Move `rustc_middle::ty::Const` to `rustc_type_ir` Part 2 by Jamesbarford · Pull Request #163258 · rust-lang/rust

Jamesbarford · 2026-09-24T12:44:07Z

Split by commit;

Move all methods from ConstExt from rustc_middle, creating small helpers to aid this. Subsequently delete ConstExt.
Remove ConstExt from imports in compiler.
Remove ConstExt from imports in clippy.

r? lcnr

rustbot · 2026-09-24T12:44:10Z

rustc_codegen_cranelift is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_cranelift instead.

cc @bjorn3

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in rustc_ty_utils::consts.rs

cc @BoxyUwU

Some changes occurred in exhaustiveness checking

cc @Nadrieril

Some changes occurred in match checking

cc @Nadrieril

HIR ty lowering was modified

cc @fmease

Some changes occurred in match lowering

cc @Nadrieril

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

rustc_codegen_gcc is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_gcc instead.

cc @antoyo, @GuillaumeGomez

Some changes occurred in compiler/rustc_sanitizers

cc @rcvalle

RalfJung · 2026-09-25T08:13:28Z

Move Const from rustc_middle to rustc_type_ir

This is ty::Const, not mir::Const, right? Would be good to clarify so these PRs are easier to interpret. :)

lcnr · 2026-09-25T09:48:03Z

-        let valtree =
-            ty::ValTree::from_scalar_int(tcx, ScalarInt::try_from_uint(bits, size).unwrap());
-        ty::Const::new_value(tcx, valtree, ty)
-    }


this function is kind of scuffed :< I don't want this in rustc_type_ir if I am honest. More generally TypingEnv is in a weird state and I'd like to keep this out of rustc_type_ir for now 🤔 can we maybe keep this in an extension trait for now?

View changes since the review

Hmm what about on Interner;

fn const_from_bits(self, bits: u128, typing_env: Self::TypingEnv, ty: Self::Ty) -> Const<Self>;

Then keep the implementation in the rustc_middle's interner implementation? That way we don't need to resurrect the ConstExt and the scuffed parts stay in rustc_middle? Obviously happy to revert if that's a terrible idea.

I've given it a go in this commit; 39c689e, doesn't feel too bad as it uses a few interner methods

lcnr · 2026-09-25T09:50:53Z

+        } else {
+            const_v.try_to_leaf().map(|s| s.to_target_usize(self))
+        }
+    }


why exactly does this need to be on the interner? I guess the to_target_usize is the actually relevant part? 🤔

View changes since the review

Yes s.to_target_usize() to the relevant part. I've now made to_target_usize a method on ValueConst in inherent.rs. Could be less bad than bolting another helper method on to Interner?

I've done so in; bcc98fa

lcnr

lgtm modulo minor nits

View changes since this review

rustbot · 2026-10-06T08:10:47Z

Some changes occurred in compiler/rustc_codegen_llvm/src/debuginfo

cc @Walnut356

rustbot · 2026-10-06T08:10:50Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

lcnr · 2026-10-06T11:09:02Z

@@ -228,13 +227,21 @@ impl<'tcx> Value<'tcx> {
 }

 impl<'tcx> rustc_type_ir::inherent::ValueConst<TyCtxt<'tcx>> for Value<'tcx> {


future work, we should move Value into rustc_type_ir

View changes since the review

lcnr · 2026-10-06T11:14:46Z

my only question is const_from_bits /Const::from_bits. If this method only uses rustc_type_ir internal stuff, maybe we should have it on Const after all 🤔

Why do we need the TypingEnv extension trait again?

this is partially out of cache for me unfortunately 🤔

Jamesbarford · 2026-10-06T11:26:45Z

const_from_bits

const_from_bits exists so we aren't using TypingEnv in rustc_type_ir though maybe we could put something on the inherent trait for it to implement in rustc_middle?
The inherent trait is for I::TypingEnv::fully_monomorphized() so we can use it in Const::from_bool(...) and Const::from_target_usize(...)

lcnr · 2026-10-07T12:50:21Z

That's inconsistent, is it not. If we need to use TypingEnv::fully_monomorphized for two other functions, then const_from_bits being outside to avoid that doesn't really work, does it?

Either have all these functions outside of rustc_type_ir or all of them in it I'd say

…herent::TypingEnv`

Jamesbarford · 2026-10-08T07:36:00Z

That's inconsistent, is it not. If we need to use TypingEnv::fully_monomorphized for two other functions, then const_from_bits being outside to avoid that doesn't really work, does it?

Either have all these functions outside of rustc_type_ir or all of them in it I'd say

Good point, I've made a fn layout_size(...) on trait TypingEnv and moved fn from_bits(...) 0bf6c48

rust-bors · 2026-10-09T23:16:54Z

☔ The latest upstream changes (presumably #164052) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

lcnr · 2026-10-12T10:58:34Z

r=me after rebase

rustbot assigned lcnr Sep 24, 2026

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Jamesbarford changed the title ~~Move Const from rustc_middle to rustc_type_ir Part 2~~ Move rustc_middle::ty::Const to rustc_type_ir Part 2 Sep 25, 2026

lcnr reviewed Sep 25, 2026

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Comment thread compiler/rustc_middle/src/ty/consts/valtree.rs

lcnr reviewed Sep 25, 2026

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Comment thread compiler/rustc_type_ir/src/inherent.rs Outdated

lcnr reviewed Sep 25, 2026

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Jamesbarford force-pushed the chore/move-const-pt2 branch from 4f1d48f to 828380b Compare September 29, 2026 07:22

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Jamesbarford added 5 commits October 6, 2026 07:06

Move all Const methods to rustc_type_ir

ecd7838

Remove ConstExt from ./compiler

b01745b

Remove ConstExt from ./src

a2ed719

handle nits

d8e79de

create a const_from_bits(...) method

2255191

Jamesbarford force-pushed the chore/move-const-pt2 branch from 39c689e to 2255191 Compare October 6, 2026 08:10

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Remove ConstExt from clippy

7c053f6

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use panic! over bug!

5bdab32

lcnr reviewed Oct 6, 2026

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Remove const_from_bits off interner and create layout_size on `in…

0bf6c48

…herent::TypingEnv`

		@@ -228,13 +227,21 @@ impl<'tcx> Value<'tcx> {
		}

		impl<'tcx> rustc_type_ir::inherent::ValueConst<TyCtxt<'tcx>> for Value<'tcx> {

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