Constructing a string_view from string literal uses a call to strlen

[rmn30]

The following code will emit a call to strlen:

std::string_view a {"hello"};

This is a bit surprising because it could be evaluated at compile time. It's slightly annoying because it might require adding the 'strings' library on CHERIoT and obviously is slightly suboptimal from a performance point of view. Using a string_view literal doesn't require this call e.g.

using namespace std::literals;
std::string_view a {"hello"sv};

This is by no means urgent and may be an upstream issue but thought it worth noting.

[resistor]

This is happening because of our name mangling. The C++ name mangling that we apply to all symbols causes LLVM’s libcall simplification pass not to recognize and optimize the call to strlen.

There’s a few options here: I can teach LLVM to handle the mangled version, but it will take a good bit of code if we want that to work for all the libcalls that LLVM can optimize.

Alternatively, we can evaluate whether we should move to unmangled names for some of these libc symbols, as we do for memcpy, etc.

[resistor]

CHERIoT-Platform/cheriot-rtos#455 is the final piece to fix this.