LLVM结构返回优化

问题描述

我想知道为什么LLVM无法优化以下IR代码(使用PassManagerBuilder(优化设置为"3"，还使用LLVM的"opt"工具):

I'm wondering why LLVM fails to optimize the following IR code (using the PassManagerBuilder with optimisation set to '3', and also using LLVM's 'opt' tool):

%GenericStruct = type { i32 }

define void @makeGenericStructOuter(%GenericStruct* noalias nocapture sret) {
entry:
  %1 = alloca %GenericStruct
  call void @makeGenericStructInner(%GenericStruct* %1)
  %2 = load %GenericStruct* %1
  store %GenericStruct %2, %GenericStruct* %0
  ret void
}

declare void @makeGenericStructInner(%GenericStruct* noalias nocapture sret)

期望的代码是:

%GenericStruct = type { i32 }

define void @makeGenericStructOuter(%GenericStruct* noalias nocapture sret) {
entry:
  call void @makeGenericStructInner(%GenericStruct* %0)
  ret void
}

declare void @makeGenericStructInner(%GenericStruct* noalias nocapture sret)

目前是否没有优化可用于处理这种情况?还是我无法生成(该代码是从我正在开发的前端生成的)正确的IR(允许进行优化)?

Are there simply no optimizations currently available to handle this case? Or am I failing to produce (this code is generated from a front-end I'm developing) the right IR that would allow optimization?

在建议之前，我无法生成按值返回的代码，因为这些函数必须可以从其他不知道'GenericStruct'大小或内容的模块/库中调用(它们将在本地声明'TestClass'为结构不透明").

Before it's suggested, I can't produce code that returns by value since these functions must be callable from other modules/libraries that don't know the size or contents of 'GenericStruct' (and they would locally declare 'TestClass' as 'struct opaque').

推荐答案

如果您认为应该进行优化，请在 LLVM Bug Tracker .当错过报告优化机会时，LLVM开发人员通常会非常高兴和感兴趣.

If you belive that optimization should take place, report a bug in LLVM Bug Tracker. LLVM developers are usually very happy and interested when reporting optimization opportunities missed.

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