imm_atomic_cmp_exch (sm5 - asm)

Immediate compare and exchange to memory.

imm_atomic_cmp_exch dst0[.single_component_mask], dst1, dstAddress[.swizzle], src0[.select_component], src1[.select_component]

Item	Description
dst0	[out] Contains dst1 before the write.
dst1	[in] An unordered access view (UAV) (u#). In the compute shader this can also be thread group shared memory (g#).
dstAddress	[in] The destination memory.
src0	[in] The value to compare to dst1.
src1	[in] The value written to the destination memory if the compared values are identical.

This instruction performs a single component 32-bit value compare of operand src0 with dst1 at 32-bit per component address dstAddress.

If dst1 is a u#, it may have been declared as raw, typed or structured. If typed, it must be declared as UINT/SINT with the bound resource format being R32_UINT/_SINT.

If dst1 is g#, it must be declared as raw or structured.

If the compared values are identical, the single-component 32-bit value in src1 is written to the destination memory. Otherwise, the destination memory is not changed.

The original 32-bit value in the destination memory is always written to dst0.

The entire operation is performed atomically.

If the shader invocation is inactive, for example if the pixel has been discarded earlier in its execution, or a pixel/sample invocation only exists to serve as a helper to a real pixel/sample for derivatives, this instruction does not alter the dst1 memory at all, and the returned value is undefined.

Out of bounds addressing on u# causes nothing to be written to memory, except if the u# is structured, and byte offset into the struct (second component of the address) is causing the out of bounds access, then the entire contents of the UAV become undefined.

Out of bounds addressing on u# or g# causes an undefined result to be returned to the shader in dst0.

This instruction applies to the following shader stages:

Vertex	Hull	Domain	Geometry	Pixel	Compute
				X	X

Because UAVs are available at all shader stages for Direct3D 11.1, this instruction applies to all shader stages for the Direct3D 11.1 runtime, which is available starting with Windows 8.

Vertex	Hull	Domain	Geometry	Pixel	Compute
X	X	X	X	X	X

Minimum Shader Model

This instruction is supported in the following shader models:

Shader Model	Supported
Shader Model 5	yes
Shader Model 4.1	no
Shader Model 4	no
Shader Model 3 (DirectX HLSL)	no
Shader Model 2 (DirectX HLSL)	no
Shader Model 1 (DirectX HLSL)	no

Related topics

Shader Model 5 Assembly (DirectX HLSL)