[cfe-dev] Named Registers Impl

[Renato Golin]

Folks,

I started implementing the named registers in Clang and was presented
with the nice fact that it's mostly there. At least, all the way to
the AST is all good, but the IR emission, as expected, is still
ignoring the register/asm part of the variable.

So, the idea is to transform all reads from that variable to
@llvm.read_register and all writes to @llvm.write_register. I can
think of two ways of doing this:

1. On Sema::ActOnVariableDeclarator(), on the switch detecting named
register variables, I set the initialization to a call to the
intrinsic. That's pretty high level, but it's where we diagnose bad
register names and where we have most of the information we need. Some
fiddling with the return value will be necessary.

2. Down on CodeGenFunction::EmitDeclRefLValue(), using a previously
set flag (isNamedReg), I replace the lowering of the variable (which
was not initialised in CodeGenFunction::EmitAutoVarAlloca()) by
EmitFunctionDeclLValue(intrinsic, etc). This will require no fiddling
with the return values, but will pass down info until much later.

Is there another way? If not, what is the preferred one?

Thanks,
--renato