[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

llvm-svn: 339740

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp b/llvm/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp
index 005f5f44a63..b196c013902 100644
--- a/llvm/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp
@@ -362,12 +362,11 @@ bool MSP430DAGToDAGISel::tryIndexedBinOp(SDNode *Op, SDValue N1, SDValue N2,
 
     MVT VT = LD->getMemoryVT().getSimpleVT();
     unsigned Opc = (VT == MVT::i16 ? Opc16 : Opc8);
-    MachineSDNode::mmo_iterator MemRefs0 = MF->allocateMemRefsArray(1);
-    MemRefs0[0] = cast<MemSDNode>(N1)->getMemOperand();
+    MachineMemOperand *MemRef = cast<MemSDNode>(N1)->getMemOperand();
     SDValue Ops0[] = { N2, LD->getBasePtr(), LD->getChain() };
     SDNode *ResNode =
       CurDAG->SelectNodeTo(Op, Opc, VT, MVT::i16, MVT::Other, Ops0);
-    cast<MachineSDNode>(ResNode)->setMemRefs(MemRefs0, MemRefs0 + 1);
+    CurDAG->setNodeMemRefs(cast<MachineSDNode>(ResNode), {MemRef});
     // Transfer chain.
     ReplaceUses(SDValue(N1.getNode(), 2), SDValue(ResNode, 2));
     // Transfer writeback.