Patterns: represent constants as valtrees #144591

RalfJung · 2025-07-28T16:23:45Z

Const patterns are always valtrees now. Let's represent that in the types.

It turns out we do have to carry along the type with the valtree (many places have another ty somewhere, but it's not always the same type, and I wasn't able to disentangle this). We could use ty::Value which nicely pairs up a valtree and a value -- however, a const pattern can be a raw pointer, which is not a valid "type system value". So I went for separate fields instead. I think by now I am regretting that choice, but I decided to wait what the reviewer would say. Using Value would avoid risking mixing the valtree with the wrong type. It also has some convenient methods, though TBH they aren't very needed here since they often double-check the type which is unnecessary work most of the time.

Cc @Nadrieril @BoxyUwU

rustbot · 2025-07-28T16:23:49Z

r? @fee1-dead

rustbot has assigned @fee1-dead.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

rustbot · 2025-07-28T16:23:51Z

Some changes occurred in rustc_ty_utils::consts.rs

cc @BoxyUwU

Some changes occurred in match lowering

cc @Nadrieril

Some changes occurred in exhaustiveness checking

cc @Nadrieril

Some changes occurred in match checking

cc @Nadrieril

RalfJung · 2025-07-28T16:25:07Z

compiler/rustc_mir_build/src/builder/matches/test.rs

                let tcx = self.tcx;
                let success_block = target_block(TestBranch::Success);
                let fail_block = target_block(TestBranch::Failure);

-                let mut expect_ty = value.ty();
+                let mut expect_ty = value_ty;
+                let value = Const::Ty(value_ty, ty::Const::new_value(tcx, value, value_ty));


Oddly, constructing a mir::Const from a valtree requires the type twice...

Const::Ty storing more than just a ty::Const is kinda meh yeah. This came about when we stopped storing a Ty alongside all ty::Consts. Removing the ty field from Const::Ty would require updating the function mir::Const::ty( to take either a TypingEnv so we can lookup the type of const parameters, and so that we can normalize the resulting type from type_of unevaluated constants and const generic parameter declarations

It is odd that mir::Const and ty::Value know their type but ty::Const does not... but I won't touch this now, there's probably a reason we ended up here.^^

you can likely find a bit of context in #125958 as to how ty::Const wound up the way it did. For ty::Const only ty::Value needs a Ty because everything else we can "figure out" the type from the environment we're in or from the ty::Const itself.

I would expect that mir::Const::Unevaluated doesnt really need to store a Ty either as it should just be equivalent to type_of(uv.def).instantiate(uv.args) and then a normalization call 🤔

tests/ui/thir-print/thir-tree-loop-match.stdout

RalfJung · 2025-07-28T16:31:39Z

compiler/rustc_pattern_analysis/src/rustc.rs

+                let max = ty.numeric_max_val(cx.tcx).unwrap();
+                let max = ty::ValTree::from_scalar_int(cx.tcx, max.try_to_scalar_int().unwrap());


This is a kind of silly dance. Maybe numeric_max_val should just return a ScalarInt?

RalfJung · 2025-07-28T21:18:04Z

@rust-timer queue
@bors try

rust-bors · 2025-07-28T21:18:07Z

⌛ Trying commit b39c019 with merge e111586…

To cancel the try build, run the command @bors try cancel.

Patterns: represent constants as valtrees

rust-bors · 2025-07-28T23:33:17Z

☀️ Try build successful (CI)
Build commit: e111586 (e1115864e9f2387f19e755d0a8a30df5a8933f7c, parent: e3514bde96d2d13586337a48db77fa64b850d249)

BoxyUwU · 2025-07-29T00:41:21Z

We could use ty::Value which nicely pairs up a valtree and a value -- however, a const pattern can be a raw pointer, which is not a valid "type system value".

Given that we evaluate all const patterns by going through a ty::Const or ty::UnevaluatedConst we already don't get the property that ty::Const s only have to deal with stuff in const generics. I'm not sure if this is desirable or not and I think I need to finish adt_const_params before I'll be able to tell for sure 🤔

Regardless, with this in mind I think using ty::Value is fine, we can always swap it out for a different Ty/ValTree tuple down the road if it winds up being a problem. It doesn't seem worth making code-quality worse in order to try and maintain a property that doesn't even hold rn and I don't know how we even would do so nicely :D

rust-timer · 2025-07-29T01:02:57Z

Finished benchmarking commit (e111586): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.0%	[-2.8%, -0.1%]	7
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.0%	[-2.8%, -0.1%]	7

Max RSS (memory usage)

Results (secondary -0.8%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.3%	[2.3%, 2.3%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-3.1%, -2.7%]	3
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -3.3%, secondary 2.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.3%	[2.3%, 2.3%]	1
Improvements ✅ (primary)	-3.3%	[-3.3%, -3.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.3%	[-3.3%, -3.3%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 468.526s -> 467.78s (-0.16%)
Artifact size: 376.81 MiB -> 376.82 MiB (0.00%)

RalfJung · 2025-07-29T07:01:42Z

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -907,7 +891,7 @@ impl<'p, 'tcx: 'p> PatCx for RustcPatCtxt<'p, 'tcx> {
    type Ty = RevealedTy<'tcx>;
    type Error = ErrorGuaranteed;
    type VariantIdx = VariantIdx;
-    type StrLit = Const<'tcx>;
+    type StrLit = ty::Value<'tcx>;


Oddly it seems like I can just change this type and nobody cares...

