P4C
The P4 Compiler
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AdjustShiftInstructions Class Reference

#include <instruction_adjustment.h>

Inheritance diagram for AdjustShiftInstructions:
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Public Member Functions

 AdjustShiftInstructions (const PhvInfo &p)
 
- Public Member Functions inherited from P4::Transform
const IR::Nodeapply_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 const IR::Nodepostorder (IR::Node *n)
 
virtual const IR::Nodepreorder (IR::Node *n)
 
void prune ()
 
virtual void revisit (const IR::Node *, const IR::Node *)
 
void revisit_visited ()
 
bool visit_in_progress (const IR::Node *) 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 Visitorclone () const
 
virtual ControlFlowVisitorcontrolFlowVisitor ()
 
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 Visitorflow_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 ContextgetChildContext () const
 
int getChildrenVisited () const
 
const ContextgetContext () const
 
int getContextDepth () const
 
const IR::NodegetCurrentNode () const
 
template<class T >
const T * getCurrentNode () const
 
const IR::NodegetOriginal () 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 VisitorsetCalledBy (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
 

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 Visitorcalled_by = nullptr
 
cstring internalName
 
SplitFlowVisit_base *& split_link
 
SplitFlowVisit_basesplit_link_mem = nullptr
 
- Protected Member Functions inherited from P4::Transform
const IR::Nodetransform_child (const IR::Node *child)
 
- 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::Transform
bool forceClone = false
 
- Protected Attributes inherited from P4::Visitor
bool dontForwardChildrenBeforePreorder = false
 
bool joinFlows = false
 
bool visitDagOnce = true
 

Detailed Description

The purpose of this pass is to adjust shift instruction that only write to a single slice but sourced from multiple containers. This is only seen with signed shifted right operation currently since all of the unsigned shift operation are either sliced or splitted. This pass have to adjust the operation, shift value and slice boundary to match the expected result. For example these P4_14 lines: header_type my_header_t { fields { a: 32; } } header my_header_t my_header; header_type my_md_t { fields { a: 32 (signed); } } ... modify_field_with_shift(my_header.a, my_md.a, 9, 0xff);

Will be translated by the compiler to this operation: instruction:shrs(ingress::my_header.a[7:0], ingress::my_md.a[7:0], 9);

As we can see, this operation does not make any sense but the compiler does not decode the shift value to adjust the slice so the source and destination slice will always be at the same position regardless of the shift value. This pass will translate such instructions using shrs, set or funnel-shift depending on the situation. The example above will get translated to: instruction:funnel-shift(ingress::my_header.a[7:0], ingress::my_md.a[23:16], ingress::my_md.a[15:8], 1)