p4lang · fruffy · Apr 12, 2025 · May 20, 2025 · May 20, 2025 · Jun 18, 2025
diff --git a/.bazelrc b/.bazelrc
@@ -3,9 +3,9 @@ common --enable_workspace
 # Enable once #5066 is resolved.
 common --noenable_bzlmod
 
-# Use C++17.
-build --cxxopt=-std=c++17
-build --host_cxxopt=-std=c++17
+# Use C++20.
+build --cxxopt=-std=c++20
+build --host_cxxopt=-std=c++20
 
 # Force the use of Clang for all builds.
 build --action_env=CC=clang

diff --git a/.clang-format b/.clang-format
@@ -11,7 +11,7 @@ IncludeBlocks: Regroup
 # Force pointers to the type for C++.
 DerivePointerAlignment: false
 PointerAlignment: Right
-Standard: c++17
+Standard: c++20
 IncludeCategories:
   # Matches common headers first and sorts them before project includes
   - Regex: '^<.+/.*\.h>'

diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -24,8 +24,8 @@ endif()
 
 project (P4C)
 
-# set (CMAKE_CXX_EXTENSIONS OFF) # prefer using -std=c++17 rather than -std=gnu++17
-set (CMAKE_CXX_STANDARD 17)
+# set (CMAKE_CXX_EXTENSIONS OFF) # prefer using -std=c++20 rather than -std=gnu++20
+set (CMAKE_CXX_STANDARD 20)
 set (CMAKE_CXX_STANDARD_REQUIRED ON)
 
 set (CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake)

diff --git a/backends/tofino/bf-asm/asm-types.h b/backends/tofino/bf-asm/asm-types.h
@@ -183,11 +183,6 @@ inline bool operator==(int a, const struct value_t &b) { return b.type == tINT &
 
 inline const char *value_desc(const value_t &v) { return value_desc(&v); }
 
-template <class A, class B>
-inline bool operator!=(A a, B b) {
-    return !(a == b);
-}
-
 inline value_t &VECTOR(value_t)::operator[](int i) const {
     assert(i >= 0 && i < size);
     return data[i];
@@ -410,7 +405,7 @@ class MapIterChecked {
         iter(MapIterChecked *s, pair_t *p_) : self(s), p(p_) { check(); }
         pair_t &operator*() const { return *p; }
         pair_t *operator->() const { return p; }
-        bool operator==(iter &a) const { return p == a.p; }
+        bool operator==(const iter &a) const { return p == a.p; }
         iter &operator++() {
             p++;
             check();

diff --git a/backends/tofino/bf-asm/atcam_match.cpp b/backends/tofino/bf-asm/atcam_match.cpp
@@ -365,7 +365,8 @@ void AlgTcamMatchTable::write_regs_vt(REGS &regs) {
     }
 }
 
-std::unique_ptr<json::vector> AlgTcamMatchTable::gen_memory_resource_allocation_tbl_cfg() const {
+std::unique_ptr<json::vector> AlgTcamMatchTable::gen_memory_resource_allocation_tbl_cfg_no_input()
+    const {
     if (col_priority_way.size() == 0)
         error(lineno, "No column priority determined for table %s", name());
     unsigned fmt_width = format ? (format->size + 127) / 128 : 0;
@@ -427,7 +428,7 @@ void AlgTcamMatchTable::gen_unit_cfg(json::vector &units, int size) const {
     // Assuming atcam next hit table cannot be multiple tables
     stage_tbl["default_next_table"] =
         !hit_next.empty() ? hit_next[0].next_table_id() : Target::END_OF_PIPE();
-    stage_tbl["memory_resource_allocation"] = gen_memory_resource_allocation_tbl_cfg();
+    stage_tbl["memory_resource_allocation"] = gen_memory_resource_allocation_tbl_cfg_no_input();
     // Hash functions not necessary currently for ATCAM matches, as the result comes from
     // the partition_field_name
     stage_tbl["hash_functions"] = json::vector();

diff --git a/backends/tofino/bf-asm/deparser.cpp b/backends/tofino/bf-asm/deparser.cpp
@@ -30,9 +30,6 @@
 unsigned Deparser::unique_field_list_handle;
 Deparser Deparser::singleton_object;
 
-Deparser::Deparser() : Section("deparser") {}
-Deparser::~Deparser() {}
-
 struct Deparser::FDEntry {
     struct Base {
         virtual ~Base() {}
@@ -202,6 +199,9 @@ struct Deparser::FDEntry {
     void check(bitvec &phv_use) { what->check(phv_use); }
 };
 
