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wgsl: support swizzle assignment#5268

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dneto0 wants to merge 36 commits into
gpuweb:mainfrom
dneto0:swizzle-assignment
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wgsl: support swizzle assignment#5268
dneto0 wants to merge 36 commits into
gpuweb:mainfrom
dneto0:swizzle-assignment

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@dneto0

@dneto0 dneto0 commented Jul 28, 2025 •
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Add language extension 'swizzle_assignment'

Example:

var v:vec4u;
v.yz = vec2(1,2);

Issue: #737

@dneto0 dneto0 force-pushed the swizzle-assignment branch from fe9ba88 to d7c5282 Compare July 28, 2025 22:48
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github-actions Bot commented Jul 28, 2025 •
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Previews, as seen when this build job started (c55aadf):
WebGPU webgpu.idl | Explainer | Correspondence Reference
WGSL grammar.js | wgsl.lalr.txt

mehmetoguzderin
mehmetoguzderin reviewed Jul 28, 2025
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Comment thread wgsl/syntax.bnf
@dneto0 dneto0 force-pushed the swizzle-assignment branch from d7c5282 to c984105 Compare July 29, 2025 14:26
@dneto0 dneto0 added this to the Milestone 3+ milestone Jul 29, 2025
@dneto0 dneto0 force-pushed the swizzle-assignment branch 2 times, most recently from abeafa1 to 9aa6e7f Compare July 29, 2025 14:55
@Kangz

Kangz commented Aug 19, 2025

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GPU Web WG 2025-07-30 Atlantic-time
  • (Revised)
  • DN: people have wanted swizzle assignment for a long time. We can give them what they want. Can show them what will work and what won't.
  • DN: subtle: order of operations in e.g. compound assignment. Eval of RHS can modify memory you're evaluating on the LHS. Have already spoken with Oguz and Alan about it.
    • JP: This happens today in assignment to component of a vector.

@stefnotch stefnotch mentioned this pull request Sep 8, 2025
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dj2
dj2 reviewed Oct 2, 2025
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Comment thread wgsl/index.bs Outdated
@mwyrzykowski mwyrzykowski self-requested a review October 2, 2025 15:12
dneto0
dneto0 commented Oct 24, 2025
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There is an interaction with 15.2.5 Function Scope Variable Value Analysis, where a swizzle view should sometimes be considered a full reference. It would be if the root variable is of vector type, because a swizzle assignment is deemed to be overwriting the entire vector.

@jimblandy

jimblandy commented Nov 3, 2025

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@dneto0 I gather that, since this is a draft, it's not ready for committee discussion?

@stefnotch stefnotch mentioned this pull request Nov 24, 2025
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@dneto0 dneto0 force-pushed the swizzle-assignment branch from f17717e to 57f69a1 Compare January 6, 2026 20:21
@jimblandy jimblandy added this to WGSL Jan 12, 2026
@jimblandy jimblandy moved this to Future agenda in WGSL Jan 12, 2026
copybara-service Bot pushed a commit to google/dawn that referenced this pull request Jan 22, 2026
@sudonatalie
[Tint] Add Swizzle View type
f38fc0d 
Add a new core type called Swizzle View that is used as the type of
swizzle expressions in the resolver. This change is based on the draft
spec in: gpuweb/gpuweb#5268

Currently, there should be no functional change, it simply changes the
sem node types, which are then lowered in ProgramToIR to the expected
vector types. However, this change supports a future implementation of
swizzle assignment, where it will be necessary for swizzled objects to
be treated as memory views rather than concrete values.

Bug: 473857629
Change-Id: I34342f921e6906b599f840c10dbb455eed37cb94
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/285675
Reviewed-by: dan sinclair <[email protected]>
Commit-Queue: Natalie Chouinard <[email protected]>
Reviewed-by: James Price <[email protected]>
@dneto0

dneto0 commented Feb 3, 2026

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@dneto0 I gather that, since this is a draft, it's not ready for committee discussion?

That's correct. We're implementing a prototype. We'll come back to committee when we are confident in the spec and tests. Also I haven't addressed Alan's feedback on the spec-writing aspect of it.

@jimblandy jimblandy moved this from Future agenda to Awaiting investigation / implementation in WGSL Feb 9, 2026
copybara-service Bot pushed a commit to google/dawn that referenced this pull request Feb 19, 2026
@sudonatalie
[tint] Add support for swizzle assignment
bb10f60 
Add WGSL language support for swizzle assignment on vectors as a proof
of concept. This implementation is based on the draft spec and passes
all CTS tests. It is enabled behind the swizzle_assignment language
feature flag as an unsafe experimental feature.

