Deprecation state
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Promoted to Vulkan 1.2
Contact
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Alexander Galazin alegal-arm
Other Extension Metadata
- Last Modified Date
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2018-09-11
- Interactions and External Dependencies
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Promoted to Vulkan 1.2 Core
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This extension requires
SPV_KHR_float_controls
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- IP Status
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No known IP claims.
- Contributors
-
-
Alexander Galazin, Arm
-
Jan-Harald Fredriksen, Arm
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Jeff Bolz, NVIDIA
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Graeme Leese, Broadcom
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Daniel Rakos, AMD
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Description
The VK_KHR_shader_float_controls
extension enables efficient use of
floating-point computations through the ability to query and override the
implementation’s default behavior for rounding modes, denormals, signed
zero, and infinity.
Promotion to Vulkan 1.2
All functionality in this extension is included in core Vulkan 1.2, with the KHR suffix omitted. The original type, enum and command names are still available as aliases of the core functionality.
New Enum Constants
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VK_KHR_SHADER_FLOAT_CONTROLS_EXTENSION_NAME
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VK_KHR_SHADER_FLOAT_CONTROLS_SPEC_VERSION
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Extending VkShaderFloatControlsIndependence:
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VK_SHADER_FLOAT_CONTROLS_INDEPENDENCE_32_BIT_ONLY_KHR
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VK_SHADER_FLOAT_CONTROLS_INDEPENDENCE_ALL_KHR
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VK_SHADER_FLOAT_CONTROLS_INDEPENDENCE_NONE_KHR
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Extending VkStructureType:
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VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FLOAT_CONTROLS_PROPERTIES_KHR
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Issues
1) Which instructions must flush denorms?
RESOLVED: Only floating-point conversion, floating-point arithmetic,
floating-point relational (except OpIsNaN
, OpIsInf
), and
floating-point GLSL.std.450 extended instructions must flush denormals.
2) What is the denorm behavior for intermediate results?
RESOLVED: When a SPIR-V instruction is implemented as a sequence of other instructions:
-
in the
DenormFlushToZero
execution mode, the intermediate instructions may flush denormals, the final result of the sequence must not be denormal. -
in the
DenormPreserve
execution mode, denormals must be preserved throughout the whole sequence.
3) Do denorm and rounding mode controls apply to OpSpecConstantOp
?
RESOLVED: Yes, except when the opcode is OpQuantizeToF16
.
4) The SPIR-V specification says that OpConvertFToU
and
OpConvertFToS
unconditionally round towards zero.
Do the rounding mode controls specified through the execution modes apply to
them?
RESOLVED: No, these instructions unconditionally round towards zero.
5) Do any of the “Pack” GLSL.std.450 instructions count as conversion instructions and have the rounding mode applied?
RESOLVED: No, only instructions listed in “section 3.32.11. Conversion Instructions” of the SPIR-V specification count as conversion instructions.
6) When using inf/nan-ignore mode, what is expected of OpIsNan
and
OpIsInf
?
RESOLVED: These instructions must always accurately detect inf/nan if it is passed to them.
Version 4 API incompatibility
The original versions of VK_KHR_shader_float_controls
shipped with
booleans named “separateDenormSettings” and
“separateRoundingModeSettings”, which at first glance could have indicated
“they can all be set independently, or not”.
However the spec language as written indicated that the 32-bit value could
always be set independently, and only the 16- and 64-bit controls needed to
be the same if these values were VK_FALSE
.
As a result of this slight disparity, and lack of test coverage for this facet of the extension, we ended up with two different behaviors in the wild, where some implementations worked as written, and others worked based on the naming. As these are hard limits in hardware with reasons for exposure as written, it was not possible to standardise on a single way to make this work within the existing API.
No known users of this part of the extension exist in the wild, and as such the Vulkan WG took the unusual step of retroactively changing the once boolean value into a tri-state enum, breaking source compatibility. This was however done in such a way as to retain ABI compatibility, in case any code using this did exist; with the numerical values 0 and 1 retaining their original specified meaning, and a new value signifying the additional “all need to be set together” state. If any applications exist today, compiled binaries will continue to work as written in most cases, but will need changes before the code can be recompiled.
Version History
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Revision 4, 2019-06-18 (Tobias Hector)
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Modified settings restrictions, see Version 4 API incompatibility
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Revision 3, 2018-09-11 (Alexander Galazin)
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Minor restructuring
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Revision 2, 2018-04-17 (Alexander Galazin)
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Added issues and resolutions
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Revision 1, 2018-04-11 (Alexander Galazin)
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Initial draft
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Document Notes
For more information, see the Vulkan Specification
This page is a generated document. Fixes and changes should be made to the generator scripts, not directly.