Details
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Bug
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Status: Resolved
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Major
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Resolution: Fixed
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None
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None
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ghx-label-7
Description
The function template CodegenFnPtr<FuncType>::store() tries to implicitly cast a function pointer (of type FuncType) to void*, which is a compile time error. The reason this didn't come up in the builds is that this function template is currently not used anywhere, and the function pointers are stored through the parent class, using CodegenFnPtrBase::store(), which takes a void*.
We should either
- remove the hitherto unused CodegenFnPtr<FuncType>::store() function template
OR - add the correct explicit cast from function pointer to void* AND add a test which instantiates (and tests) this function template so we can be sure that the new implementation is correct.
I'm inclined to choose the second option because I think the interface of CodegenFnPtr<FuncType> is more complete if we have this function as well, even if it is currently not used.
Note:
After digging a bit on the internet I found that the reason that implicit function pointer to void* cast is not allowed (as opposed to implicit regular pointer to void*) is because the standard doesn't guarantee that regular and function pointers have the same size, and there are some architectures where they actually don't.
However, according to 8) on https://en.cppreference.com/w/cpp/language/reinterpret_cast, POSIX compliant systems do have this guarantee, so it shouldn't be a problem that we store function pointers as void*. We don't really have a choice because LLVM does the same as llvm::ExecutionEngine::getPointerToFunction() returns a void* (see https://llvm.org/doxygen/classllvm_1_1ExecutionEngine.html#acc46759a6acfc3d116c3f22110326ffa); we call that function here.