef});
 
   // For automatic generation of LDG (through SelectLoad[Vector], not the
   // intrinsics), we may have an extending load like:
@@ -1864,9 +1861,8 @@ bool NVPTXDAGToDAGISel::tryStore(SDNode *N) {
   if (!NVPTXST)
     return false;
 
-  MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-  MemRefs0[0] = cast<MemSDNode>(N)->getMemOperand();
-  cast<MachineSDNode>(NVPTXST)->setMemRefs(MemRefs0, MemRefs0 + 1);
+  MachineMemOperand *MemRef = cast<MemSDNode>(N)->getMemOperand();
+  CurDAG->setNodeMemRefs(cast<MachineSDNode>(NVPTXST), {MemRef});
   ReplaceNode(N, NVPTXST);
   return true;
 }
@@ -2088,9 +2084,8 @@ bool NVPTXDAGToDAGISel::tryStoreVector(SDNode *N) {
 
   ST = CurDAG->getMachineNode(Opcode.getValue(), DL, MVT::Other, StOps);
 
-  MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-  MemRefs0[0] = cast<MemSDNode>(N)->getMemOperand();
-  cast<MachineSDNode>(ST)->setMemRefs(MemRefs0, MemRefs0 + 1);
+  MachineMemOperand *MemRef = cast<MemSDNode>(N)->getMemOperand();
+  CurDAG->setNodeMemRefs(cast<MachineSDNode>(ST), {MemRef});
 
   ReplaceNode(N, ST);
   return true;
@@ -2236,9 +2231,8 @@ bool NVPTXDAGToDAGISel::tryStoreRetval(SDNode *N) {
     return false;
 
   SDNode *Ret = CurDAG->getMachineNode(Opcode.getValue(), DL, MVT::Other, Ops);
-  MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-  MemRefs0[0] = cast<MemSDNode>(N)->getMemOperand();
-  cast<MachineSDNode>(Ret)->setMemRefs(MemRefs0, MemRefs0 + 1);
+  MachineMemOperand *MemRef = cast<MemSDNode>(N)->getMemOperand();
+  CurDAG->setNodeMemRefs(cast<MachineSDNode>(Ret), {MemRef});
 
   ReplaceNode(N, Ret);
   return true;
@@ -2341,9 +2335,8 @@ bool NVPTXDAGToDAGISel::tryStoreParam(SDNode *N) {
   SDVTList RetVTs = CurDAG->getVTList(MVT::Other, MVT::Glue);
   SDNode *Ret =
       CurDAG->getMachineNode(Opcode.getValue(), DL, RetVTs, Ops);
-  MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-  MemRefs0[0] = cast<MemSDNode>(N)->getMemOperand();
-  cast<MachineSDNode>(Ret)->setMemRefs(MemRefs0, MemRefs0 + 1);
+  MachineMemOperand *MemRef = cast<MemSDNode>(N)->getMemOperand();
+  CurDAG->setNodeMemRefs(cast<MachineSDNode>(Ret), {MemRef});
 
   ReplaceNode(N, Ret);
   return true;