+Deparser::Deparser() : Section("deparser") {}
+Deparser::~Deparser() = default;
+
 struct Deparser::Intrinsic::Type {
     target_t target;
     gress_t gress;

diff --git a/backends/tofino/bf-asm/exact_match.cpp b/backends/tofino/bf-asm/exact_match.cpp
@@ -471,7 +471,8 @@ void ExactMatchTable::gen_tbl_cfg(json::vector &out) const {
             unsigned ram_depth = way.rams.at(0).isLamb() ? LAMB_DEPTH : SRAM_DEPTH;
             way_tbl["size"] = way.rams.size() / fmt_width * format->groups() * ram_depth;
             add_pack_format(way_tbl, format.get(), false);
-            way_tbl["memory_resource_allocation"] = gen_memory_resource_allocation_tbl_cfg(way);
+            way_tbl["memory_resource_allocation"] =
+                gen_memory_resource_allocation_tbl_cfg_with_way(way);
             way_stage_tables.push_back(std::move(way_tbl));
         }
     }

diff --git a/backends/tofino/bf-asm/gtest/gtestasm.cpp b/backends/tofino/bf-asm/gtest/gtestasm.cpp
@@ -59,7 +59,7 @@ class GTestOptions : public Util::Options {
             },
             "[Compiler debugging] Adjust logging level per file (see below)");
     }
-    std::vector<const char *> *process(int argc, char *const argv[]) {
+    std::vector<const char *> *process(int argc, char *const argv[]) override {
         auto remainingOptions = Util::Options::process(argc, argv);
         return remainingOptions;
     }

diff --git a/backends/tofino/bf-asm/input_xbar.h b/backends/tofino/bf-asm/input_xbar.h
@@ -280,7 +280,7 @@ class InputXbar {
             : outer(o), outer_end(oend), inner_valid(false) {
             mk_inner_valid();
         }
-        bool operator==(const all_iter &a) {
+        bool operator==(const all_iter &a) const {
             if (outer != a.outer) return false;
             if (inner_valid != a.inner_valid) return false;
             return inner_valid ? inner == a.inner : true;

diff --git a/backends/tofino/bf-asm/json.h b/backends/tofino/bf-asm/json.h
@@ -296,7 +296,7 @@ class vector : public obj, public vector_base {
     }
 };
 
-typedef ordered_map<obj *, std::unique_ptr<obj>, obj::ptrless> map_base;
+using map_base = ordered_map<obj *, std::unique_ptr<obj>, obj::ptrless>;
 class map : public obj, public map_base {
  public:
     map() {}

diff --git a/backends/tofino/bf-asm/misc.h b/backends/tofino/bf-asm/misc.h
@@ -18,16 +18,12 @@
 #ifndef BACKENDS_TOFINO_BF_ASM_MISC_H_
 #define BACKENDS_TOFINO_BF_ASM_MISC_H_
 
-#include <iomanip>
-#include <limits>
 #include <memory>
 #include <sstream>
 #include <string>
 #include <type_traits>
 #include <vector>
 
-#include <boost/numeric/conversion/converter.hpp>
-
 #include "asm-types.h"
 #include "backends/tofino/bf-asm/json.h"
 
@@ -152,8 +148,8 @@ bool check_range_strict(value_t value, IntType lo, IntType hi) {
 
     /* -- Handle different ranges (signed, unsigned, different size) of the value_t::i
      *    and IntType. */
-    typedef boost::numeric::converter<IntType, decltype(value_t::i)> Converter;
-    if (Converter::out_of_range(value.i)) {
+
+    if (!std::in_range<IntType>(value.i)) {
         format_error_message(value, lo, hi);
         return false;
     }

diff --git a/backends/tofino/bf-asm/proxy_hash.cpp b/backends/tofino/bf-asm/proxy_hash.cpp
@@ -172,7 +172,8 @@ void ProxyHashMatchTable::gen_tbl_cfg(json::vector &out) const {
             BUG_CHECK(fmt_width, "width of format is 0");
             way_tbl["size"] = way.rams.size() / fmt_width * format->groups() * 1024;
             add_pack_format(way_tbl, format.get(), false);
-            way_tbl["memory_resource_allocation"] = gen_memory_resource_allocation_tbl_cfg(way);
+            way_tbl["memory_resource_allocation"] =
+                gen_memory_resource_allocation_tbl_cfg_with_way(way);
             way_stage_tables.push_back(std::move(way_tbl));
         }
     }

diff --git a/backends/tofino/bf-asm/sram_match.cpp b/backends/tofino/bf-asm/sram_match.cpp
@@ -338,7 +338,7 @@ bool SRamMatchTable::verify_match_key() {
     return error_count == 0;
 }
 
-std::unique_ptr<json::map> SRamMatchTable::gen_memory_resource_allocation_tbl_cfg(
+std::unique_ptr<json::map> SRamMatchTable::gen_memory_resource_allocation_tbl_cfg_with_way(
     const Way &way) const {
     json::map mra;
     unsigned vpn_ctr = 0;

diff --git a/backends/tofino/bf-asm/tables.cpp b/backends/tofino/bf-asm/tables.cpp
@@ -22,6 +22,7 @@
 
