Appendix A: Vulkan Environment for SPIRV
Shaders for Vulkan are defined by the Khronos SPIRV Specification as well as the Khronos SPIRV Extended Instructions for GLSL Specification. This appendix defines additional SPIRV requirements applying to Vulkan shaders.
Versions and Formats
A Vulkan 1.0 implementation must support the 1.0 version of SPIRV and the 1.0 version of the SPIRV Extended Instructions for GLSL.
A SPIRV module passed into vkCreateShaderModule is interpreted as a series of 32bit words in host endianness, with literal strings packed as described in section 2.2 of the SPIRV Specification. The first few words of the SPIRV module must be a magic number and a SPIRV version number, as described in section 2.3 of the SPIRV Specification.
Capabilities
The SPIRV capabilities listed below must be supported if the corresponding feature or extension is enabled, or if no features or extensions are listed for that capability. Extensions are only listed when there is not also a feature bit associated with that capability.
SPIRV OpCapability 
Vulkan feature or extension name 










































































































shaderDenormPreserveFloat16, shaderDenormPreserveFloat32, shaderDenormPreserveFloat64 

shaderDenormFlushToZeroFloat16, shaderDenormFlushToZeroFloat32, shaderDenormFlushToZeroFloat64 

shaderSignedZeroInfNanPreserveFloat16, shaderSignedZeroInfNanPreserveFloat32, shaderSignedZeroInfNanPreserveFloat64 

shaderRoundingModeRTEFloat16, shaderRoundingModeRTEFloat32, shaderRoundingModeRTEFloat64 

shaderRoundingModeRTZFloat16, shaderRoundingModeRTZFloat32, shaderRoundingModeRTZFloat64 
The application can pass a SPIRV module to vkCreateShaderModule that
uses the SPV_KHR_variable_pointers
SPIRV extension.
The application can pass a SPIRV module to vkCreateShaderModule that
uses the SPV_KHR_shader_draw_parameters
SPIRV extension.
The application can pass a SPIRV module to vkCreateShaderModule that
uses the SPV_KHR_8bit_storage
SPIRV extension.
The application can pass a SPIRV module to vkCreateShaderModule that
uses the
SPV_KHR_16bit_storage
SPIRV extension.
The application can pass a SPIRV module to vkCreateShaderModule that
uses the
SPV_KHR_float_controls
SPIRV extension.
The application can pass a SPIRV module to vkCreateShaderModule that
uses the
SPV_KHR_storage_buffer_storage_class
SPIRV extension.
The application can pass a SPIRV module to vkCreateShaderModule that
uses the SPV_KHR_vulkan_memory_model
SPIRV extension.
The application must not pass a SPIRV module containing any of the following to vkCreateShaderModule:

any OpCapability not listed above,

an unsupported capability, or

a capability which corresponds to a Vulkan feature or extension which has not been enabled.
Validation Rules within a Module
A SPIRV module passed to vkCreateShaderModule must conform to the following rules:

Every entry point must have no return value and accept no arguments.

Recursion: The static functioncall graph for an entry point must not contain cycles.

The Logical addressing model must be selected.

Scope for execution must be limited to:

Workgroup

Subgroup


Scope for memory must be limited to:

Device

If
vulkanMemoryModel
is enabled andvulkanMemoryModelDeviceScope
is not enabled, Device scope must not be used. 
If
vulkanMemoryModel
is not enabled, Device scope only extends to the queue family, not the whole device.


QueueFamilyKHR

If
vulkanMemoryModel
is not enabled, QueueFamilyKHR must not be used.


Workgroup

Invocation


Storage Class must be limited to:

UniformConstant

Input

Uniform

Output

Workgroup

Private

Function

PushConstant

Image

StorageBuffer


Memory semantics must obey the following rules:

Acquire must not be used with
OpAtomicStore
. 
Release must not be used with
OpAtomicLoad
. 
AcquireRelease must not be used with
OpAtomicStore
orOpAtomicLoad
. 
Sequentially consistent atomics and barriers are not supported and SequentiallyConsistent is treated as AcquireRelease. SequentiallyConsistent should not be used.

OpMemoryBarrier
must use one of Acquire, Release, AcquireRelease, or SequentiallyConsistent and must include at least one storage class. 
If the semantics for
OpControlBarrier
includes one of Acquire, Release, AcquireRelease, or SequentiallyConsistent, then it must include at least one storage class. 
SubgroupMemory, CrossWorkgroupMemory, and AtomicCounterMemory are ignored.


