Don't call destructors on MachineInstr and MachineOperand.

The series of patches leading up to this one makes llc -O0 run 8% faster.

When deallocating a MachineFunction, there is no need to visit all
MachineInstr and MachineOperand objects to deallocate them. All their
memory come from a BumpPtrAllocator that is about to be purged, and they
have empty destructors anyway.

This only applies when deallocating the MachineFunction.
DeleteMachineInstr() should still be used to recycle MI memory during
the codegen passes.

Remove the LeakDetector support for MachineInstr. I've never seen it
used before, and now it definitely doesn't work. With this patch, leaked
MachineInstrs would be much less of a problem since all of their memory
will be reclaimed by ~MachineFunction().

llvm-svn: 171599

1 files changed, 12 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index 08d116afead..9647e83e24c 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -76,7 +76,13 @@ MachineFunction::MachineFunction(const Function *F, const TargetMachine &TM,
 }
 
 MachineFunction::~MachineFunction() {
-  BasicBlocks.clear();
+  // Don't call destructors on MachineInstr and MachineOperand. All of their
+  // memory comes from the BumpPtrAllocator which is about to be purged.
+  //
+  // Do call MachineBasicBlock destructors, it contains std::vectors.
+  for (iterator I = begin(), E = end(); I != E; I = BasicBlocks.erase(I))
+    I->Insts.clearAndLeakNodesUnsafely();
+
   InstructionRecycler.clear(Allocator);
   OperandRecycler.clear(Allocator);
   BasicBlockRecycler.clear(Allocator);
@@ -176,15 +182,17 @@ MachineFunction::CloneMachineInstr(const MachineInstr *Orig) {
 
 /// DeleteMachineInstr - Delete the given MachineInstr.
 ///
+/// This function also serves as the MachineInstr destructor - the real
+/// ~MachineInstr() destructor must be empty.
 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();
+  // Don't call ~MachineInstr() which must be trivial anyway because
+  // ~MachineFunction drops whole lists of MachineInstrs wihout calling their
+  // destructors.
   InstructionRecycler.Deallocate(Allocator, MI);
 }