 #include "action_bus.h"
 #include "backends/tofino/bf-asm/config.h"
+#include "backends/tofino/bf-asm/json.h"
 #include "backends/tofino/bf-asm/stage.h"
 #include "input_xbar.h"
 #include "instruction.h"
@@ -2304,7 +2305,7 @@ void Table::Actions::Action::check_and_add_resource(json::vector &resources,
     // present in the resource array
     bool found = false;
     for (auto &r : resources) {
-        if (resource == r->to<json::map>()) {
+        if (resource == r->to<json::obj>()) {
             found = true;
             break;
         }
@@ -2556,7 +2557,7 @@ void Table::Actions::add_action_format(const Table *table, json::map &tbl) const
             json::string name = a.first;
             int lo = remove_name_tail_range(name);
             json::string immed_name = a.second.name;
-            if (immed_name != "immediate") continue;  // output only immediate fields
+            if (immed_name != json::string("immediate")) continue;  // output only immediate fields
             if (!(act.has_param(name) || a.second.is_constant))
                 continue;  // and fields that are parameters or constants
             json::map action_format_per_action_imm_field;

diff --git a/backends/tofino/bf-asm/tables.h b/backends/tofino/bf-asm/tables.h
@@ -214,11 +214,11 @@ class Table {
         operator bool() const { return all && all->count(name) > 0; }
         operator Table *() const { return ::get(all, name); }
         Table *operator->() const { return ::get(all, name); }
-        bool set() const { return lineno >= 0; }
-        bool operator==(const Table *t) const { return name == t->name_; }
-        bool operator==(const char *t) const { return name == t; }
-        bool operator==(const std::string &t) const { return name == t; }
+        [[nodiscard]] bool set() const { return lineno >= 0; }
+        bool operator==(const Table &t) const { return name == t.name_; }
+        bool operator!=(const Table &t) const { return name != t.name_; }
         bool operator==(const Ref &a) const { return name == a.name; }
+        bool operator!=(const Ref &a) const { return name != a.name; }
         bool operator<(const Ref &a) const { return name < a.name; }
         bool check() const {
             if (set() && !*this) error(lineno, "No table named %s", name.c_str());
@@ -1320,7 +1320,7 @@ DECLARE_ABSTRACT_TABLE_TYPE(SRamMatchTable, MatchTable,         // exact, atcam,
     void add_field_to_pack_format(json::vector &field_list, unsigned basebit, std::string name,
                                   const Table::Format::Field &field,
                                   const Table::Actions::Action *act) const override;
-    std::unique_ptr<json::map> gen_memory_resource_allocation_tbl_cfg(const Way &) const;
+    std::unique_ptr<json::map> gen_memory_resource_allocation_tbl_cfg_with_way(const Way &) const;
     Actions *get_actions() const override {
         return actions ? actions.get() : (action ? action->actions.get() : nullptr);
     }
@@ -1412,7 +1412,7 @@ DECLARE_TABLE_TYPE(
     void verify_format(Target::Tofino) override;
     void verify_entry_priority(); void setup_column_priority(); void find_tcam_match();
     void gen_unit_cfg(json::vector &units, int size) const;
-    std::unique_ptr<json::vector> gen_memory_resource_allocation_tbl_cfg() const;
+    std::unique_ptr<json::vector> gen_memory_resource_allocation_tbl_cfg_no_input() const;
     void setup_nibble_mask(Table::Format::Field *match, int group,
                            std::map<int, match_element> &elems, bitvec &mask);
     std::string get_match_mode(const Phv::Ref &pref, int offset) const override;

diff --git a/backends/tofino/bf-p4c/common/extract_maupipe.cpp b/backends/tofino/bf-p4c/common/extract_maupipe.cpp
@@ -322,7 +322,7 @@ class SetupActionProperties : public MauModifier {
             if (!path) BUG("Default action path %s cannot be found", default_action);
             auto actName = refMap->getDeclaration(path->path, true)->externalName();
 
