Implement the `pack_u8` HLSL Function

[farzonl]

• Implement pack_u8 clang builtin,
• Link pack_u8 clang builtin with hlsl_intrinsics.h
• Add sema checks for pack_u8 to CheckHLSLBuiltinFunctionCall in SemaChecking.cpp
• Add codegen for pack_u8 to EmitHLSLBuiltinExpr in CGBuiltin.cpp
• Add codegen tests to clang/test/CodeGenHLSL/builtins/pack_u8.hlsl
• Add sema tests to clang/test/SemaHLSL/BuiltIns/pack_u8-errors.hlsl
• Create the int_dx_pack_u8 intrinsic in IntrinsicsDirectX.td
• Create the DXILOpMapping of int_dx_pack_u8 to 220 in DXIL.td
• Create the pack_u8.ll and pack_u8_errors.ll tests in llvm/test/CodeGen/DirectX/
• Create the int_spv_pack_u8 intrinsic in IntrinsicsSPIRV.td
• In SPIRVInstructionSelector.cpp create the pack_u8 lowering and map it to int_spv_pack_u8 in SPIRVInstructionSelector::selectIntrinsic.
• Create SPIR-V backend test case in llvm/test/CodeGen/SPIRV/hlsl-intrinsics/pack_u8.ll

DirectX

DXIL Opcode	DXIL OpName	Shader Model	Shader Stages
220	Pack4x8	6.6	()

SPIR-V

OpBitcast:

Description:

Bit pattern-preserving type conversion.

Result Type must be an OpTypePointer, or a
scalar or vector of numerical-type.

Operand must have a type of OpTypePointer, or a
scalar or vector of numerical-type. It must be a
different type than Result Type.

Before version 1.5: If either Result Type or Operand is a
pointer, the other must be a pointer or an integer scalar.
Starting with version 1.5: If either Result Type or Operand is a
pointer, the other must be a pointer, an integer scalar, or an integer
vector.

If both Result Type and the type of Operand are pointers, they both
must point into same storage class.

Behavior is undefined if the storage class of Result
Type does not match the one used by the operation that produced the
value of Operand.

If Result Type has the same number of components as Operand, they
must also have the same component width, and results are computed per
component.

If Result Type has a different number of components than Operand,
the total number of bits in Result Type must equal the total number of
bits in Operand. Let L be the type, either Result Type or
Operand’s type, that has the larger number of components. Let S be
the other type, with the smaller number of components. The number of
components in L must be an integer multiple of the number of
components in S. The first component (that is, the only or
lowest-numbered component) of S maps to the first components of L,
and so on, up to the last component of S mapping to the last
components of L. Within this mapping, any single component of S
(mapping to multiple components of L) maps its lower-ordered bits to
the lower-numbered components of L.

Word Count	Opcode	Results	Operands
4	124	<id> Result Type	Result <id>	<id> Operand

Test Case(s)

Example 1

//dxc pack_u8_test.hlsl -T lib_6_8 -enable-16bit-types -O0

export uint8_t4_packed fn(int4 p1) {
    return pack_u8(p1);
}

HLSL:

Syntax

p32u8 pack_u8(any_int16or32<4> v);

Type Description

Name	Template Type	Component Type	Size
ret	scalar	uint8_t4_packed	1
v	vector	int, int16_t, uint, or uint16_t	4

Minimum Shader Model

This function is supported in the following shader models.

Shader Model	Supported
Shader Model 6.6 and higher shader models	yes

Shader Stages

See also

• Intrinsic Functions (DirectX HLSL)
• See Pack Intrinsics