RalfJung · 2025-07-29T07:03:57Z

compiler/rustc_mir_build/src/builder/matches/mod.rs

@@ -1373,16 +1373,16 @@ enum TestBranch<'tcx> {
    /// Success branch, used for tests with two possible outcomes.
    Success,
    /// Branch corresponding to this constant.
-    Constant(Const<'tcx>, u128),
+    Constant(ty::Value<'tcx>, u128),


This is the one place where dropping the type and just using a ValTree would work... but for consistency I kept it here, too.

RalfJung · 2025-07-29T07:04:33Z

@bors try
@rust-timer queue

RalfJung · 2025-07-29T11:36:52Z

@bors try

rust-bors · 2025-07-29T11:36:57Z

⌛ Trying commit 3ebc541 with merge 44fbf1c…

(The previously running try build was automatically cancelled.)

To cancel the try build, run the command @bors try cancel.

Patterns: represent constants as valtrees

RalfJung · 2025-07-29T11:37:52Z

compiler/rustc_mir_build/src/builder/matches/test.rs

-                    let bits = value.eval_bits(self.tcx, self.typing_env());
-                    Some(TestBranch::Constant(value, bits))
+                    let bits = value.try_to_scalar_int().unwrap().to_bits_unchecked();
+                    Some(TestBranch::Constant(value.valtree, bits))


Something very odd is happening here... this seems to be the only place that constructs a TestBranch::Constant, so bits here is always the result of calling unwrap_leaf().to_bits_unchecked() on the valtree. So, uh, why do we store both the valtree and its bits?

RalfJung · 2025-07-29T11:42:06Z

@bors try

Patterns: represent constants as valtrees

rust-bors · 2025-07-29T11:42:11Z

⌛ Trying commit 0a1ffd9 with merge 7380d99…

(The previously running try build was automatically cancelled.)

To cancel the try build, run the command @bors try cancel.

rust-bors · 2025-07-29T13:58:31Z

☀️ Try build successful (CI)
Build commit: 7380d99 (7380d99b508c50a3825bd54044d573ec8dd97f5f, parent: 552904134b564a74489db50aebe7070fdcce895c)

rust-timer · 2025-07-29T15:10:08Z

Finished benchmarking commit (7380d99): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.9%	[0.8%, 1.0%]	6
Improvements ✅ (primary)	-2.3%	[-3.3%, -0.1%]	7
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-3.3%, -0.1%]	7

Max RSS (memory usage)

Results (primary 3.7%, secondary -0.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.7%	[3.7%, 3.7%]	1
Regressions ❌ (secondary)	2.6%	[2.5%, 2.7%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-4.7%, -1.9%]	4
All ❌✅ (primary)	3.7%	[3.7%, 3.7%]	1

Cycles

Results (primary -0.2%, secondary 4.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	4.6%	[4.5%, 4.7%]	2
Improvements ✅ (primary)	-2.7%	[-2.7%, -2.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-2.7%, 2.3%]	2

Binary size

Results (secondary -0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-	-	0

Bootstrap: 468.885s -> 469.633s (0.16%)
Artifact size: 376.79 MiB -> 376.87 MiB (0.02%)

RalfJung · 2025-07-29T15:23:15Z

@bors try
@rust-timer queue

rust-bors · 2025-07-29T15:23:20Z

⌛ Trying commit cbb5fc1 with merge 51ac280…

To cancel the try build, run the command @bors try cancel.

Patterns: represent constants as valtrees

rust-bors · 2025-07-29T17:38:44Z

☀️ Try build successful (CI)
Build commit: 51ac280 (51ac2805763b973371abc5ea5c9aced2149b18c6, parent: 7278554d82fa474a4e8b5c67afb009e11e41a841)

rust-timer · 2025-07-29T19:46:53Z

Finished benchmarking commit (51ac280): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.9%	[0.8%, 1.0%]	6
Improvements ✅ (primary)	-2.7%	[-3.3%, -2.1%]	6
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.7%	[-3.3%, -2.1%]	6

Max RSS (memory usage)

Results (primary -1.3%, secondary -1.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-2.6%	[-2.8%, -2.2%]	3
All ❌✅ (primary)	-1.3%	[-1.3%, -1.3%]	1

Cycles

Results (secondary 2.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 467.638s -> 467.767s (0.03%)
Artifact size: 376.88 MiB -> 376.87 MiB (-0.00%)

RalfJung · 2025-07-29T20:18:35Z

Well, uh, I don't know why this could be slower than the version with separate types and valtrees...

fee1-dead · 2025-08-02T15:14:24Z

r? BoxyUwU

rustbot · 2025-08-02T15:14:29Z

BoxyUwU is currently at their maximum review capacity.
They may take a while to respond.

