bc888958c9
Allow MIR debuginfo to point to a variable's address MIR optimizations currently do not to operate on borrowed locals. When enabling #106285, many borrows will be left as-is because they are used in debuginfo. This pass allows to replace this pattern directly in MIR debuginfo: ```rust a => _1 _1 = &raw? mut? _2 ``` becomes ```rust a => &_2 // No statement to borrow _2. ``` This pass is implemented as a drive-by in ReferencePropagation MIR pass. This transformation allows following following MIR opts to treat _2 as an unborrowed local, and optimize it as such, even in builds with debuginfo. In codegen, when encountering `a => &..&_2`, we create a list of allocas: ```llvm store ptr %_2.dbg.spill, ptr %a.ref0.dbg.spill store ptr %a.ref0.dbg.spill, ptr %a.ref1.dbg.spill ... call void `@llvm.dbg.declare(metadata` ptr %a.ref{n}.dbg.spill, /* ... */) ``` Caveat: this transformation looses the exact type, we do not differentiate `a` as a immutable, mutable reference or a raw pointer. Everything is declared to `*mut` to codegen. I'm not convinced this is a blocker.
Please read the rustc-dev-guide chapter on Backend Agnostic Codegen.