Migrate validation from `maxInterStageShaderComponents` to `maxInterStageShaderVariables` (minus coverage of `clip-distances`) #8652

ErichDonGubler · 2025-12-03T22:56:44Z

Recommended review experience is commit-by-commit.

Connections

Fixes part of Update inter-stage interface validation to follow spec #5577.
maxInterStageShaderVariables was originally discussed for introduction to the WebGPU spec. committee at Should we constrain the location of user input-output stage variables WGSL gpuweb/gpuweb#1962.
maxInterStageShaderVariables was proposed to outright supersede maxInterStageShaderComponents with maxInterStageShaderComponents seems to overlap with maxInterStageShaderVariables gpuweb/gpuweb#4688.
See also Add note to WebGPU spec explaining what limits the number of WGSL @locations. gpuweb/gpuweb#4077.
clip-distances validation is scoped to Add clip distances validation for maxInterStageShaderVariables #8762.

Testing

CTS tests have been enabled that previously failed.

Squash or Rebase?

Rebase.

wgpu-core/src/validation.rs

ErichDonGubler · 2025-12-22T19:27:44Z

Oh, wow. When I'm running CTS for non-async render pipeline creation to validate this, tens of megabytes get allocated per second…until the DX12 backend very reasonably OOMs. 😐 I think I'm going to punt on getting full test coverage on this, and just cherry-pick a few ones I think are most important.

I don't plan on changing any end-state code at this point—just test coverage and commit structure—so I think this is ready for review.

ErichDonGubler · 2025-12-22T19:28:10Z

@andyleiserson said he'd review this in an internal Mozilla meeting today. ❤️

ErichDonGubler · 2025-12-22T19:29:38Z

wgpu-core/src/validation/shader_io_deductions.rs

+    SubgroupSize,
+
+    // Non-standard
+    // TODO: Is this list actually good?


Wanted to explicitly call out a request for reviewer opinion here. Particularly important to get right is (1) what this set actually is, and (2) how much space each built-in should take up.

Based on the commentary on variants of naga::BuiltIn and some skimming of built-in implementation to (non-exhaustively) confirm things, I believe this is correct.

cts_runner/test.lst

ErichDonGubler · 2025-12-22T22:26:48Z

Hmm, I noticed that running the …,maxInterStageShaderVariables:createRenderPipeline,at_over:… in CTS locally led to OOM errors on Vulkan, and actual OOMs within a few minutes of (very slow) execution on DX12. I haven't tested macOS, but that's a barrier to running these tests for contributors that we shouldn't accept.

EDIT: Filed #8777.

andyleiserson

andyleiserson · 2025-12-20T01:59:10Z

wgpu-types/src/limits.rs

            max_compute_workgroup_size_z: 0,
            max_compute_workgroups_per_dimension: 0,

            // Value supported by Intel Celeron B830 on Windows (OpenGL 3.1)


Suggested change

// Value supported by Intel Celeron B830 on Windows (OpenGL 3.1)

// Intel Celeron B830 on Windows (OpenGL 3.1) supports up to 31 bytes (~8 variables)

(Or delete it entirely. It feels like a shame to lose the research but it may not be worth maintaining.)

I don't know if this is bytes and words, or words and vec4s.

@kpreid is the author of this code originally, so let's ping him and ask! Kevin, Do you recall what the actual capabilities are here? If we need to, then this is an interesting conflict with the spec., in which even compatibility mode only lowers the minimum support required to 15. I'm guessing that, as @andyleiserson suspects, we should only allow 8 variables here?

I'll file an issue and follow-up if there are changes we need to make here before releasing. I'm still gonna merge, tho.

wgpu-hal/src/gles/adapter.rs

cts_runner/test.lst

wgpu-core/src/validation.rs

…function

…erStage` This will better prepare for the subsequent commit, which supplants `naga::ShaderStage` as the source of truth in this code.

ErichDonGubler · 2025-12-23T20:12:44Z

I've added a CHANGELOG entry for this PR with e0d67c8.

…orValidation` In order to prepare for spec.-compliant validation of shader I/O, we need to create a new `enum` that will have the same set of _variants_ as `naga::ShaderStage`, but will carry additional information relevant to validation. As a preparatory step, create the new `enum` (called `ShaderStageForValidation`), and use it as the source of truth for details of the stage being validated. This yields several immediate benefits, even before making adjustments for the new validation: - Stage-specific stage is now properly encapsulated. `compare_function`, which was previously passed as a `Option`al sibling argument, is now properly associated with only the vertex shader stage. - This led to an odd discovery that `compare_function` was being provided to `check_stages` with other stages, but not actually actually checked. This seems like a rightfully squashed bug. - Instead of passing a `wgpu_types::ShaderStages` (with a single bit) and `naga::ShaderStage` side-by-side, encapsulate both into conversion methods for an instance of `ShaderStageForValidation`, so errors are impossible to make.

…tion (minus `clip-distances`) Notable public API additions: - New `StageError` variants: - `VertexOutputLocationTooLarge` - `TooManyVertexOutputs` - Add new `shader_io_deductions` submodule of `wgpu_core::validation` with: - A `ShaderIoDeduction` trait - `enum MaxVertexShaderOutputDeduction` - `MaxInterStageShaderVariablesDeductions` for them.

