Content related to stateful ALU. More...

Classes
class	BFN::RegisterReadWrite
	The pass replaces the Register.read/write() calls with register actions. More...

class	CreateSaluInstruction
	The pass creates SALU VLIW instructions. More...

Detailed Description

Content related to stateful ALU.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

SPDX-License-Identifier: Apache-2.0

A register is referred to as a stateful table.

Note that a stateful ALU (SALU) is referred to as meter ALU in micro-architecture specificaion (MAS) documents.

Represented by IR::MAU::StatefulAlu IR node.
Contains:
- Instruction memory:
  - Four rows, each one contains a SALU VLIW instruction represented by a register action in P4 code and IR::MAU::SaluAction IR node
    - The SALU VLIW instruction contains instructions for particular units (four sub-ALUs, two comparators, output sub-ALU) represented by primitives (IR::MAU::Primitive) both in backend and assembler.
- Register file:
  - Four rows, each one is 32b (Tofino) / 34b (Tofino 2) register represented by a register parameter in P4 code and IR::MAU::SaluRegfileRow IR node
  - Shared by "large" constants and register parameters
There are four SALUs in a MAU stage.

Front-end passes involved:

P4V1::StatefulAluConverter (fromv1.0 folder)
- Registered via singleton pattern
- Transforms the IR from P4-14 to P4-16
- E.g.
  blackbox stateful_alu reg_alu_4 {
  
  reg: reg_4;
  
  update_lo_1_value: register_lo + 1;
  
  }
  
  is transformed to
  RegisterAction<Picasso, bit<32>, bit<32>>(reg_4) Rembrandt = {
  
  void apply(inout Picasso Morrow, out bit<32> Elkton) {
  
  Morrow.lo = Morrow.lo + 1;
  
  }
  
  }

Mid-end passes involved:

P4::SynthesizeActions
- Moves the statements placed directly in an apply block of a control block to newly created @hidden actions (which are further placed into @hidden tables in the P4::MoveActionsToTables pass).
- BFN::ActionSynthesisPolicy checks whether successive statements in an apply block of a control block can be combined into a single new action. This is necessary for post-mid-end and back-end passes that process the actions independently of each other. The policy detects Register.write()-after-read(), which can be transformed into a single register action.
BFN::RegisterReadWrite (see the description of the sub-passes above)
1. BFN::RegisterReadWrite::MoveRegisterParameters
2. BFN::RegisterReadWrite::CollectRegisterReadsWrites
3. BFN::RegisterReadWrite::AnalyzeActionWithRegisterCalls
4. BFN::RegisterReadWrite::UpdateRegisterActionsAndExecuteCalls
5. BFN::RegisterReadWrite::CheckRegisterActions

Post-mid-end passes involved:

BFN::BridgedPacking and BFN::SubstitutePackedHeaders
- BFN::BackendConverter (converts mid-end IR into back-end IR)
  - BFN::ProcessBackendPipe
    - BFN::AttachTables (see the description of the sub-passes above)
      1. BFN::AttachTables::InitializeStatefulAlus
      2. BFN::AttachTables::InitializeRegisterParams
      3. BFN::AttachTables::InitializeStatefulInstructions
        
        CreateSaluInstruction
      4. BFN::AttachTables::DefineGlobalRefs

Class Documentation

◆ BFN::RegisterReadWrite

class BFN::RegisterReadWrite

The pass replaces the Register.read/write() calls with register actions.

The pass must be invoked prefereably towards the end of mid-end to account for any mid-end optimizations like constant folding, propogation, etc.

The subpass CheckRegisterActions checks the limit of number of RegisterActions attached to a single Register; not only of the RegisterActions introduced by the RegisterReadWrite pass.

