Use ArrayRecycler for MachineInstr operand lists.

Instead of an std::vector<MachineOperand>, use MachineOperand arrays
from an ArrayRecycler living in MachineFunction.

This has several advantages:

- MachineInstr now has a trivial destructor, making it possible to
  delete them in batches when destroying MachineFunction. This will be
  enabled in a later patch.

- Bypassing malloc() and free() can be faster, depending on the system
  library.

- MachineInstr objects and their operands are allocated from the same
  BumpPtrAllocator, so they will usually be next to each other in
  memory, providing better locality of reference.

- Reduce MachineInstr footprint. A std::vector is 24 bytes, the new
  operand array representation only uses 8+4+1 bytes in MachineInstr.

- Better control over operand array reallocations. In the old
  representation, the use-def chains would be reordered whenever a
  std::vector reached its capacity. The new implementation never changes
  the use-def chain order.

Note that some decisions in the code generator depend on the use-def
chain orders, so this patch may cause different assembly to be produced
in a few cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171598 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineFunction.cpp

@@ -78,6 +78,7 @@ MachineFunction::MachineFunction(const Function *F, const TargetMachine &TM,
 MachineFunction::~MachineFunction() {
   BasicBlocks.clear();
   InstructionRecycler.clear(Allocator);
+  OperandRecycler.clear(Allocator);
   BasicBlockRecycler.clear(Allocator);
   if (RegInfo) {
     RegInfo->~MachineRegisterInfo();
@@ -177,6 +178,12 @@ MachineFunction::CloneMachineInstr(const MachineInstr *Orig) {
 ///
 void
 MachineFunction::DeleteMachineInstr(MachineInstr *MI) {
+  // Strip it for parts. The operand array and the MI object itself are
+  // independently recyclable.
+  if (MI->Operands)
+    deallocateOperandArray(MI->CapOperands, MI->Operands);
+  MI->Operands = 0;
+  MI->NumOperands = 0;
   MI->~MachineInstr();
   InstructionRecycler.Deallocate(Allocator, MI);
 }