为什么 Module::getOrInsertFunction returns 指向常量的指针
Why Module::getOrInsertFunction returns a pointer to Constant
在 LLVM 中 Module::getOrInsertFunction 有 4 个如下所示的变体，并且全部 returns Constant*。为什么创建 Function 时返回指向 Constant 的指针？
Constant * getOrInsertFunction (StringRef Name, FunctionType *T, AttributeSet AttributeList)
documentation 内容为：
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，return 的值是 ConstantExpr*，而不是 Function*。因此，return 类型是 Constant*，公共超类。
在 LLVM 中 Module::getOrInsertFunction 有 4 个如下所示的变体，并且全部 returns Constant*。为什么创建 Function 时返回指向 Constant 的指针？
Constant * getOrInsertFunction (StringRef Name, FunctionType *T, AttributeSet AttributeList)
documentation 内容为：
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，return 的值是 ConstantExpr*，而不是 Function*。因此，return 类型是 Constant*，公共超类。