[IR] De-virtualize ~Value to save a vptr

Summary:
Implements PR889

Removing the virtual table pointer from Value saves 1% of RSS when doing
LTO of llc on Linux. The impact on time was positive, but too noisy to
conclusively say that performance improved. Here is a link to the
spreadsheet with the original data:

https://docs.google.com/spreadsheets/d/1F4FHir0qYnV0MEp2sYYp_BuvnJgWlWPhWOwZ6LbW7W4/edit?usp=sharing

This change makes it invalid to directly delete a Value, User, or
Instruction pointer. Instead, such code can be rewritten to a null check
and a call Value::deleteValue(). Value objects tend to have their
lifetimes managed through iplist, so for the most part, this isn't a big
deal.  However, there are some places where LLVM deletes values, and
those places had to be migrated to deleteValue.  I have also created
llvm::unique_value, which has a custom deleter, so it can be used in
place of std::unique_ptr<Value>.

I had to add the "DerivedUser" Deleter escape hatch for MemorySSA, which
derives from User outside of lib/IR. Code in IR cannot include MemorySSA
headers or call the MemoryAccess object destructors without introducing
a circular dependency, so we need some level of indirection.
Unfortunately, no class derived from User may have any virtual methods,
because adding a virtual method would break User::getHungOffOperands(),
which assumes that it can find the use list immediately prior to the
User object. I've added a static_assert to the appropriate OperandTraits
templates to help people avoid this trap.

Reviewers: chandlerc, mehdi_amini, pete, dberlin, george.burgess.iv

Reviewed By: chandlerc

Subscribers: krytarowski, eraman, george.burgess.iv, mzolotukhin, Prazek, nlewycky, hans, inglorion, pcc, tejohnson, dberlin, llvm-commits

Differential Revision: https://reviews.llvm.org/D31261

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303362 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 0 insertions, 20 deletions

diff --git a/lib/IR/ConstantsContext.h b/lib/IR/ConstantsContext.h
index 25eb9452d9d..6c189cf656d 100644
--- a/lib/IR/ConstantsContext.h
+++ b/lib/IR/ConstantsContext.h
@@ -44,8 +44,6 @@ namespace llvm {
 /// UnaryConstantExpr - This class is private to Constants.cpp, and is used
 /// behind the scenes to implement unary constant exprs.
 class UnaryConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   UnaryConstantExpr(unsigned Opcode, Constant *C, Type *Ty)
     : ConstantExpr(Ty, Opcode, &Op<0>(), 1) {
@@ -65,8 +63,6 @@ public:
 /// BinaryConstantExpr - This class is private to Constants.cpp, and is used
 /// behind the scenes to implement binary constant exprs.
 class BinaryConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   BinaryConstantExpr(unsigned Opcode, Constant *C1, Constant *C2,
                      unsigned Flags)
@@ -90,8 +86,6 @@ public:
 /// SelectConstantExpr - This class is private to Constants.cpp, and is used
 /// behind the scenes to implement select constant exprs.
 class SelectConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   SelectConstantExpr(Constant *C1, Constant *C2, Constant *C3)
     : ConstantExpr(C2->getType(), Instruction::Select, &Op<0>(), 3) {
@@ -115,8 +109,6 @@ public:
 /// Constants.cpp, and is used behind the scenes to implement
 /// extractelement constant exprs.
 class ExtractElementConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   ExtractElementConstantExpr(Constant *C1, Constant *C2)
     : ConstantExpr(cast<VectorType>(C1->getType())->getElementType(),
@@ -140,8 +132,6 @@ public:
 /// Constants.cpp, and is used behind the scenes to implement
 /// insertelement constant exprs.
 class InsertElementConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   InsertElementConstantExpr(Constant *C1, Constant *C2, Constant *C3)
     : ConstantExpr(C1->getType(), Instruction::InsertElement,
@@ -166,8 +156,6 @@ public:
 /// Constants.cpp, and is used behind the scenes to implement
 /// shufflevector constant exprs.
 class ShuffleVectorConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   ShuffleVectorConstantExpr(Constant *C1, Constant *C2, Constant *C3)
   : ConstantExpr(VectorType::get(
@@ -195,8 +183,6 @@ public:
 /// Constants.cpp, and is used behind the scenes to implement
 /// extractvalue constant exprs.
 class ExtractValueConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   ExtractValueConstantExpr(Constant *Agg, ArrayRef<unsigned> IdxList,
                            Type *DestTy)
@@ -230,8 +216,6 @@ public:
 /// Constants.cpp, and is used behind the scenes to implement
 /// insertvalue constant exprs.
 class InsertValueConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   InsertValueConstantExpr(Constant *Agg, Constant *Val,
                           ArrayRef<unsigned> IdxList, Type *DestTy)
@@ -271,8 +255,6 @@ class GetElementPtrConstantExpr : public ConstantExpr {
   GetElementPtrConstantExpr(Type *SrcElementTy, Constant *C,
                             ArrayRef<Constant *> IdxList, Type *DestTy);
 
-  void anchor() override;
-
 public:
   static GetElementPtrConstantExpr *Create(Type *SrcElementTy, Constant *C,
                                            ArrayRef<Constant *> IdxList,
@@ -301,8 +283,6 @@ public:
 // behind the scenes to implement ICmp and FCmp constant expressions. This is
 // needed in order to store the predicate value for these instructions.
 class CompareConstantExpr : public ConstantExpr {
-  void anchor() override;
-
 public:
   unsigned short predicate;
   CompareConstantExpr(Type *ty, Instruction::OtherOps opc,