Stephen Tozer 0863bd83e5 [LLVM] Add option to store Parent-pointer in ilist_node_base (#94224) ...

This patch adds a new option for `ilist`, `ilist_parent<ParentTy>`, that
enables storing an additional pointer in the `ilist_node_base` type to a
specified "parent" type, and uses that option for `Instruction`.

This is distinct from the `ilist_node_with_parent` class, despite their
apparent similarities. The `ilist_node_with_parent` class is a subclass
of `ilist_node` that requires its own subclasses to define a `getParent`
method, which is then used by the owning `ilist` for some of its
operations; it is purely an interface declaration. The `ilist_parent`
option on the other hand is concerned with data, adding a parent field
to the `ilist_node_base` class.

Currently, we can use `BasicBlock::iterator` to insert instructions,
_except_ when either the iterator is invalid (`NodePtr=0x0`), or when
the iterator points to a sentinel value (`BasicBlock::end()`). This patch
results in the sentinel value also having a valid pointer to its owning
basic block, which allows us to use iterators for all insertions,
without needing to store or pass an extra `BasicBlock *BB` argument
alongside it.

2024-06-18 19:59:35 +01:00

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