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521e98405f
* Update release number to 120.
Github Issues:
* Add slink:VkAccelerationStructureTypeNV explicitly to extension XML for
`<<VK_NV_ray_tracing>>` (public issue 848).
* Add missing valid usage statements for feature flags in
slink:VkCommandBufferInheritanceInfo (public pull request 1017).
Internal Issues:
* Clarify behavior of non-premultiplied destination colors for
`<<VK_EXT_blend_operation_advanced>>` prior to the definition of
slink:VkBlendOverlapEXT (internal issue 1766).
* Fix the confusing phrasing "`no other queue must: be (doing something)`"
for flink:vkQueuePresentKHR, flink:vkQueueSubmit, and
flink:vkQueueBindSparse (internal issue 1774).
* Add `<<VK_EXT_validation_features>>` flag to enable best practices
checks, which will soon be available in the validation layer (internal
issue 1779).
* Specify allowed characters for VUID tag name components in the style
guide (internal issue 1788).
* Update links to SPIR-V extension specifications, and parameterize their
markup in case the URLs change in the future (internal issue 1797).
* Fix an off-by-one error in the valid usage statement for
slink:VkPipelineExecutableInfoKHR (internal merge request 3303).
* Clean up markup indentation not matching the style guide (internal merge
request 3314).
* Minor script updates to allow refpage aliases, generate a dynamic TOC
for refpages, generate Apache rewrite rules for aliases, open external
links from refpages in a new window, and synchronize with the OpenCL
scripts. This will shortly enable a paned navigation setup for refpages,
similar to the OpenCL 2.2 refpages (internal merge request 3322).
* Script updates to add tests to the checker, refactor and reformat code,
generate better text for some valid usage statements, use more Pythonic
idioms, and synchronize with the OpenXR scripts (internal merge request
3239).
* Script updates and minor fixes in spec language to not raise checker
errors for refpage markup of pages not existing in the API, such as
VKAPI_NO_STDINT_H. Remove corresponding suppression of some
check_spec_links.py tests from .gitlab-ci.yml and 'allchecks' target
(internal merge request 3315).
133 lines
4.0 KiB
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133 lines
4.0 KiB
Plaintext
include::meta/VK_EXT_shader_subgroup_vote.txt[]
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*Last Modified Date*::
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2016-11-28
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*IP Status*::
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No known IP claims.
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*Interactions and External Dependencies*::
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- This extension requires the
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{spirv}/KHR/SPV_KHR_subgroup_vote.html[`SPV_KHR_subgroup_vote`] SPIR-V
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extension.
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- This extension requires the
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https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_shader_group_vote.txt[`GL_ARB_shader_group_vote`]
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extension for GLSL source languages.
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*Contributors*::
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- Neil Henning, Codeplay
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- Daniel Koch, NVIDIA Corporation
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This extension adds support for the following SPIR-V extension in Vulkan:
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* `SPV_KHR_subgroup_vote`
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This extension provides new SPIR-V instructions:
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* code:OpSubgroupAllKHR,
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* code:OpSubgroupAnyKHR, and
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* code:OpSubgroupAllEqualKHR.
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to compute the composite of a set of boolean conditions across a group of
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shader invocations that are running concurrently (a _subgroup_).
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These composite results may be used to execute shaders more efficiently on a
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slink:VkPhysicalDevice.
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When using GLSL source-based shader languages, the following shader
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functions from GL_ARB_shader_group_vote can map to these SPIR-V
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instructions:
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* code:anyInvocationARB() -> code:OpSubgroupAnyKHR,
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* code:allInvocationsARB() -> code:OpSubgroupAllKHR, and
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* code:allInvocationsEqualARB() -> code:OpSubgroupAllEqualKHR.
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The subgroup across which the boolean conditions are evaluated is
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implementation-dependent, and this extension provides no guarantee over how
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individual shader invocations are assigned to subgroups.
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In particular, a subgroup has no necessary relationship with the compute
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shader _local workgroup_ -- any pair of shader invocations in a compute
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local workgroup may execute in different subgroups as used by these
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instructions.
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Compute shaders operate on an explicitly specified group of threads (a local
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workgroup), but many implementations will also group non-compute shader
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invocations and execute them concurrently.
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When executing code like
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[source,c++]
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----------------------------------------
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if (condition) {
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result = do_fast_path();
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} else {
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result = do_general_path();
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}
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----------------------------------------
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where code:condition diverges between invocations, an implementation might
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first execute code:do_fast_path() for the invocations where code:condition
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is true and leave the other invocations dormant.
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Once code:do_fast_path() returns, it might call code:do_general_path() for
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invocations where code:condition is code:false and leave the other
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invocations dormant.
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In this case, the shader executes *both* the fast and the general path and
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might be better off just using the general path for all invocations.
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This extension provides the ability to avoid divergent execution by
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evaluating a condition across an entire subgroup using code like:
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[source,c++]
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----------------------------------------
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if (allInvocationsARB(condition)) {
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result = do_fast_path();
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} else {
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result = do_general_path();
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}
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----------------------------------------
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The built-in function code:allInvocationsARB() will return the same value
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for all invocations in the group, so the group will either execute
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code:do_fast_path() or code:do_general_path(), but never both.
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For example, shader code might want to evaluate a complex function
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iteratively by starting with an approximation of the result and then
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refining the approximation.
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Some input values may require a small number of iterations to generate an
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accurate result (code:do_fast_path) while others require a larger number
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(code:do_general_path).
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In another example, shader code might want to evaluate a complex function
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(code:do_general_path) that can be greatly simplified when assuming a
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specific value for one of its inputs (code:do_fast_path).
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=== New Object Types
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None.
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=== New Enum Constants
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None.
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=== New Enums
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None.
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=== New Structures
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None.
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=== New Functions
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None.
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=== New Built-In Variables
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None.
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=== New SPIR-V Capabilities
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* <<spirvenv-capabilities-table-subgroupvote,SubgroupVoteKHR>>
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=== Issues
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None.
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=== Version History
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* Revision 1, 2016-11-28 (Daniel Koch)
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- Initial draft
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