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Clarify that evaluations to inf/nan may yield undef value - #2777

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kdashg merged 1 commit into
gpuweb:mainfrom
dneto0:issue-2776
May 31, 2022
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Clarify that evaluations to inf/nan may yield undef value#2777
kdashg merged 1 commit into
gpuweb:mainfrom
dneto0:issue-2776

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@dneto0

@dneto0 dneto0 commented Apr 20, 2022

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Fixes: #2776

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dneto0 requested a review from alan-baker April 20, 2022 17:36
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dneto0 commented Apr 20, 2022

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I'm not sure if this is the best way to say it. Feedback desired.

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github-actions Bot commented Apr 20, 2022

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Previews, as seen when this build job started (03bf6a2):
WebGPU | IDL
WGSL
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@kdashg

kdashg commented Apr 26, 2022

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We we want to split hairs here and go with "implementation-defined"? Is that even accurate?

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kdashg commented Apr 26, 2022

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WGSL meeting minutes 2022-04-26
  • AB: We should probably use the same language as e.g. OOB access.
  • BC: Concern with “impl defined” implies a consistent behavior, and we don’t have that.
  • MM: What is the granularity of this? E.g. can multiple runs have different results? Are results different within the same execution?
  • MM: “The value of an undefined value would not change from one line to the next” such that we don’t get e.g. undefined branchin.
  • JB: THis is something a user wants to know. Like “can I dupe this expr and have it have the same result”.
  • AB: I agree that this sounds useful but I’m not sure how I (or MM?) would implement it?
  • MM:
  • AB: I know how I’d do it in llvm, but not sure about it other backends.
  • MM: One solution: “For each expression that can produce UV, I will produce a value”, but if you want to rely on what spir-v has, I’m not sure what spir-v can guarantee w.r.t. UVs.
  • AB: I wouldn’t want to have to insert e.g. clamping code after every UV application. I would like to distinguish between cases where we can guarantee it, vs cases where the underlying system has UV issues.
  • MM: Less concerned about the portability than the ability for an author to get reasonable logical execution. E.g. skipping branches.
  • BC: Not sure if it’s possible to do better.
  • KG: Can we call it “arbitrary value”? Then we can rely on normal logical flow.
  • MM: Yes that’s cool what I’m asking for.
  • BC: Still not sure it’s implementable.
  • KG: Can you give us examples where even branches wouldn’t be able to safely give us arbitrary values?
  • BC: Yes I’ll find them.

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kdashg commented May 13, 2022

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I think I want to discuss #2888 first.

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kdashg commented May 31, 2022

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WGSL meeting minutes 2022-05-31
  • KG: Wanted to discuss undef value first, but don’t care anymore. Lets land if that’s tolerable and fixup afterwards. Can either land what we mean and then fix, or land better language and use here. Either order is fine with me.
  • DN: Either is fine with me. This is a net improvement.
  • KG: Let’s take this.

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kdashg merged commit 382565f into gpuweb:main May 31, 2022
github-actions Bot added a commit that referenced this pull request May 31, 2022
@dneto0 @github-actions
Clarify that evaluations to inf/nan may yield undef value (#2777)
1006802 
SHA: 382565f
Reason: push, by @kdashg

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
github-actions Bot added a commit that referenced this pull request May 31, 2022
@dneto0 @github-actions
Clarify that evaluations to inf/nan may yield undef value (#2777)
f3eb1da 
SHA: 382565f
Reason: push, by @kdashg

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
github-actions Bot added a commit that referenced this pull request May 31, 2022
@dneto0 @github-actions
Clarify that evaluations to inf/nan may yield undef value (#2777)
a90ea2c 
SHA: 382565f
Reason: push, by @kdashg

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
jdarpinian pushed a commit to jdarpinian/gpuweb that referenced this pull request Aug 12, 2022
@dneto0 @jdarpinian
Clarify that evaluations to inf/nan may yield undef value (gpuweb#2777)
2f0985f 
Fixes: gpuweb#2776
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@kdashg kdashg kdashg approved these changes
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wgsl: clarify that when inf/nan are not supported, that such evaluations produced undefined value of the given type

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