Erase explicit layout decorations (`Offset`/`ArrayStride`) when disallowed by Vulkan. #379

eddyb · 2025-09-08T12:29:47Z

More recent Vulkan SDK versions have started complaining about types having explicit memory layout, when used with memory that doesn't inherently require explicit layouts (only push constants and buffers really do), e.g.:

error: line 1097: [VUID-StandaloneSpirv-None-10684] Invalid explicit layout decorations on type for operand '367[%_ptr_Function__struct_61]'
  %1207 = OpVariable %_ptr_Function__struct_61 Function

The solution used here is simpler and more specialized (a pass that erases the explicit layout decorations from types behind pointers in storage classes that don't support them, combined with updating affected loads/stores) than what I originally described in #266 (comment), so we can hopefully use this for now and not worry about spirt::{mem,qptr} for the next release.

fixes spirv-tools v2025.2 makes compiletest fail #276
fixes Workgroup doesn't work in MoltenVk #266
(not actually tested with MoltenVK, we should make sure it actually works now)
see also spirv-val over-validation on private variable decoration KhronosGroup/SPIRV-Tools#6193

.github/workflows/ci.yaml

Firestar99 · 2025-09-18T20:59:21Z

I just want to note that you're upgrading CI's Vulkan SDK to 1.4.321.0, but use-compiled-tools is still on 1.4.309.0, so we could have a scenario where the old SDK fails where the new SDK passes. I know that upgrading spirv-tools isn't trivial this time, so I would let this pass as is, just something to be aware of.

eddyb · 2025-09-19T04:53:46Z

TODO: before landing this, we should update spirv-tools-rs as well (I only changed the Vulkan SDK version that is used for CI, via the use-installed-tools feature).

@Firestar99 I 100% agree, that's why I still have the above quoted bit in the PR description, and it's why this PR was in draft state even before rebasing it on top of #400 (I know it'd be slower but it'd be nice to test use-compiled-tools as well, not just use-installed-tools, in CI).

EDIT: fixed the spirv-tools-rs upgrade and landed it:

update vulkan-sdk-1.4.321 spirv-tools-rs#19

eddyb · 2025-09-19T07:19:58Z

As the spirv-tools-rs update PR was merged:

update vulkan-sdk-1.4.321 spirv-tools-rs#19

I was able to get 10 failures in cargo compiletest by using it and turning off the new pass:

diff --git a/Cargo.toml b/Cargo.toml
index 7cf09984100..9da910407c9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -49,3 +49,3 @@ spirv-std-types = { path = "./crates/spirv-std/shared", version = "=0.9.0" }
 spirv-std-macros = { path = "./crates/spirv-std/macros", version = "=0.9.0" }
-spirv-tools = { version = "0.12.1", default-features = false }
+spirv-tools = { version = "0.12.1", git = "https://github.com/Rust-GPU/spirv-tools-rs", default-features = false }
 rustc_codegen_spirv = { path = "./crates/rustc_codegen_spirv", version = "=0.9.0", default-features = false }
diff --git a/crates/rustc_codegen_spirv/src/linker/mod.rs b/crates/rustc_codegen_spirv/src/linker/mod.rs
index d289c8e5fce..89c46e11f03 100644
--- a/crates/rustc_codegen_spirv/src/linker/mod.rs
+++ b/crates/rustc_codegen_spirv/src/linker/mod.rs
@@ -564,3 +564,3 @@ pub fn link(
 
-        {
+        if false {
             let timer = before_pass("spirt_passes::explicit_layout::erase_when_invalid");

Re-enabling the pass (removing if false), while keeping the newer spirv-tools-rs, passes cargo compiletest.

So we should be able to land this once we release another version of spirv-tools-rs, AIUI.

Firestar99 · 2025-09-23T13:38:08Z

Should I release spirv-tools for you?

eddyb · 2025-09-24T14:38:47Z

Should I release spirv-tools for you?

