question: add index method for entities

[hsqStephenZhang]

I wonder if it's better to provide an index method or trait for the Value or BasicBlock since their number starts from a fixed NUMBER could not be created otherwise.
It would be helpful for generating more readable information like Debug trait for Value, or make it indexable for indexmap and so on. Cranelift and rustc both encode these entities in usize starting from 0 afaik.

for example

rustc_index::newtype_index! {
    #[debug_format = "bb{}"]
    pub struct BasicBlock {
        const START_BLOCK = 0;
    }
}

here is a usage when i'm generating dot file for the IR, it would be more readable to have value number starting from 0.

[MaxXSoft]

It's hard to change.

koopa/koopa/src/ir/idman.rs

Lines 57 to 60 in db080bd

	/// Returns `true` if the given value ID is a global value ID.
	pub(in crate::ir) fn is_global_id(value: ValueId) -> bool {
	value >= GLOBAL_VALUE_ID_STARTS_FROM && value < LOCAL_VALUE_ID_STARTS_FROM
	}

The IR framework determines whether a value ID corresponds to a global value by examining the range of that ID. That's why we need NameManager in the Koopa IR generator: https://github.com/pku-minic/koopa/blob/master/koopa/src/back/generator.rs

[hsqStephenZhang]

Got it. Maybe koopa could expose index method for Value and BasicBlock by subtract the range start?
(But that's only useful for nicer printing, user could use fxhashmap for better performance.)

[MaxXSoft]

Rewrite the Debug trait implementation is a better solution.