Implement the `WaveActiveSum` HLSL Function

[llvm-beanz]

• Implement WaveActiveSum clang builtin,
• Link WaveActiveSum clang builtin with hlsl_intrinsics.h
• Add sema checks for WaveActiveSum to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for WaveActiveSum to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/WaveActiveSum.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/WaveActiveSum-errors.hlsl
• Create the int_dx_WaveActiveSum intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_WaveActiveSum to 119 in DXIL.td
• Create the WaveActiveSum.ll and WaveActiveSum_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_WaveActiveSum intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the WaveActiveSum lowering and map it to int_spv_WaveActiveSum in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/WaveActiveSum.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
119	WaveActiveOp	6.0	('library', 'compute', 'amplification', 'mesh', 'pixel', 'vertex', 'hull', 'domain', 'geometry', 'raygeneration', 'intersection', 'anyhit', 'closesthit', 'miss', 'callable', 'node')

SPIR-V

OpGroupNonUniformFAdd:

Description:

A floating point add group operation of all Value
operands contributed by active invocations in the
group.

Result Type must be a scalar or vector of floating-point
type.

Execution is a Scope that identifies the group of
invocations affected by this command. It must be Subgroup.

The identity I for Operation is 0. If Operation is
ClusteredReduce, ClusterSize must be present.

The type of Value must be the same as Result Type. The method used
to perform the group operation on the contributed Value(s) from active
invocations is implementation defined.

ClusterSize is the size of cluster to use. ClusterSize must be a
scalar of integer type, whose Signedness operand is 0.
ClusterSize must come from a constant
instruction. Behavior is undefined unless
ClusterSize is at least 1 and a power of 2. If ClusterSize is
greater than the size of the group, executing this instruction
results in undefined behavior.

Capability:
GroupNonUniformArithmetic, GroupNonUniformClustered,
GroupNonUniformPartitionedNV

Missing before version 1.3.

Word Count	Opcode	Results	Operands
6 + variable	350	<id> Result Type	Result <id>	Scope <id> Execution	Group Operation Operation	<id> Value	Optional <id> ClusterSize

Test Case(s)

Example 1

//dxc WaveActiveSum_test.hlsl -T lib_6_8 -E fn -enable-16bit-types -spirv -fspv-target-env=universal1.5 -fcgl -O0

export float4 fn(float4 p1) {
    return WaveActiveSum(p1);
}

Example 2

//dxc WaveActiveSum_1_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export uint4 fn(uint4 p1) {
    return WaveActiveSum(p1);
}

Example 3

//dxc WaveActiveSum_2_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export int4 fn(int4 p1) {
    return WaveActiveSum(p1);
}

HLSL:

Sums up the value of the expression across all active lanes in the current wave and replicates it to all lanes in the current wave.

Syntax

<type> WaveActiveSum(
   <type> expr
);

Parameters

expr

The expression to evaluate.

Return value

The sum value.

Remarks

The order of operations is undefined.

This function is supported from shader model 6.0 in all shader stages.

 

Examples

float3 total = WaveActiveSum( position ); // sum positions in wave
float3 center = total/count;           // compute average of these positions

See also

Overview of Shader Model 6

Shader Model 6

[damyanp]

Marking re-estimate this. Since this was originally refined, we have a different approach to implementing intrinsics and the way we've been estimating intrinsics has changed quite a bit.