swiftlang/swift

[SR-6979] ThinToThickFunction derived pointers do not need to be retained/released

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#49,527 opened on 2018年2月11日

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bugcompilergood first issueperformance

説明
Previous ID SR-6979
Radar None
Original Reporter @gottesmm
Type Bug
Votes 0
Component/s Compiler
Labels Bug, Performance, StarterBug
Assignee None
Priority Medium

md5: 570977381e8bce3c10e08267eb895f6f

Issue Description:

I was reading some SIL recently:

  debug_value undef : $Error, var, name "$error", argno 1 // id: %0                                                               
  // function_ref thrower()                                                                                                       
  %1 = function_ref @$S8rethrows7throwerSiyKF : $@convention(thin) () -> (Int, @error Error) // user: %2                          
  %2 = thin_to_thick_function %1 : $@convention(thin) () -> (Int, @error Error) to $@callee_guaranteed () -> (Int, @error Error) \
// user: %3                                                                                                                       
  %3 = convert_function %2 : $@callee_guaranteed () -> (Int, @error Error) to $@noescape @callee_guaranteed () -> (Int, @error Er\
ror) // users: %11, %7, %5                                                                                                        
  // function_ref rethrower(_:)                                                                                                   
  %4 = function_ref @$S8rethrows9rethroweryS2iyKXEKF : $@convention(thin) (@guaranteed @noescape @callee_guaranteed () -> (Int, @\
error Error)) -> (Int, @error Error) // user: %5                                                                                  
  try_apply %4(%3) : $@convention(thin) (@guaranteed @noescape @callee_guaranteed () -> (Int, @error Error)) -> (Int, @error Erro\
r), normal bb1, error bb2 // id: %5                                                                                               
                                                                                                                                  
bb1(%6 : $Int):                                   // Preds: bb0                                                                   
  strong_release %3 : $@noescape @callee_guaranteed () -> (Int, @error Error) // id: %7
  ...

%7 should be able to be removed. I imagine though this peephole would need to be done late in the pipeline since it breaks semantic sil invariants.

コントリビューターガイド

技術スタック
swift
領域
performance
Issue 種別
bug
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
3
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
half day
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
fresh
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
SIL knowledgecompiler optimization basics
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
70
調査方針
Investigate the SIL optimization passes in the Swift compiler, particularly those that handle thin to thick function. The issue points out that a strong release on a @noescape @callee guaranteed function is unnecessary because thin to thick derived pointers do not need to be retained/released. Look at the SILOptimizer directory (e.g., lib/SILOptimizer/) for existing peephole optimizations (like RedundantLoadElimination or similar) and determine where to add this removal. Consider that the optimization must be placed late in the pipeline to avoid breaking semantic SIL invariants. The issue has no assignee or comments, making it a good candidate for a first contribution.