#include <instruction_selection.h>

Inheritance diagram for ArithCompareAdjustment:

Public Member Functions
	ArithCompareAdjustment (const PhvInfo &p)

Public Member Functions inherited from P4::PassManager
	PassManager (const PassManager &)=default

	PassManager (const std::initializer_list< VisitorRef > &init)

	PassManager (PassManager &&)=default

void	addDebugHook (DebugHook h, bool recursive=false)

void	addDebugHooks (std::vector< DebugHook > hooks, bool recursive=false)

void	addPasses (const std::initializer_list< VisitorRef > &init)

const IR::Node *	apply_visitor (const IR::Node , const char =0) override

bool	backtrack (trigger &trig) override

PassManager *	clone () const override

void	early_exit ()

void	listPasses (std::ostream &, cstring sep) const

bool	never_backtracks () override

void	removePasses (const std::vector< cstring > &exclude)

void	setStopOnError (bool stop)

Public Member Functions inherited from P4::Visitor
virtual bool	check_clone (const Visitor *a)

virtual bool	check_global (cstring)

virtual void	clear_globals ()

virtual ControlFlowVisitor *	controlFlowVisitor ()

virtual void	end_apply ()

virtual void	end_apply (const IR::Node *root)

virtual void	erase_global (cstring)

template<class T >
const T *	findContext () const

template<class T >
const T *	findContext (const Context *&c) const

template<class T >
const T *	findOrigCtxt () const

template<class T >
const T *	findOrigCtxt (const Context *&c) const

virtual Visitor &	flow_clone ()

virtual void	flow_merge (Visitor &)

virtual bool	flow_merge_closure (Visitor &)

virtual void	flow_merge_global_from (cstring)

virtual void	flow_merge_global_to (cstring)

const Context *	getChildContext () const

int	getChildrenVisited () const

const Context *	getContext () const

int	getContextDepth () const

const IR::Node *	getCurrentNode () const

template<class T >
const T *	getCurrentNode () const

const IR::Node *	getOriginal () const

template<class T >
const T *	getOriginal () const

template<class T >
const T *	getParent () const

virtual bool	has_flow_joins () const

profile_t	init_apply (const IR::Node root, const Context parent_context)

bool	isInContext (const IR::Node *n) const

virtual const char *	name () const

template<class T >
void	parallel_visit (const IR::Vector< T > &v, const char *name, int cidx)

template<class T >
void	parallel_visit (const IR::Vector< T > &v, const char *name=0)

template<class T >
void	parallel_visit (IR::Vector< T > &v, const char *name, int cidx)

template<class T >
void	parallel_visit (IR::Vector< T > &v, const char *name=0)

void	print_context () const

const Visitor &	setCalledBy (const Visitor *visitor)

void	setName (const char *name)

void	visit (const IR::Node &n, const char *name, int cidx)

void	visit (const IR::Node &n, const char *name=0)

void	visit (const IR::Node &n, const char name, int cidx)

void	visit (const IR::Node &n, const char name=0)

void	visit (const IR::Node const &n, const char name, int cidx)

void	visit (const IR::Node const &n, const char name=0)

void	visit (IR::Node &n, const char *name, int cidx)

void	visit (IR::Node &n, const char *name=0)

void	visit (IR::Node &, const char =0, int=0)

template<class T , typename = std::enable_if_t<Util::has_SourceInfo_v<T> && !std::is_pointer_v<T>>, class... Args>
void	warn (const int kind, const char *format, const T &node, Args &&...args)
	The const ref variant of the above.

template<class T , typename = std::enable_if_t<Util::has_SourceInfo_v<T>>, class... Args>
void	warn (const int kind, const char format, const T node, Args &&...args)

bool	warning_enabled (int warning_kind) const

Public Member Functions inherited from P4::Backtrack

Public Attributes
std::map< const PHV::Field *, int >	comp_adj_field_width_map

std::map< const IR::MAU::Action , std::set< const PHV::Field > >	comp_adj_fields_per_action_map

std::map< const cstring, int >	comp_adj_name_width_map

Public Attributes inherited from P4::Visitor
const Visitor *	called_by = nullptr

cstring	internalName

SplitFlowVisit_base *&	split_link

SplitFlowVisit_base *	split_link_mem = nullptr

Additional Inherited Members
Public Types inherited from P4::Visitor
typedef Visitor_Context	Context

Static Public Member Functions inherited from P4::Visitor
static cstring	demangle (const char *)

static bool	warning_enabled (const Visitor *visitor, int warning_kind)

Protected Member Functions inherited from P4::PassManager
profile_t	init_apply (const IR::Node *root) override

void	runDebugHooks (const char visitorName, const IR::Node node)

Protected Member Functions inherited from P4::Visitor
virtual void	init_join_flows (const IR::Node *)

virtual bool	join_flows (const IR::Node *)

virtual void	post_join_flows (const IR::Node , const IR::Node )

void	visit_children (const IR::Node *, std::function< void()> fn)

virtual void	visitAgain () const

virtual void	visitOnce () const

Protected Attributes inherited from P4::PassManager
safe_vector< DebugHook >	debugHooks

safe_vector< Visitor * >	passes

bool	running = false

unsigned	seqNo = 0

bool	stop_on_error = true

Protected Attributes inherited from P4::Visitor
bool	dontForwardChildrenBeforePreorder = false

bool	joinFlows = false

bool	visitDagOnce = true

Detailed Description

Applies two transformations to arithmetic compare operations:

Narrow write destinations are expanded to match the read field widths. Currently done by expanding the write field width. This should be changed in the future to add and write to padding.
A compare + set 0 that writes across all bits in a wide write target are merged into a single compare. (The compare must write to bit 0, and the set must write to bits width-1 .. 1 .)

These transformations are necessary because of the mismatch between P4 comparison operators and MAU arithmetic compare instructions. P4 comparison operators always produce a 1b boolean value. MAU compare instructions write to the entire PHV container: the LSB is set to the comparison result and all other bits are zeroed.

E.g.: header data_t { bit<8> f1; bit<8> f2; bit<8> f3; }

struct metadata { bool is_gt; };

action gt_action() { meta.is_gt = hdr.data.f1 > hdr.data.f2; hdr.data.f3 = (bit<8>)(bit<1>)(hdr.data.f1 > data.data.f2); }

This pass will:

Change the type of 'meta.is_gt' from bool to bit<8>. All references to 'meta.is_gt' other than the comparions would be replaced with 'meta.is_gt[0:0]'
The hdr.data.f3 action is translated to two IR::MAU:Instruction objects: set(ingress::hdr.data.f3[7:1], 0); gtu(ingress::hdr.data.f3[0:0], ingress::hdr.data.f1, ingress::hdr.data.f2); This is changed to: gtu(ingress::hdr.data.f3, ingress::hdr.data.f1, ingress::hdr.data.f2);

Details: This pass has two sub-passes: the first scans the design to find comparisons to transform, and the second applies the transforms.

Usage: This pass should be run after ElimAllButLastWrite. This ensures that only the last write to a location is used when verifying whether the comparison transforms can be safely applied.

Limitations:

Currently only works on metadata.

FIXME(glen): The first transformation currently expands the width of the write field to match the width of the read fields. This should be changed to add a pad field and then write to the pad + original field. Unfortunately the compiler doesn't currently support writing to more than one field with a single instruction.

MultiOperand seems an appropriate candidate to allow writes to multiple fields at the same time, but this require updates to the PHV allocation location logic and the dead code elimination logic.

Public Member Functions

Public Attributes

Additional Inherited Members

Detailed Description