Any
OpVariable
with anInitializer
operand must have one of the following as its Storage Class operand:
Output

Private

Function


The
OriginLowerLeft
execution mode must not be used; fragment entry points must declareOriginUpperLeft
. 
The
PixelCenterInteger
execution mode must not be used. Pixels are always centered at halfinteger coordinates. 
Images and Samplers

OpTypeImage
must declare a scalar 32bit float or 32bit integer type for the “Sampled Type”. (RelaxedPrecision
can be applied to a sampling instruction and to the variable holding the result of a sampling instruction.) 
OpTypeImage
must have a “Sampled” operand of 1 (sampled image) or 2 (storage image). 
If shaderStorageImageReadWithoutFormat is not enabled and an
OpTypeImage
has “Image Format” operand ofUnknown
, any variables created with the given type must be decorated withNonReadable
. 
If shaderStorageImageWriteWithoutFormat is not enabled and an
OpTypeImage
has “Image Format” operand ofUnknown
, any variables created with the given type must be decorated withNonWritable
. 
OpImageQuerySizeLod
, andOpImageQueryLevels
must only consume an “Image” operand whose type has its “Sampled” operand set to 1. 
The (u,v) coordinates used for a
SubpassData
must be the <id> of a constant vector (0,0), or if a layer coordinate is used, must be a vector that was formed with constant 0 for the u and v components. 
The “Depth” operand of
OpTypeImage
is ignored. 
Objects of types
OpTypeImage
,OpTypeSampler
,OpTypeSampledImage
, and arrays of these types must not be stored to or modified.


Decorations

Any
BuiltIn
decoration not listed in BuiltIn Variables must not be used. 
Any
BuiltIn
decoration that corresponds only to Vulkan features or extensions that have not been enabled must not be used. 
The
GLSLShared
andGLSLPacked
decorations must not be used. 
The
Flat
,NoPerspective
,Sample
, andCentroid
decorations must not be used on variables with storage class other thanInput
or on variables used in the interface of nonfragment shader entry points. 
The
Patch
decoration must not be used on variables in the interface of a vertex, geometry, or fragment shader stage’s entry point. 
Only the roundtonearesteven and the roundtozero rounding modes can be used for the
FPRoundingMode
decoration. 
The
FPRoundingMode
decoration can only be used for the floatingpoint conversion instructions as described in theSPV_KHR_16bit_storage
SPIRV extension. 
DescriptorSet
andBinding
decorations must obey the constraints on storage class, type, and descriptor type described in DescriptorSet and Binding Assignment


OpTypeRuntimeArray
must only be used for:
the last member of an
OpTypeStruct
that is in theStorageBuffer
storage class decorated asBlock
, or that is in theUniform
storage class decorated asBufferBlock
.


Linkage: See Shader Interfaces for additional linking and validation rules.

Compute Shaders

For each compute shader entry point, either a
LocalSize
execution mode or an object decorated with theWorkgroupSize
decoration must be specified.


Atomic instructions must declare a scalar 32bit integer type, or a scalar 64bit integer type if the
Int64Atomics
capability is enabled, for the value pointed to by Pointer.
shaderBufferInt64Atomics must be enabled for 64bit integer atomic operations to be supported on a Pointer with a Storage Class of StorageBuffer or Uniform.

shaderSharedInt64Atomics must be enabled for 64bit integer atomic operations to be supported on a Pointer with a Storage Class of Workgroup.


The Pointer operand of all atomic instructions must have a Storage Class limited to:

