This uint will be used for the following:
- Since SM4's relative addressing (the capability of passing a register
as an index to another register) only has whole-register granularity,
we will need to make the offset node express the offset in
whole-registers and specify the register component in this uint,
otherwise we would have to add additional / and % operations in the
output binary.
- If, after we apply constant folding and copy propagation, we determine
that the offset is a single constant node, we can store all the offset
in this uint constant, and remove the offset src.
This allows DCE to remove a good bunch of the nodes previously required
only for the offset constants, which makes the output more liteweight
and readable, and simplifies the implementation of relative addressing
when writing tpf in the following patches.
In dump_deref(), we use "c" to indicate components instead of whole
registers. Since now both the offset node and the offset uint are in
components a lowered deref would look like:
var[@42c + 2c]
But, once we express the offset node in whole registers we will remove
the "c" from the node part:
var[@22 + 3c]
Some functions work with dereferences and need to know if they are
lowered yet.
This can be known checking if deref->offset.node is NULL or
deref->data_type is NULL. I am using the latter since it keeps working
even after the following patches that split deref->offset into
constant and variable parts.
