[all-commits] [llvm/llvm-project] 4a64d8: [ObjC][ARC] Use operand bundle 'clang.arc.rv' inst...

[Akira Hatanaka via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4a64d8fe392449b205e59031aad5424968cf7446
      https://github.com/llvm/llvm-project/commit/4a64d8fe392449b205e59031aad5424968cf7446
  Author: Akira Hatanaka <ahatanaka at apple.com>
  Date:   2021-02-05 (Fri, 05 Feb 2021)

  Changed paths:
    M clang/lib/CodeGen/CGObjC.cpp
    M clang/lib/CodeGen/CodeGenFunction.h
    M clang/lib/CodeGen/CodeGenModule.h
    A clang/test/CodeGenObjC/arc-rv-attr.m
    M clang/test/CodeGenObjC/arc-unsafeclaim.m
    M llvm/docs/LangRef.rst
    A llvm/include/llvm/Analysis/ObjCARCUtil.h
    M llvm/include/llvm/IR/InstrTypes.h
    M llvm/include/llvm/IR/Intrinsics.td
    M llvm/include/llvm/IR/LLVMContext.h
    M llvm/lib/Analysis/ObjCARCInstKind.cpp
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    M llvm/lib/IR/Instructions.cpp
    M llvm/lib/IR/LLVMContext.cpp
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/lib/Transforms/ObjCARC/ARCRuntimeEntryPoints.h
    M llvm/lib/Transforms/ObjCARC/ObjCARC.cpp
    M llvm/lib/Transforms/ObjCARC/ObjCARC.h
    M llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp
    M llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
    M llvm/lib/Transforms/ObjCARC/PtrState.cpp
    M llvm/lib/Transforms/ObjCARC/PtrState.h
    M llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp
    M llvm/lib/Transforms/Utils/InlineFunction.cpp
    M llvm/test/Bitcode/operand-bundles-bc-analyzer.ll
    M llvm/test/CodeGen/AArch64/call-rv-marker.ll
    M llvm/test/Transforms/DeadArgElim/deadretval.ll
    A llvm/test/Transforms/Inline/inline-retainRV-call.ll
    M llvm/test/Transforms/ObjCARC/contract-marker-funclet.ll
    A llvm/test/Transforms/ObjCARC/contract-rv-attr.ll
    M llvm/test/Transforms/ObjCARC/contract.ll
    M llvm/test/Transforms/ObjCARC/intrinsic-use.ll
    M llvm/test/Transforms/ObjCARC/rv.ll
    R llvm/test/Transforms/TailCallElim/deopt-bundle.ll
    A llvm/test/Transforms/TailCallElim/operand-bundles.ll

  Log Message:
  -----------
  [ObjC][ARC] Use operand bundle 'clang.arc.rv' instead of explicitly
emitting retainRV or claimRV calls in the IR

This reapplies 3fe3946d9a958b7af6130241996d9cfcecf559d4 without the
changes made to lib/IR/AutoUpgrade.cpp, which was violating layering.

Original commit message:

Background:

This patch makes changes to the front-end and middle-end that are
needed to fix a longstanding problem where llvm breaks ARC's autorelease
optimization (see the link below) by separating calls from the marker
instructions or retainRV/claimRV calls. The backend changes are in
https://reviews.llvm.org/D92569.

https://clang.llvm.org/docs/AutomaticReferenceCounting.html#arc-runtime-objc-autoreleasereturnvalue

What this patch does to fix the problem:

- The front-end adds operand bundle "clang.arc.rv" to calls, which
  indicates the call is implicitly followed by a marker instruction and
  an implicit retainRV/claimRV call that consumes the call result. In
  addition, it emits a call to @llvm.objc.clang.arc.noop.use, which
  consumes the call result, to prevent the middle-end passes from changing
  the return type of the called function. This is currently done only when
  the target is arm64 and the optimization level is higher than -O0.

- ARC optimizer temporarily emits retainRV/claimRV calls after the calls
  with the operand bundle in the IR and removes the inserted calls after
  processing the function.

- ARC contract pass emits retainRV/claimRV calls after the call with the
  operand bundle. It doesn't remove the operand bundle on the call since
  the backend needs it to emit the marker instruction. The retainRV and
  claimRV calls are emitted late in the pipeline to prevent optimization
  passes from transforming the IR in a way that makes it harder for the
  ARC middle-end passes to figure out the def-use relationship between
  the call and the retainRV/claimRV calls (which is the cause of
  PR31925).

- The function inliner removes an autoreleaseRV call in the callee if
  nothing in the callee prevents it from being paired up with the
  retainRV/claimRV call in the caller. It then inserts a release call if
  the call is annotated with claimRV since autoreleaseRV+claimRV is
  equivalent to a release. If it cannot find an autoreleaseRV call, it
  tries to transfer the operand bundle to a function call in the callee.
  This is important since ARC optimizer can remove the autoreleaseRV
  returning the callee result, which makes it impossible to pair it up
  with the retainRV/claimRV call in the caller. If that fails, it simply
  emits a retain call in the IR if the implicit call is a call to
  retainRV and does nothing if it's a call to claimRV.

Future work:

- Use the operand bundle on x86-64.

- Fix the auto upgrader to convert call+retainRV/claimRV pairs into
  calls annotated with the operand bundles.

rdar://71443534

Differential Revision: https://reviews.llvm.org/D92808