PatKind: store constants as valtrees

ebe74a2

rustbot assigned fee1-dead Jul 28, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 28, 2025

RalfJung changed the title ~~Pattern valtrees~~ Patterns: represent constants as valtrees Jul 28, 2025

RalfJung commented Jul 28, 2025

View reviewed changes

tests/ui/thir-print/thir-tree-loop-match.stdout Outdated Show resolved Hide resolved

RalfJung commented Jul 28, 2025

View reviewed changes

pattern testing: store constants as valtrees

b39c019

RalfJung force-pushed the pattern-valtrees branch from ee610cc to b39c019 Compare July 28, 2025 16:33

RalfJung mentioned this pull request Jul 28, 2025

Raw Pointers are Constant PatKinds too #144573

Merged

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Jul 28, 2025

Auto merge of #144591 - RalfJung:pattern-valtrees, r=<try>

e111586

Patterns: represent constants as valtrees

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 28, 2025

This comment has been minimized.

Sign in to view

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 29, 2025

use ty::Value instead of manual pairs of types and valtrees

1870bd2

RalfJung force-pushed the pattern-valtrees branch from 52c6e8f to 1870bd2 Compare July 29, 2025 06:58

change StrLit type to ty::Value as well

9f3f015

RalfJung commented Jul 29, 2025

View reviewed changes

This comment has been minimized.

Sign in to view

RalfJung force-pushed the pattern-valtrees branch from 36591d9 to 3ebc541 Compare July 29, 2025 11:36

rust-bors bot added a commit that referenced this pull request Jul 29, 2025

Auto merge of #144591 - RalfJung:pattern-valtrees, r=<try>

44fbf1c

Patterns: represent constants as valtrees

RalfJung commented Jul 29, 2025

View reviewed changes

RalfJung force-pushed the pattern-valtrees branch from 3ebc541 to 0a1ffd9 Compare July 29, 2025 11:41

rust-bors bot added a commit that referenced this pull request Jul 29, 2025

Auto merge of #144591 - RalfJung:pattern-valtrees, r=<try>

7380d99

Patterns: represent constants as valtrees

shrink TestBranch::Constant and PatRangeBoundary::Finite

5e53d76

RalfJung force-pushed the pattern-valtrees branch from 0a1ffd9 to 5e53d76 Compare July 29, 2025 11:43

This comment has been minimized.

Sign in to view

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 29, 2025

avoid unnecessary type sanity checks

cbb5fc1

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Jul 29, 2025

Auto merge of #144591 - RalfJung:pattern-valtrees, r=<try>

51ac280

Patterns: represent constants as valtrees

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 29, 2025

This comment has been minimized.

Sign in to view

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 29, 2025

rustbot assigned BoxyUwU and unassigned fee1-dead Aug 2, 2025

		let max = ty.numeric_max_val(cx.tcx).unwrap();
		let max = ty::ValTree::from_scalar_int(cx.tcx, max.try_to_scalar_int().unwrap());

Patterns: represent constants as valtrees #144591

Are you sure you want to change the base?

Patterns: represent constants as valtrees #144591

Conversation

RalfJung commented Jul 28, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Jul 28, 2025

Uh oh!

rustbot commented Jul 28, 2025

Uh oh!

Choose a reason for hiding this comment

Uh oh!

BoxyUwU Jul 29, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

BoxyUwU Jul 29, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

RalfJung commented Jul 28, 2025

Uh oh!

This comment has been minimized.

rust-bors bot commented Jul 28, 2025

Uh oh!

rust-bors bot commented Jul 28, 2025

Uh oh!

This comment has been minimized.

BoxyUwU commented Jul 29, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rust-timer commented Jul 29, 2025

Overall result: ✅ improvements - no action needed

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

RalfJung commented Jul 29, 2025

Uh oh!

This comment has been minimized.

RalfJung commented Jul 29, 2025

Uh oh!

rust-bors bot commented Jul 29, 2025

Uh oh!

RalfJung Jul 29, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

RalfJung commented Jul 29, 2025

Uh oh!

rust-bors bot commented Jul 29, 2025

Uh oh!

rust-bors bot commented Jul 29, 2025

Uh oh!

This comment has been minimized.

rust-timer commented Jul 29, 2025

Overall result: ❌✅ regressions and improvements - please read the text below

Uh oh!

RalfJung commented Jul 29, 2025

Uh oh!

This comment has been minimized.

rust-bors bot commented Jul 29, 2025

Uh oh!

rust-bors bot commented Jul 29, 2025

Uh oh!

This comment has been minimized.

rust-timer commented Jul 29, 2025

Overall result: ❌✅ regressions and improvements - please read the text below

Uh oh!

RalfJung commented Jul 29, 2025

Uh oh!

fee1-dead commented Aug 2, 2025

Uh oh!

RalfJung commented Jul 28, 2025 •

edited

Loading

BoxyUwU Jul 29, 2025 •

edited

Loading

BoxyUwU Jul 29, 2025 •

edited

Loading

BoxyUwU commented Jul 29, 2025 •

edited

Loading

RalfJung Jul 29, 2025 •

edited

Loading