Allow MIR debuginfo to point to a variable's address by cjgillot · Pull Request...
source link: https://github.com/rust-lang/rust/pull/111440
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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:
a => _1
_1 = &raw? mut? _2becomes
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:
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.
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