…dation

…face::check_stage`

jimblandy changed the title ~~Finish migration from maxInterStageShaderComponents to maxInterStageShaderVariables`~~ Finish migration from maxInterStageShaderComponents to maxInterStageShaderVariables Dec 6, 2025

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch 6 times, most recently from b948e13 to 853e129 Compare December 18, 2025 19:06

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch from 853e129 to 3951f50 Compare December 19, 2025 06:13

ErichDonGubler changed the title ~~Finish migration from maxInterStageShaderComponents to maxInterStageShaderVariables~~ Add maxInterStageShaderVariables validation Dec 19, 2025

This was referenced Dec 19, 2025

Remove maxInterStageShaderComponents #8761

Closed

Add clip distances validation for maxInterStageShaderVariables #8762

Open

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch from 3951f50 to 32215a3 Compare December 19, 2025 18:47

ErichDonGubler changed the title ~~Add maxInterStageShaderVariables validation~~ Add maxInterStageShaderVariables validation (minus coverage of clip-distances) Dec 19, 2025

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch 2 times, most recently from 42456c9 to 3354ba5 Compare December 19, 2025 22:22

ErichDonGubler mentioned this pull request Dec 19, 2025

deno: Fix error reporting for async pipeline creation #8712

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6 tasks

ErichDonGubler changed the title ~~Add maxInterStageShaderVariables validation (minus coverage of clip-distances)~~ Migrate validation from maxInterStageShaderComponents to maxInterStageShaderVariables (minus coverage of clip-distances) Dec 19, 2025

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch 5 times, most recently from 6f1e549 to a9d5a27 Compare December 20, 2025 01:38

ErichDonGubler commented Dec 20, 2025

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ErichDonGubler force-pushed the max-inter-stage-shader-variables branch from a9d5a27 to 2c18228 Compare December 20, 2025 02:55

ErichDonGubler marked this pull request as ready for review December 22, 2025 19:27

ErichDonGubler assigned andyleiserson Dec 22, 2025

ErichDonGubler commented Dec 22, 2025

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ErichDonGubler force-pushed the max-inter-stage-shader-variables branch 4 times, most recently from 438f534 to 2ae309c Compare December 22, 2025 22:20

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…,maxInterStageShaderVariables:createRenderPipeline,at_over:… tests in CTS have issues outside a CI environment #8777

Open

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch from 2ae309c to 76bdf80 Compare December 22, 2025 22:33

andyleiserson approved these changes Dec 23, 2025

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ErichDonGubler added 2 commits December 23, 2025 15:00

refactor(core): make Interface::shader_stage_from_stage_bit a free …

b93a508

…function

refactor(core): reverse conv. b/w wgt::ShaderStages and `naga::Shad…

f3b5b5e

…erStage` This will better prepare for the subsequent commit, which supplants `naga::ShaderStage` as the source of truth in this code.

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch from 76bdf80 to d3eb071 Compare December 23, 2025 20:12

ErichDonGubler added a commit to erichdongubler-mozilla/wgpu that referenced this pull request Dec 23, 2025

docs(CHANGELOG): add entry for gfx-rs#8652

e0d67c8

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch from d3eb071 to 8694e44 Compare December 23, 2025 20:18

ErichDonGubler mentioned this pull request Dec 23, 2025

Add a lint for patterns for enum variants with no fields (unit variants) that don't need to use braces rust-lang/rust-clippy#16292

Closed

ErichDonGubler added 8 commits December 23, 2025 15:52

feat(core)!: add Limits::max_inter_stage_shader_variables

a0aaa0c

fix(core): add fragment-stage max_inter_stage_shader_variables vali…

49abc8c

…dation

fix(core): remove max_inter_stage_shader_components validation

b013b1d

docs(CHANGELOG): add entry for gfx-rs#8652

ff5d573

test(core): add CTS coverage for maxInterStageShaderVariables

6ecde40

docs(core): add (one among others) spec. citation for logic in `Inter…

83b6827

…face::check_stage`

ErichDonGubler force-pushed the max-inter-stage-shader-variables branch from 8694e44 to 83b6827 Compare December 23, 2025 20:55

ErichDonGubler mentioned this pull request Dec 23, 2025

Refactor 4 in <max inter-stage shader components> / 4 expressions in wgpu-hal to be a constant #8781

Open

ErichDonGubler merged commit a2c8c0d into gfx-rs:trunk Dec 23, 2025
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ErichDonGubler added a commit that referenced this pull request Dec 23, 2025

docs(CHANGELOG): add entry for #8652

ceb549b

ErichDonGubler deleted the max-inter-stage-shader-variables branch December 23, 2025 21:09

ErichDonGubler mentioned this pull request Dec 28, 2025

Remove SupportedLimits.maxInterStageShaderComponents #6290

Closed

2 tasks

	// Value supported by Intel Celeron B830 on Windows (OpenGL 3.1)
	// Intel Celeron B830 on Windows (OpenGL 3.1) supports up to 31 bytes (~8 variables)

Migrate validation from maxInterStageShaderComponents to maxInterStageShaderVariables (minus coverage of clip-distances) #8652

Migrate validation from maxInterStageShaderComponents to maxInterStageShaderVariables (minus coverage of clip-distances) #8652

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Migrate validation from `maxInterStageShaderComponents` to `maxInterStageShaderVariables` (minus coverage of `clip-distances`) #8652

Migrate validation from `maxInterStageShaderComponents` to `maxInterStageShaderVariables` (minus coverage of `clip-distances`) #8652

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