[clang] No way to generate addrspacecast with C++ style cast

[choikwa]

https://godbolt.org/z/zbrTTqMPv demonstrates C++ casts (static_cast, reinterpret_cast, etc) can't be used to generate addrspacecast. Only C style cast is lowered to addrspacecast. This is important for noalias analysis as addrspacecast is needed (vs PtrToInt) for ptr provenance and set appropriate alias.scope.

A typical scenario may be using reinterpret_cast<AS(n) T*>(reinterpret_cast<uintptr_t>(ptr)) but this inadvertently generates PtrToInt and IntToPtr which is considered as 'capturing' the pointer and llvm cannot trace it back to the underlying objects.

[llvmbot]

@llvm/issue-subscribers-c-1

Author: choikwa (choikwa)

https://godbolt.org/z/zbrTTqMPv demonstrates C++ casts (static_cast, reinterpret_cast, etc) can't be used to generate addrspacecast. Only C style cast is lowered to addrspacecast. This is important for noalias analysis as addrspacecast is needed (vs PtrToInt) for ptr provenance and set appropriate alias.scope.

A typical scenario may be using reinterpret_cast<AS(n) T*>(reinterpret_cast<uintptr_t>(ptr)) but this inadvertently generates PtrToInt and IntToPtr which is considered as 'capturing' the pointer and llvm cannot trace it back to the underlying objects.

[frederick-vs-ja]

I guess this is intended.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: choikwa (choikwa)

https://godbolt.org/z/zbrTTqMPv demonstrates C++ casts (static_cast, reinterpret_cast, etc) can't be used to generate addrspacecast. Only C style cast is lowered to addrspacecast. This is important for noalias analysis as addrspacecast is needed (vs PtrToInt) for ptr provenance and set appropriate alias.scope.

A typical scenario may be using reinterpret_cast<AS(n) T*>(reinterpret_cast<uintptr_t>(ptr)) but this inadvertently generates PtrToInt and IntToPtr which is considered as 'capturing' the pointer and llvm cannot trace it back to the underlying objects.