From 96ab8726a3c2676c614b4d38500478046f816ce2 Mon Sep 17 00:00:00 2001 From: Reid Kleckner Date: Thu, 18 May 2017 17:24:10 +0000 Subject: [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. 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 llvm-svn: 303362 --- llvm/lib/IR/Function.cpp | 2 -- 1 file changed, 2 deletions(-) (limited to 'llvm/lib/IR/Function.cpp') diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp index 16a9e51b830..39de4b0a97f 100644 --- a/llvm/lib/IR/Function.cpp +++ b/llvm/lib/IR/Function.cpp @@ -66,8 +66,6 @@ template class llvm::SymbolTableListTraits; // Argument Implementation //===----------------------------------------------------------------------===// -void Argument::anchor() {} - Argument::Argument(Type *Ty, const Twine &Name, Function *Par, unsigned ArgNo) : Value(Ty, Value::ArgumentVal), Parent(Par), ArgNo(ArgNo) { setName(Name); -- cgit v1.2.3