Yes, that would be great, thanks!
_{(sorry for not being clearer - and also missing the notif for this - alternatively I could handle the release if it's easier for you, but I was worrying of subtleties around that specific project, I don't think we have a very unified flow yet across repos)}

Firestar99 · 2025-10-02T17:10:48Z

(welp and I completely missed your message)

Anyway, I thought I'd give spirv-tools some love before we release:

Afterwards, a release should just be a trivial cargo release minor in the root workspace

…lowed by Vulkan.

eddyb · 2025-10-07T09:47:21Z

🎯 [Cache] Restored Vulkan SDK in path: '/home/runner/vulkan-sdk'. Cache Restore ID: 'cache-linux-x64-vulkan-sdk-1.4.309.0'.
Warning: Vulkan SDK path doesn't exist: /home/runner/vulkan-sdk/1.4.321.0/x86_64
Warning: Could not find Vulkan SDK in /home/runner/vulkan-sdk/1.4.321.0/x86_64

This is very confusing. It doesn't seem to actually ignore the cache if it's the wrong version. Not sure why only Linux seems to be affected. Will purge GHA caches for old version and see what happens.

Firestar99

I feel like I can't really comment too much on the code, as I'm totally unfamiliar with spirt. I should probably start reading into the library a bit at some point, since I assume most of our current passes will eventually end up in spirt anyway.

Firestar99 · 2025-10-07T11:15:47Z

crates/rustc_codegen_spirv/src/linker/spirt_passes/explicit_layout.rs

+        let wk = self.wk;
+
+        // FIXME(eddyb) this might need to include `Workgroup`, specifically when
+        // `WorkgroupMemoryExplicitLayoutKHR` is being relied upon.


Shouldn't Workgroup be in this list, as #266 shows the declarations need to be removed? I'd be fine not supporting WorkgroupMemoryExplicitLayoutKHR for the moment, haven't heard of the extension myself nor anyone using it. If somebody wants support, we can always add it later.

VK extension: https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#VK_KHR_workgroup_memory_explicit_layout

Coverage 25.68% 74.32% is quite good

The list is for the storage classes that allow and/or require the "explicit layout" (Offset/ArrayStride) decorations.

So everything missing here (like Function, Private, Workgroup, or weird storage classes used only within raytracing pipelines etc.) will have the decorations removed.

Maybe it's a bit confusing that the calls to this method look like:

!self.addr_space_allows_explicit_layout(...)

But it's fundamentally a small set of storage classes for which the decoderations are allowed:

This chapter describes valid uses for a set of SPIR-V decorations. Any other use of one of these decorations is invalid,

(from https://docs.vulkan.org/spec/latest/chapters/interfaces.html - Ctrl+F ArrayStride on that page to find all the instances where they explicitly allow - or rather, require - explicit layout)

Firestar99 · 2025-10-07T11:18:53Z

crates/rustc_codegen_spirv/src/linker/spirt_passes/explicit_layout.rs

+        }
+    }
+
+    fn in_place_transform_global_var_decl(&mut self, gv_decl: &mut GlobalVarDecl) {


spirt question: I don't fully understand why some visitor functions are *_in_place and others are not and returned Transformed<T> instead

It's a combination of 2-3 things:

wanting Transformed's distinction of whether a chance is actually needed, to bypass work
(but that requires by-value returns to avoid misuse)

anything interned (AttrSet/Const/Type) can't do in-place mutation
(so they use &FooDef -> Transformed<FooDef> + only re-interning when changed)

module-owned entities (GlobalVar/Func and intra-func regions/nodes) can do in-place mutation
(and cloning the whole definition to return it via Transformed would be prohibitively expensive)

Firestar99 · 2025-10-07T11:21:01Z

crates/rustc_codegen_spirv/src/linker/spirt_passes/explicit_layout.rs

+                    assert_eq!(sc_kind, wk.StorageClass);
+                    !self.addr_space_allows_explicit_layout(AddrSpace::SpvStorageClass(sc))
+                }
+                _ => unreachable!(),


spirt question: I also have no idea if this unreachable is actually unreachable, or how exactly imms and type_and_const_inputs works, since they're unfortunately not documented.

