commit 6ee5b8fed80589de02b551fbc2e52eb9dde91f89
author Antonio Maiorano <amaiorano@google.com> Tue Oct 28 17:47:17 2025 -0700
committer Dawn LUCI CQ <dawn-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Oct 28 17:47:17 2025 -0700
tree bc85793f9ffbf87cbf8bab6095117a9d2573af01
parent b2e93484bc0611525df54473e6771ad3e4500c6d

d3d12: optimize root signature slot usage for dynamic storage buffers

Rather than bind dynamic storage buffers to root descriptors as [base
offset + dynamic offset, size], bind them instead to the root descriptor
table at [base offset, full size - base offset], and store the dynamic
offset as a root constant. The dynamic offsets are fed to Tint via
ArrayOffsetFromUniform, and thus are applied at shader runtime by
reading the offsets from a UBO and adding them to all reads/writes of
dynamic storage buffers.

Before this change, each dynamic storage buffer binding would use 3 root
signature slots: 2 for the root descriptor binding, and 1 for the buffer
length. With this change, each binding now takes 2 root signature slots:
1 for the buffer length (as before), and 1 for the buffer offset. This
frees up 8 slots (maxDynamicStorageBuffersPerPipelineLayout) in total.

Other things to point out:

- Added BindGroupTests.DynamicOffsetsWithAtomicOperations test to cover
  the case of atomic operations on dynamic buffers. This is because
  along with (RW)ByteAddressBuffer Load and Store functions, the
  Interlocked* functions are the ones that take an offset, so we want to
  make sure the dynamic offsets are properly applied.
- Added some useful comments to DynamicBufferOffsetTests.
- Added dawn::ityp::stack_vec::empty()
- Added dawn::ityp::vector::resize(Index, const Value&) overload

Bug: 449703736
Change-Id: I394ae0a82352eda9b8d109fabf05597339fd4d47
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/267454
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Loko Kung <lokokung@google.com>
Reviewed-by: Jiawei Shao <jiawei.shao@intel.com>