pub enum Address {
BaseIndexScale,
IndexScale,
Base,
BaseOffset,
}Expand description
What an address constructor’s arguments are.
An addressing mode is an argument to an instruction rather than an instruction, and a rule
file writes one as a term so that a rule can say which registers go where. The selector has
to turn that term into a machine IR memory operand, and what each constructor’s arguments
mean is the same kind of target fact as Form, so it is written here rather than in the
selector.
The scale and the displacement are arguments rather than part of the name because each is a number the rule matched and the machine encodes it as a number. There is none with a symbol yet, because the rules that would need one are the ones about a global and those are not written.
What the arguments mean is the whole of what tells these apart, and there is deliberately no predicate here that answers half the question: the same register is a base in one of these and an index in another, and the same constant is a scale in one and a displacement in another, so anything building an address out of one has to look at which it is.
Variants§
BaseIndexScale
A base register, an index register and a scale, in that order.
IndexScale
An index register and a scale, which is an address with nothing to add it to.
Base
A base register on its own, which is what a pointer already in a register is.
BaseOffset
A base register and a constant added to it, which is every field of a structure and every local reached through a frame pointer.