[libcxx-commits] [PATCH] D81288: [Opt] Smart pointer lifetime optimizations pass.

[Zoe Carver via Phabricator via libcxx-commits]

zoecarver created this revision.
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================
Comment at: libcxx/include/memory:2412
   _LIBCPP_INLINE_VISIBILITY
+  __attribute__((abi_tag("__SEMANTICS_unique_ptr_move_const")))
   unique_ptr(unique_ptr&& __u) _NOEXCEPT
----------------
Obviously these won't be part of the final patch. This is just an easy way to figure out which methods are important (both for me and the pass). 

In Swift, there's a `@_semantics` decorator that can be applied to functions so the compiler can apply specific optimizations. Is there anything like that in clang? If not, would something like that be welcome and/or possible? If so, I'm happy to implement it. 


This pass does one thing: constant fold away the destructor of `unique_ptr` based on ownership information we get form move semantics.

However, it is also (hopefully) the scaffolding for many more lifetime optimizations both around `unique_ptr` and other smart pointers.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D81288

Files:
  libcxx/include/memory
  llvm/include/llvm/InitializePasses.h
  llvm/include/llvm/LinkAllPasses.h
  llvm/include/llvm/Transforms/Scalar.h
  llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
  llvm/lib/Transforms/Scalar/CMakeLists.txt
  llvm/lib/Transforms/Scalar/Scalar.cpp
  llvm/lib/Transforms/Scalar/SmartPtrLifetime.cpp
  llvm/test/Transforms/SmartPtrLifetime/simple.ll

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