Uniform

Workgroup

Image

StorageBuffer


If
separateDenormSettings
isVK_FALSE
, then the entry point must use the same denormals execution mode for both 16bit and 64bit floatingpoint types. 
If
separateRoundingModeSettings
isVK_FALSE
, then the entry point must use the same rounding execution mode for both 16bit and 64bit floatingpoint types. 
If
shaderSignedZeroInfNanPreserveFloat16
isVK_FALSE
, thenSignedZeroInfNanPreserve
for 16bit floatingpoint type must not be used. 
If
shaderSignedZeroInfNanPreserveFloat32
isVK_FALSE
, thenSignedZeroInfNanPreserve
for 32bit floatingpoint type must not be used. 
If
shaderSignedZeroInfNanPreserveFloat64
isVK_FALSE
, thenSignedZeroInfNanPreserve
for 64bit floatingpoint type must not be used. 
If
shaderDenormPreserveFloat16
isVK_FALSE
, thenDenormPreserve
for 16bit floatingpoint type must not be used. 
If
shaderDenormPreserveFloat32
isVK_FALSE
, thenDenormPreserve
for 32bit floatingpoint type must not be used. 
If
shaderDenormPreserveFloat64
isVK_FALSE
, thenDenormPreserve
for 64bit floatingpoint type must not be used. 
If
shaderDenormFlushToZeroFloat16
isVK_FALSE
, thenDenormFlushToZero
for 16bit floatingpoint type must not be used. 
If
shaderDenormFlushToZeroFloat32
isVK_FALSE
, thenDenormFlushToZero
for 32bit floatingpoint type must not be used. 
If
shaderDenormFlushToZeroFloat64
isVK_FALSE
, thenDenormFlushToZero
for 64bit floatingpoint type must not be used. 
If
shaderRoundingModeRTEFloat16
isVK_FALSE
, thenRoundingModeRTE
for 16bit floatingpoint type must not be used. 
If
shaderRoundingModeRTEFloat32
isVK_FALSE
, thenRoundingModeRTE
for 32bit floatingpoint type must not be used. 
If
shaderRoundingModeRTEFloat64
isVK_FALSE
, thenRoundingModeRTE
for 64bit floatingpoint type must not be used. 
If
shaderRoundingModeRTZFloat16
isVK_FALSE
, thenRoundingModeRTZ
for 16bit floatingpoint type must not be used. 
If
shaderRoundingModeRTZFloat32
isVK_FALSE
, thenRoundingModeRTZ
for 32bit floatingpoint type must not be used. 
If
shaderRoundingModeRTZFloat64
isVK_FALSE
, thenRoundingModeRTZ
for 64bit floatingpoint type must not be used. 
The
Base
operand ofOpPtrAccessChain
must point to one of the following storage classes:
Workgroup, if
VariablePointers
is enabled. 
StorageBuffer, if
VariablePointers
orVariablePointersStorageBuffer
is enabled. 
PhysicalStorageBufferEXT, if the
PhysicalStorageBuffer64EXT
addressing model is enabled.

Precision and Operation of SPIRV Instructions
The following rules apply to half, single, and doubleprecision floating point instructions:

Positive and negative infinities and positive and negative zeros are generated as dictated by IEEE 754, but subject to the precisions allowed in the following table.

Dividing a nonzero by a zero results in the appropriately signed IEEE 754 infinity.

Signaling NaNs are not required to be generated and exceptions are never raised. Signaling NaN may be converted to quiet NaNs values by any floating point instruction.

By default, the implementation may perform optimizations on half, single, or doubleprecision floatingpoint instructions respectively that ignore sign of a zero, or assume that arguments and results are not Nans or \(\pm\infty\), this doesn’t apply to
OpIsNan
andOpIsInf
, which must always correctly detect Nans and \(\pm\infty\). If the entry point is declared with theSignedZeroInfNanPreserve
execution mode, then sign of a zero, Nans, and \(\pm\infty\) must not be ignored.
The following core SPIRV instructions must respect the
SignedZeroInfNanPreserve
execution mode:OpPhi
,OpSelect
,OpReturnValue
,OpVectorExtractDynamic
,OpVectorInsertDynamic
,OpVectorShuffle
,OpCompositeConstruct
,OpCompositeExtract
,OpCompositeInsert
,OpCopyObject
,OpTranspose
,OpFConvert
,OpFNegate
,OpFAdd
,OpFSub
,OpFMul
,OpStore
. This execution mode must also be respected byOpLoad
except for loads from theInput
storage class in the fragment shader stage with the floatingpoint result type. Other SPIRV instruction may also respect theSignedZeroInfNanPreserve
execution mode.


Denormalized values are supported.

By default, any half, single, or doubleprecision denormalized value input into a shader or potentially generated by any instruction or any extended instructions for GLSL in a shader may be flushed to zero.

