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[SR-13459] type metadata accessor for private swift-native class should be a single memory access #55901

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dabrahams opened this issue Aug 27, 2020 · 2 comments
Closed

[SR-13459] type metadata accessor for private swift-native class should be a single memory access #55901

dabrahams opened this issue Aug 27, 2020 · 2 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself

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@dabrahams
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Previous ID SR-13459
Radar None
Original Reporter @dabrahams
Type Bug
Status Resolved
Resolution Invalid
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: 5dfac902494d755369487814799729ee

relates to:

  • SR-13469 Call to objc_opt_self slows access to non-generic class metadata

Issue Description:

Instead it compiles into two function calls

private class X {}
func disassembleMe() -> Any.Type {
  return X.self
}

becomes:

x.disassembleMe() -> Any.Type:
    pushq   %rbp
    movq    %rsp, %rbp
    xorl    %edi, %edi
    popq    %rbp
    jmp type metadata accessor for x.(X in _613077CFEB536AFE339AC751B60607CD)

    .p2align    4, 0x90
type metadata accessor for x.(X in _613077CFEB536AFE339AC751B60607CD):
    pushq   %rax
    leaq    full type metadata for x.(X in _613077CFEB536AFE339AC751B60607CD)+16(%rip), %rdi
    callq   _objc_opt_self
    xorl    %edx, %edx
    popq    %rcx
    retq

/cc @eeckstein
@dabrahams
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We can't eliminate the call because of objc interop 🙁.
Best we could do is store the result in a `static let`, but I can do that manually.

@dabrahams
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FWIW, for my use case, the `static let`is a significant speedup.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself
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@dabrahams