A SPIR-V "immediate" (in the spirt::spv::Imm sense) is similar to rspirv::dr::Operand w/o the Id variants (as SPIR-V IDs always correspond to some Type/Const/GlobalVar/Func/etc. interned/owned entity in SPIR-T - in the case of types, type_and_const_inputs lets them refer to other Types and/or Consts, through SPIR-V IDs, but nothing else).

So hitting this unreachable!() would require interning a type with a spirt::TypeKind::SpvInst that:

couldn't naturally be produced by SPIR-V -> SPIR-T (spirt::spv::lower)

would fail SPIR-T -> SPIR-V (spirt::spv::lift)

might error/panic in other parts of SPIR-T (that e.g. decode a spv::Inst's spv::Imms according to the SPIR-V "grammar")

eddyb · 2025-10-07T16:00:18Z

crates/rustc_codegen_spirv/src/linker/spirt_passes/explicit_layout.rs

+                    let is_explicit_layout_decoration = match attr {
+                        Attr::SpvAnnotation(attr_spv_inst)
+                            if (attr_spv_inst.opcode == wk.OpDecorate
+                                && [wk.ArrayStride, wk.MatrixStride]


Oh, phew, I was worried this only mentioned ArrayStride, but I did include MatrixStride just in case (I guess the one instance of non-explicit-layout matrices would have to bein the context of raytracing pipelines - e.g. Ctrl+F "matrix" on https://github.khronos.org/SPIRV-Registry/extensions/KHR/SPV_KHR_ray_tracing.html - though an even simpler example is just a local variable containing a matrix).

eddyb requested review from LegNeato, Firestar99 and schell as code owners September 8, 2025 12:29

eddyb marked this pull request as draft September 8, 2025 12:30

eddyb force-pushed the erase-explicit-layout-sometimes-maybe branch 3 times, most recently from 0fd77cb to 707bdcc Compare September 9, 2025 08:45

eddyb commented Sep 10, 2025

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eddyb mentioned this pull request Sep 18, 2025

ci: switch to jakoch/install-vulkan-sdk-action@v1 for Vulkan SDK + SwiftShader. #400

Merged

eddyb force-pushed the erase-explicit-layout-sometimes-maybe branch from 8d01e85 to 84ed68f Compare September 18, 2025 16:49

eddyb force-pushed the erase-explicit-layout-sometimes-maybe branch from 84ed68f to 5a77372 Compare September 19, 2025 06:53

Firestar99 mentioned this pull request Oct 7, 2025

spirv-tools: update to 0.13.0 #426

Closed

eddyb and others added 3 commits October 7, 2025 11:48

Erase explicit layout decorations (Offset/ArrayStride) when disal…

ab7b810

…lowed by Vulkan.

ci: update Vulkan SDK to 1.4.321.0.

c49a141

spirv-tools: update to 0.13.0

9b425ac

eddyb force-pushed the erase-explicit-layout-sometimes-maybe branch from 5a77372 to 9b425ac Compare October 7, 2025 08:49

eddyb marked this pull request as ready for review October 7, 2025 08:49

eddyb enabled auto-merge October 7, 2025 08:50

Firestar99 reviewed Oct 7, 2025

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eddyb commented Oct 7, 2025

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Erase explicit layout decorations (Offset/ArrayStride) when disallowed by Vulkan. #379

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Erase explicit layout decorations (Offset/ArrayStride) when disallowed by Vulkan. #379

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Erase explicit layout decorations (`Offset`/`ArrayStride`) when disallowed by Vulkan. #379

Erase explicit layout decorations (`Offset`/`ArrayStride`) when disallowed by Vulkan. #379

eddyb commented Sep 8, 2025 •

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