Draft Spec: gpuweb/gpuweb#5268

Bug: 473857629
Change-Id: Ic111554c53e41a9f3305f3118258f7dd5df4a29d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/290357
Commit-Queue: Natalie Chouinard <[email protected]>
Reviewed-by: dan sinclair <[email protected]>
@dneto0 dneto0 force-pushed the swizzle-assignment branch 2 times, most recently from 32ce5fc to 9a0cd0e Compare February 26, 2026 22:16
@dneto0

dneto0 commented Feb 26, 2026

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The latest patches from today include a fix for the order of evaluation, and includes two worked examples: one for assignment, another for compound assignment.

@dneto0 dneto0 requested a review from sudonatalie February 26, 2026 22:18
@dneto0

dneto0 commented Feb 26, 2026

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index.html

Attaching rendered HTML

sudonatalie
sudonatalie reviewed Feb 27, 2026
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Comment thread wgsl/index.bs Outdated
Comment thread wgsl/index.bs Outdated
@dneto0

dneto0 commented Feb 27, 2026

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updated index.html

@dneto0 dneto0 requested a review from sudonatalie February 27, 2026 23:45
dneto0 added 25 commits June 5, 2026 16:31
@dneto0
Describe originating variable of reference-from-swizzle view via single
b24c0f0 
letter.
@dneto0
Table for swizzle view from memory view: add condition on swizzle_ass…
8d7c739 
…ignment
@dneto0
Define full/partial swizzle view and update uniformity statement rules
63ac7c5
@dneto0
Tighten wording in component reference from Vector Memory View or Swi…
d8c27ec 
…zzle View

The result is always a reference, not just a memory view.
@dneto0
better linking
ca79b3f
@dneto0
Reads and Writes happen during swizzle assignment
e3fdcbd
@dneto0
Fix unenclosed </div>
1756726
@dneto0
Remove stray .python-version
1fe4680
@dneto0
Add the swizzle case to LHSValue unfiormity rules
d3cf002
@dneto0
Delete stray .python-version file
2ec9bc7
@dneto0
editorial: Link the "Swizzle Assignment" section to the language exte…
d541b64 
…nsion
@dneto0
Explain the interaction of SwizzleViewWrite with uniformity and the m…
2585cad 
…emory model
@dneto0
delete parameter list from "Algorithm: SwizzleViewWrite"
e66e07b 
That makes it consistent with other "Algorithm" blocks.
@dneto0
swizzle view access mode must be read or read_write
81ccc2b 
SwizzleViewWrite is only usable with read_write swizzle views
@dneto0
Use W3C "list" notation instead of making up index sequence
19b41d6 
Also, rename IndexSeq to IndexList
@dneto0
Assert IndexList has InputK items.
36a3dd7 
This is in the "swizzle view from swizzle view" table.
@dneto0
Elaborate steps in compound assignment via reference
206d013 
This gives it structure parallel to compound assignment via swizzle
view, so they are easier to compare.
It removes a possibly-confusing reference to using the load rule.
@dneto0
Indent as needed in Load Rule and Swizzle View Load Rule
7c36673
@dneto0
Rewrite comment about applying single letter to swizzle view
de52d95
@dneto0
Fix comment about assigning to swizzle with repeated components
b76c191
@dneto0
Elaborated comment in "invalid swizzle views" example
25bfb08
@dneto0
Add note that swizzle view types are not spelled out in WGSL source
735e8f8
@dneto0
Add swizzle view cases to "use cases for references and pointers"
fca0cc7
@dneto0
add missing parallel cases to memory-view, outside of the memory mode…
f7d0588 
…l section
@dneto0
add missing parallel cases to memory-view: memory model section
c55aadf
@dneto0 dneto0 force-pushed the swizzle-assignment branch from 17026de to c55aadf Compare June 5, 2026 20:31
@dneto0

dneto0 commented Jun 5, 2026

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For @alan-baker, two substantively reviewable changes:

  • swizzle view types are only defined when access mode is read or read_write
  • memory model:
    • restated rules about what memory locations are touched by a memory access: pull the "write to vector component" into the main part of the text, instead of as a note.
    • memory model section says what locations are touched by an operation occurring via swizzle-view.

@dneto0

dneto0 commented Jun 5, 2026

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ok @jimblandy I have addressed all comments so far. Please mark your comments are "resolved" when you are happy that the changes are satisfactory. I've resolved a few of the more trivial cases.

@alan-baker alan-baker modified the milestones: Milestone 4+, Milestone 2 Jun 7, 2026
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@sudonatalie sudonatalie sudonatalie approved these changes

@mehmetoguzderin mehmetoguzderin mehmetoguzderin approved these changes

@alan-baker alan-baker alan-baker approved these changes

@mwyrzykowski mwyrzykowski mwyrzykowski approved these changes

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@dneto0 @Kangz @jimblandy @alan-baker @kainino0x @dj2 @sudonatalie @mehmetoguzderin @mwyrzykowski