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P4C
The P4 Compiler
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P4C
The P4 Compiler
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#include <action_format.h>
Public Member Functions | |
| virtual bool | can_merge (const Parameter *param) const |
| bool | can_overlap_ranges (le_bitrange my_range, le_bitrange ad_range, le_bitrange &overlap, le_bitrange *my_overlap, le_bitrange *ad_overlap) const |
| cstring | cond_name () const |
| virtual void | dbprint (std::ostream &out) const =0 |
| bool | equiv_cond (const Parameter *p) const |
| virtual bool | equiv_value (const Parameter *, bool check_cond=true) const =0 |
| virtual bool | from_p4_program () const =0 |
| virtual const Parameter * | get_extended_param (uint32_t extension, const Parameter *) const =0 |
| template<typename T > | |
| bool | is () const |
| bool | is_cond_type (ModConditionally_t type) const |
| virtual bool | is_next_bit_of_param (const Parameter *, bool same_alias) const =0 |
| virtual bool | is_subset_of (const Parameter *param) const |
| virtual const Parameter * | merge (const Parameter *param) const |
| virtual cstring | name () const =0 |
| virtual bool | only_one_overlap_solution () const =0 |
| virtual const Parameter * | overlap (const Parameter *ad, bool guaranteed_one_overlap, le_bitrange *my_overlap, le_bitrange *ad_overlap) const =0 |
| void | set_cond (const Parameter *p) |
| void | set_cond (ModConditionally_t ct, cstring n) |
| virtual int | size () const =0 |
| virtual const Parameter * | split (int lo, int hi) const =0 |
| template<typename T > | |
| const T * | to () const |
 Public Member Functions inherited from P4::IHasDbPrint | |
| void | print () const |
Protected Attributes | |
| cstring | _cond_name |
| ModConditionally_t | _cond_type = NONE |
The purpose of this class is the base abstract class for any parameter that can appear as any section of bits on the action data bus. This by itself does not coordinate to any particular location in the bus or relationship to PHV, but is just information that can be classified as ActionData
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pure virtual |
Implements P4::IHasDbPrint.
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pure virtual |
Implemented in ActionData::Constant.
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pure virtual |
Implemented in ActionData::Constant.
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pure virtual |
Implemented in ActionData::Argument, ActionData::Constant, ActionData::Hash, ActionData::MeterALU, and ActionData::RandomNumber.
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protected |
A modify_field_conditionally in p4-14, which is converted to a ternary operation in p4-16 is done in the following manner. The instruction is converted to a bitmasked-set, with the even action data bus location being the parameter, and the odd action data bus location being the conditional mask.
bitmasked-set, described in uArch 15.1.3.8 Bit maskable set can be thought of as the following: dest = (src1 & mask) | (src2 & ~mask)
where the mask is directly stored on the RAM line, and is used on the action data bus.
The mask is stored at the odd word, so in the case of a conditional set, the driver can update the mask as it would any other parameter. However, at the even word, it is not just src1 stored, but src1 & mask. The mask stored at the second word is used as the background. Thus, if the condition is true, src1 will equal the parameter, but if the condition is false, src1 will be 0.
This leads to the following issue. Say you had a P4 action:
action a1(bit<8> p1, bool cond) { hdr.f1 = p1; hdr.f2 = cond ? p1 : hdr.f2; }
While previously, the data space for parameter p1 could have been shared, because of the condition, these have to be completely separate spaces on the RAM line, as the p1 in the second instruction could sometimes be zero. The rule is the following:
Data is only equivalent when both the original parameter and the condition that is controlling that parameter are equivalent.
1.12.0