Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 0f12e79a9bd41fdb635555d0a08db893d4670801
https://github.com/WebKit/WebKit/commit/0f12e79a9bd41fdb635555d0a08db893d4670801
Author: Tadeu Zagallo <[email protected]>
Date: 2023-06-05 (Mon, 05 Jun 2023)
Changed paths:
M Source/WebGPU/WGSL/AST/ASTStructure.h
M Source/WebGPU/WGSL/GlobalVariableRewriter.cpp
M Source/WebGPU/WGSL/Metal/MetalFunctionWriter.cpp
A Source/WebGPU/WGSL/tests/valid/packing.wgsl
Log Message:
-----------
[WGSL] Don't pack user-defined structs
https://bugs.webkit.org/show_bug.cgi?id=257653
rdar://110175536
Reviewed by Myles C. Maxfield.
WGSL distinguishes from Metal in the representation of `vec3`. In WGSL, the size
of `vec3<T>` is `3 * sizeof(T)` and the alignment is `4 * sizeof(T)`. In Metal,
we translate `vec3<T>` to `vec<T, 3>`, which has both size and alignment equal
to `4 * sizeof(T)`. This difference is observable through buffers.
The implementation to pack structs was first introduced in 264243@main, by using
packed types (e.g. `packed_float3`). Originally, all structs were packed, but
packed types aren't allowed everywhere, for example on the vertex output. To fix
that, in 264277@main, I changed it so that we only pack user-defined structs,
but
that is not correct either, since not all operations work on packed types. An
example is matrix multiplication: we can only multiply a matrix by `vec<float,
3>`,
not `packed_float3`.
To implement this correctly, we need to distinguish between a packed and
unpacked
struct, and we can't modify the original struct. Packed structs are only
necessary
for resources, and in that case we need to create a duplicate, packed version
of the
struct. This is the first of a series of patches that implement the proper
behavior.
For now, we merely set up the duplicate struct and introduce 2 new struct roles
to
give us more information about packed structs. This information will be used in
the
following patches to determine where we need to explicitly pack and upack
values.
* Source/WebGPU/WGSL/AST/ASTStructure.h:
* Source/WebGPU/WGSL/GlobalVariableRewriter.cpp:
(WGSL::RewriteGlobalVariables::collectGlobals):
(WGSL::RewriteGlobalVariables::packResourceStruct):
* Source/WebGPU/WGSL/Metal/MetalFunctionWriter.cpp:
(WGSL::Metal::FunctionDefinitionWriter::visit):
* Source/WebGPU/WGSL/tests/valid/packing.wgsl: Added.
Canonical link: https://commits.webkit.org/264864@main
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