llvm - 为什么 Module::getOrInsertFunction 返回一个指向 Constant 的指针

Question

LLVM 中的 Module::getOrInsertFunction 有如下 4 种变体，它们都返回 Constant*。为什么在创建 Function 时返回指向 Constant 的指针？

常量 * getOrInsertFunction (StringRef Name, FunctionType *T, AttributeSet AttributeList)

Answer 1

documentation阅读:

Four possibilities: 1. If it does not exist, add a prototype for the function and return it. 2. If it exists, and has a local linkage, the existing function is renamed and a new one is inserted. 3. Otherwise, if the existing function has the correct prototype, return the existing function. 4. Finally, the function exists but has the wrong prototype: return the function with a constantexpr cast to the right prototype.

对于情况 4，返回值是 ConstantExpr*，而不是 Function*。因此，返回类型是 Constant*，即公共(public)父类(super class)。