Inheritance diagram for BFN::RegisterReadWrite:

[legend]

Public Member Functions
	RegisterReadWrite (P4::ReferenceMap refMap, P4::TypeMap typeMap, BFN::TypeChecking *typeChecking=nullptr)

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
Static Public Member Functions
static std::pair< const IR::MethodCallExpression , const IR::Expression >	extractRegisterReadWrite (const IR::Statement *reg_stmt)

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

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

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

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

cstring	internalName

SplitFlowVisit_base *&	split_link

SplitFlowVisit_base *	split_link_mem = nullptr

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

Member Function Documentation

◆ extractRegisterReadWrite()

std::pair< const IR::MethodCallExpression *, const IR::Expression * > BFN::RegisterReadWrite::extractRegisterReadWrite ( const IR::Statement * reg_stmt )

static

The method checks whether the form of the read/write register call is correct, i.e. has one of the forms described in the error message in this function.

Parameters

[in] reg_stmt The read/write register statement that is being checked

Returns

A pair of 1. the read/write method call expression contained in the reg_stmt, and

the left-hand side of the assignment statement of the register read method.

◆ CreateSaluInstruction

class CreateSaluInstruction

The pass creates SALU VLIW instructions.

The pass converts a RegisterAction into an MAU::SaluAction for an MAU::StatefulAlu, converting all of the properties and code into the corresponding instructions or whatever else is needed.

The pass is designed to be applied to a subtree of IR containing a single Declaration_Instance object of type RegisterAction, LearnAction, MinMaxAction or SelectorAction, and creates an SaluAction for it, adding it to the StatefulAlu passed to the pass constructor. We arrange for exactly one instance of this pass to be created for each SALU, and reuse it to create all the individual instructions in that SALU, so we can accumulate information about things that need to be shared between instructions here.

This is really a kind of "reconstruction transform" rather than an Inspector, but the normal Transform isn't right for it, as we want to rebuild some things with a very different object (turning Properties into Instructions) which won't work 'in place'. It also really wants to do pattern matching across expression trees, which our Visitor infrastructure does not support very well.

It can be thought of as a state machine + code accumulator that is run over the body of the register_action. The 'etype' state tracks what the currently visited expression is needed for (left or right side of an assignment, or condition in an 'if'). Operands of an instruction are accumulated, existence and uses of local variables are tracked, and instructions are generated and added to the body of the SaluAction that is being created. Along the way and at the end, various problems that exceeed the capabilities of the salu are diagnosed.

It also checks if an instruction about to be created can be merged with another existing instruction. The instructions must have the same opcode and operands, but their predicates can differ. The predicates are merged via | operation.

Inheritance diagram for CreateSaluInstruction:

[legend]

Public Member Functions
	CreateSaluInstruction (IR::MAU::StatefulAlu *salu)

Public Member Functions inherited from P4::Inspector
const IR::Node *	apply_visitor (const IR::Node , const char name=0) override

profile_t	init_apply (const IR::Node *root) override

virtual void	loop_revisit (const IR::Node *)

virtual void	postorder (const IR::Node *)

virtual bool	preorder (const IR::Node *)

virtual void	revisit (const IR::Node *)

void	revisit_visited ()

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

void	visitAgain () const override

void	visitOnce () const override

Public Member Functions inherited from P4::Visitor
virtual bool	check_global (cstring)

virtual void	clear_globals ()

virtual Visitor *	clone () const

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

Friends
std::ostream &	operator<< (std::ostream &out, CreateSaluInstruction::etype_t e)

std::ostream &	operator<< (std::ostream &out, CreateSaluInstruction::LocalVar::use_t u)

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)

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

cstring	internalName

SplitFlowVisit_base *&	split_link

SplitFlowVisit_base *	split_link_mem = nullptr

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)

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

bool	joinFlows = false

bool	visitDagOnce = true

Classes

Detailed Description

Class Documentation

◆ BFN::RegisterReadWrite

Public Member Functions

Static Public Member Functions

Additional Inherited Members

Member Function Documentation

◆ extractRegisterReadWrite()

◆ CreateSaluInstruction

Public Member Functions

Friends

Additional Inherited Members