If the entry point is declared with the
DenormFlushToZero
execution mode then for the affected instuctions the denormalized result must be flushed to zero and the denormalized operands may be flushed to zero. Denormalized values obtained via unpacking an integer into a vector of values with smaller bit width and interpreting those values as floatingpoint numbers must be flushed to zero. 
The following core SPIRV instructions must respect the
DenormFlushToZero
execution mode:OpSpecConstantOp
(except when the opcode isOpQuantizeToF16
),OpFConvert
,OpFNegate
,OpFAdd
,OpFSub
,OpFMul
,OpFDiv
,OpFRem
,OpFMod
,OpVectorTimesScalar
,OpMatrixTimesScalar
,OpVectorTimesMatrix
,OpMatrixTimesVector
,OpMatrixTimesMatrix
,OpOuterProduct
,OpDot
; and the following extended instructions for GLSL:Round
,RoundEven
,Trunc
,FAbs
,Floor
,Ceil
,Fract
,Radians
,Degrees
,Sin
,Cos
,Tan
,Asin
,Acos
,Atan
,Sinh
,Cosh
,Tanh
,Asinh
,Acosh
,Atanh
,Atan2
,Pow
,Exp
,Log
,Exp2
,Log2
,Sqrt
,InverseSqrt
,Determinant
,MatrixInverse
,Modf
,ModfStruct
,FMin
,FMax
,FClamp
,FMix
,Step
,SmoothStep
,Fma
,UnpackHalf2x16
,UnpackDouble2x32
,Length
,Distance
,Cross
,Normalize
,FaceForward
,Reflect
,Refract
,NMin
,NMax
,NClamp
. Other SPIRV instruction may also respect theDenormFlushToZero
execution mode. 
The following core SPIRV instructions must respect the
DenormPreserve
execution mode:OpPhi
,OpSelect
,OpReturnValue
,OpVectorExtractDynamic
,OpVectorInsertDynamic
,OpVectorShuffle
,OpCompositeConstruct
,OpCompositeExtract
,OpCompositeInsert
,OpCopyObject
,OpTranspose
,OpStore
,OpSpecConstantOp
,OpFConvert
,OpFNegate
,OpFAdd
,OpFSub
,OpFMul
,OpVectorTimesScalar
,OpMatrixTimesScalar
,OpVectorTimesMatrix
,OpMatrixTimesVector
,OpMatrixTimesMatrix
,OpOuterProduct
,OpDot
,OpFOrdEqual
,OpFUnordEqual
,OpFOrdNotEqual
,OpFUnordNotEqual
,OpFOrdLessThan
,OpFUnordLessThan
,OpFOrdGreaterThan
,OpFUnordGreaterThan
,OpFOrdLessThanEqual
,OpFUnordLessThanEqual
,OpFOrdGreaterThanEqual
,OpFUnordGreaterThanEqual
; and the following extended instructions for GLSL:FAbs
,FSign
,Radians
,Degrees
,FMin
,FMax
,FClamp
,FMix
,Fma
,PackHalf2x16
,PackDouble2x32
,UnpackHalf2x16
,UnpackDouble2x32
,NMin
,NMax
,NClamp
. This execution mode must also be respected byOpLoad
except for loads from theInput
storage class in the fragment shader stage with the floatingpoint result type. Other SPIRV instruction may also respect theDenormPreserve
execution mode.

The precision of doubleprecision instructions is at least that of single precision.
The precision of operations is defined either in terms of rounding, as an error bound in ULP, or as inherited from a formula as follows.
Operations described as “correctly rounded” will return the infinitely
precise result, x, rounded so as to be representable in
floatingpoint.
The rounding mode is not specified, unless the entry point is declared with
the RoundingModeRTE
or the RoundingModeRTZ
execution mode.
These execution modes affect only correctly rounded SPIRV instructions.
These execution modes do not affect OpQuantizeToF16
.
If the rounding mode is not specified then this rounding is implementation
specific, subject to the following rules.
If x is exactly representable then x will be returned.
Otherwise, either the floatingpoint value closest to and no less than
x or the value closest to and no greater than x will be
returned.
Where an error bound of n ULP (units in the last place) is given, for an operation with infinitely precise result x the value returned must be in the range [x  n * ulp(x), x + n * ulp(x)]. The function ulp(x) is defined as follows:

If there exist nonequal floatingpoint numbers a and b such that a ≤ x ≤ b then ulp(x) is the minimum possible distance between such numbers, \(ulp(x) = \mathrm{min}_{a,b}  b  a \). If such numbers do not exist then ulp(x) is defined to be the difference between the two finite floatingpoint numbers nearest to x.
Where the range of allowed return values includes any value of magnitude larger than that of the largest representable finite floatingpoint number, operations may, additionally, return either an infinity of the appropriate sign or the finite number with the largest magnitude of the appropriate sign. If the infinitely precise result of the operation is not mathematically defined then the value returned is undefined.
Where an operation’s precision is described as being inherited from a
formula, the result returned must be at least as accurate as the result of
computing an approximation to x using a formula equivalent to the
given formula applied to the supplied inputs.
Specifically, the formula given may be transformed using the mathematical
associativity, commutativity and distributivity of the operators involved to
yield an equivalent formula.
The SPIRV precision rules, when applied to each such formula and the given
input values, define a range of permitted values.
If NaN is one of the permitted values then the operation may return
any result, otherwise let the largest permitted value in any of the ranges
be F_{max} and the smallest be F_{min}.
The operation must return a value in the range [x  E, x + E] where
\(E = \mathrm{max} \left(  x  F_{\mathrm{min}} ,  x 
F_{\mathrm{max}}  \right) \).
If the entry point is declared with the DenormFlushToZero
execution
mode, then any intermediate denormal value(s) while evaluating the formula
may be flushed to zero.
Denormal final results must be flushed to zero.
If the entry point is declared with the DenormPreserve
execution mode,
then denormals must be preserved throughout the formula.
For half (16 bit) and single (32 bit) precision instructions, precisions are required to be at least as follows:
Instruction  Single precision, unless decorated with RelaxedPrecision  Half precision 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Inherited from \(\sum_{i = 0}^{n  1} x_{i} \times y_{i}\). 


