llvm::pointer_union_detail Namespace Reference

Classes
class	PointerUnionMembers
	CRTP base that generates non-template constructors and assignment operators for each type in the union. More...
class	PointerUnionMembers< Derived, Idx >
class	PointerUnionMembers< Derived, Idx, Type, Types... >
struct	TagEntry
	Tag descriptor for one type in the union. More...

Functions
constexpr int	bitsRequired (unsigned NumValues)
	Determine the number of bits required to store values in [0, NumValues).
template<typename... Ts>
constexpr int	lowBitsAvailable ()
template<typename... PTs>
constexpr bool	useFixedWidthTags ()
	True if all types have enough low bits for a fixed-width tag.
template<typename... PTs>
constexpr bool	typesInNonDecreasingBitOrder ()
	True if types are in non-decreasing NumLowBitsAvailable order.
template<typename... PTs>
constexpr std::array< TagEntry, sizeof...(PTs)>	computeFixedTags ()
	Compute fixed-width tag table (all types have enough bits for the tag).
template<typename... PTs>
constexpr std::optional< std::array< TagEntry, sizeof...(PTs)> >	computeExtendedTags ()
	Compute variable-width tag table, or return std::nullopt if the types don't fit.

Function Documentation

bitsRequired()

int llvm::pointer_union_detail::bitsRequired ( unsigned NumValues )

constexpr

Determine the number of bits required to store values in [0, NumValues).

This is ceil(log2(NumValues)).

Definition at line 36 of file PointerUnion.h.

References llvm::bit_width_constexpr().

Referenced by computeFixedTags(), and useFixedWidthTags().

computeExtendedTags()

template<typename... PTs>

std::optional< std::array< TagEntry, sizeof...(PTs)> > llvm::pointer_union_detail::computeExtendedTags ( )

constexpr

Compute variable-width tag table, or return std::nullopt if the types don't fit.

Types must be in non-decreasing NumLowBitsAvailable order. Groups types by available bits into tiers; each non-final tier reserves its highest code as an escape prefix.

Example with 3 tiers (2-bit, 3-bit, 5-bit types): Tier 0 (2 bits): codes 0b00, 0b01, 0b10; escape = 0b11 Tier 1 (3 bits): codes 0b011, escape = 0b111 Tier 2 (5 bits): codes 0b00111, 0b01111, 0b10111, 0b11111

Definition at line 92 of file PointerUnion.h.

References I, and N.

computeFixedTags()

template<typename... PTs>

std::array< TagEntry, sizeof...(PTs)> llvm::pointer_union_detail::computeFixedTags ( )

constexpr

Compute fixed-width tag table (all types have enough bits for the tag).

For example, with 4 types and 3 available bits, the tag is 2 bits wide (values 0-3) and each entry has the same mask of 0x3.

Definition at line 70 of file PointerUnion.h.

References bitsRequired(), I, and N.

lowBitsAvailable()

template<typename... Ts>

int llvm::pointer_union_detail::lowBitsAvailable ( )

constexpr

Definition at line 40 of file PointerUnion.h.

Referenced by useFixedWidthTags().

typesInNonDecreasingBitOrder()

template<typename... PTs>

bool llvm::pointer_union_detail::typesInNonDecreasingBitOrder ( )

constexpr

True if types are in non-decreasing NumLowBitsAvailable order.

Definition at line 52 of file PointerUnion.h.

References I.

useFixedWidthTags()

template<typename... PTs>

bool llvm::pointer_union_detail::useFixedWidthTags ( )

constexpr

True if all types have enough low bits for a fixed-width tag.

Definition at line 46 of file PointerUnion.h.

References bitsRequired(), and lowBitsAvailable().

Referenced by llvm::PointerUnion< TrivialCallback *, NonTrivialCallbacks * >::PointerLikeTypeTraits.