Correct result. 


Correct result. 


Correct result. 


Correct result. 


Correct result. 


2.5 ULP for y in the range [2^{126}, 2^{126}]. 
2.5 ULP for y in the range [2^{14}, 2^{14}]. 

Inherited from x  y × trunc(x/y), for y in the range [2^{126}, 2^{126}]. 
Inherited from x  y × trunc(x/y), for y in the range [2^{14}, 2^{14}]. 

Inherited from x  y × floor(x/y), for y in the range [2^{126}, 2^{126}]. 
Inherited from x  y × floor(x/y), for y in the range [2^{14}, 2^{14}]. 
conversions between types 
Correctly rounded. 
Note
The 
Instruction  Single precision, unless decorated with RelaxedPrecision  Half precision 


Inherited from 


3 + 2 × x ULP. 
1 + 2 × x ULP. 

3 ULP outside the range [0.5, 2.0]. Absolute error < 2^{21} inside the range [0.5, 2.0]. 
3 ULP outside the range [0.5, 2.0]. Absolute error < 2^{7} inside the range [0.5, 2.0]. 

Inherited from 


Inherited from 1.0 / 


2 ULP. 


Inherited from \(\frac{x \times \pi}{180}\). 


Inherited from \(\frac{x \times 180}{\pi}\). 


Absolute error \(\leq 2^{11}\) inside the range \([\pi, \pi]\). 
Absolute error \(\leq 2^{7}\) inside the range \([\pi, \pi]\). 

Absolute error \(\leq 2^{11}\) inside the range \([\pi, \pi]\). 
Absolute error \(\leq 2^{7}\) inside the range \([\pi, \pi]\). 

Inherited from \(\frac{sin()}{cos()}\). 


Inherited from \(atan2(x, sqrt(1.0  x^2))\). 


Inherited from \(atan2(sqrt(1.0  x^2), x)\). 


4096 ULP 
5 ULP. 

Inherited from \((exp(x)  exp(x)) \times 0.5\). 


Inherited from \((exp(x) + exp(x)) \times 0.5\). 


Inherited from \(\frac{sinh()}{cosh()}\). 


Inherited from \(log(x + sqrt(x^2 + 1.0))\). 


Inherited from \(log(x + sqrt(x^2  1.0))\). 


Inherited from \(log(\frac{1.0 + x}{1.0  x}) \times 0.5\). 


Correctly rounded. 


Correctly rounded. 


Inherited from \(sqrt(dot(x, x))\). 


Inherited from \(length(x  y)\). 


Inherited from 


Inherited from \(\frac{x}{length(x)}\). 


Correctly rounded. 


Inherited from x  2.0 × 


Inherited from eta × I  (eta × 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 


Inherited from x × (1.0  a) + y × a. 


Correctly rounded. 


Inherited from t × t × (3.0  2.0 × t), where \(t = clamp(\frac{x  edge0}{edge1  edge0}, 0.0, 1.0)\). 


Correctly rounded. 


Correctly rounded. 


Correctly rounded. 
GLSL.std.450 extended instructions specifically defined in terms of the above instructions inherit the above errors. GLSL.std.450 extended instructions not listed above and not defined in terms of the above have undefined precision. These include, for example, the trigonometric functions and determinant.
For the OpSRem
and OpSMod
instructions, if either operand is
negative the result is undefined.
Note
While the 
Compatibility Between SPIRV Image Formats And Vulkan Formats
Images which are read from or written to by shaders must have SPIRV image formats compatible with the Vulkan image formats backing the image under the circumstances described for texture image validation. The compatibile formats are:
SPIRV Image Format  Compatible Vulkan Format 














































