-            if (actName == act->name) {
+            if (act->name == actName) {
                 is_the_default_action = true;
                 if (has_constant_default_action) {
                     can_be_default_action = true;  // this is the constant default action

diff --git a/backends/tofino/bf-p4c/mau/asm_output.cpp b/backends/tofino/bf-p4c/mau/asm_output.cpp
@@ -2305,7 +2305,7 @@ void MauAsmOutput::emit_static_entries(std::ostream &, indent_t indent, const IR
         auto method = method_call->method->to<IR::PathExpression>();
         auto path = method->path;
         for (auto action : Values(tbl->actions)) {
-            if (action->name.name == path->name) {
+            if (path->name == action->name.name) {
                 context_json_entries << indent << "action_handle: 0x" << hex(action->handle)
                                      << std::endl;
                 break;

diff --git a/backends/tofino/bf-p4c/mau/gateway.cpp b/backends/tofino/bf-p4c/mau/gateway.cpp
@@ -160,7 +160,7 @@ const IR::Expression *CanonGatewayExpr::postorder(IR::Operation::Relation *e) {
     Pattern::Match<IR::Expression> e1, e2;
     Pattern::Match<IR::Constant> k1, k2;
     int width = safe_width_bits(e->left->type);
-    if (((e1 & k1) == k2).match(e) || ((e1 & k1) != k2).match(e)) {
+    if ((k2 == (e1 & k1)).match(e) || (k2 != (e1 & k1)).match(e)) {
         BUG_CHECK(!e1->is<IR::Constant>(), "constant folding failed");
         // always true or always false
         if ((abs(k1->value) & abs(k2->value)) != abs(k2->value)) {

diff --git a/backends/tofino/bf-p4c/mau/instruction_selection.cpp b/backends/tofino/bf-p4c/mau/instruction_selection.cpp
@@ -3111,7 +3111,7 @@ const IR::Node *RemoveUnnecessaryActionArgSlice::preorder(IR::Slice *sl) {
 // Simplify "actionArg != 0 ? f0 : f1" to "actionArg ? f0 : f1"
 const IR::Node *SimplifyConditionalActionArg::postorder(IR::Mux *mux) {
     Pattern::Match<IR::MAU::ActionArg> aa;
-    if ((0 != aa).match(mux->e0)) mux->e0 = aa;
+    if ((aa != 0).match(mux->e0)) mux->e0 = aa;
     return mux;
 }
 

diff --git a/backends/tofino/bf-p4c/mau/stateful_alu.cpp b/backends/tofino/bf-p4c/mau/stateful_alu.cpp
@@ -1328,7 +1328,7 @@ bool CreateSaluInstruction::preorder(const IR::Operation::Relation *rel, cstring
     if (etype == IF) {
         Pattern::Match<IR::Expression> e1, e2;
         Pattern::Match<IR::Constant> k;
-        if (Device::statefulAluSpec().CmpMask && ((e1 & k) == e2).match(rel) && !k->fitsUint() &&
+        if (Device::statefulAluSpec().CmpMask && (e2 == (e1 & k)).match(rel) && !k->fitsUint() &&
             !k->fitsInt()) {
             // FIXME -- wide "neq" can be done with tmatch too?
             opcode = "tmatch"_cs;

diff --git a/backends/tofino/bf-p4c/midend/check_unsupported.cpp b/backends/tofino/bf-p4c/midend/check_unsupported.cpp
@@ -69,13 +69,13 @@ void CheckUnsupported::postorder(const IR::P4Table *const table_ptr) {
         size_t total_TCAM_key_bits = 0u;
 
         for (const auto *const key_element_ptr : key_ptr->keyElements) {
-            if ("lpm" == key_element_ptr->matchType->path->name) {
+            if (key_element_ptr->matchType->path->name == "lpm") {
                 ++lpm_key_count;
             }
-            if ("range" == key_element_ptr->matchType->path->name) {
+            if (key_element_ptr->matchType->path->name == "range") {
                 ++range_key_count;
             }
-            if ("ternary" == key_element_ptr->matchType->path->name) {
            if (key_element_ptr->matchType->path->name == "ternary") {
                 ++ternary_key_count;
                 const size_t size = table_ptr->getSizeProperty()->asUint64(),
                              this_TCAM_key_bits =

diff --git a/backends/tofino/bf-p4c/parde/extract_parser.cpp b/backends/tofino/bf-p4c/parde/extract_parser.cpp
@@ -90,7 +90,7 @@ struct GetHeaderStackIndex : public Inspector {
                 BUG_CHECK(hdr, "%1%: not a header reference in extract", statement);
 
                 if (!hdr->is<IR::HeaderStackItemRef>()) {
-                    if (header == hdr->to<IR::ConcreteHeaderRef>()->ref->name) {
+                    if (hdr->to<IR::ConcreteHeaderRef>()->ref->name == header) {
                         rv = 0;
                     }
                 }
@@ -553,7 +553,7 @@ const IR::BFN::Parser *GetBackendParser::createBackendParser() {
         while (bitr != binfo->end()) {
             auto b = *bitr;
             auto bparser = b.first->to<IR::P4Parser>();
-            if (bparser && (bparser->name.originalName == parser->name) &&
+            if (bparser && (parser->name.name == bparser->name.originalName) &&
                 (b.second.gress == parser->thread)) {
                 if (!b.second.parser_instance_name.isNullOrEmpty())
                     multiParserName = b.second.parser_instance_name;

diff --git a/backends/tofino/bf-p4c/parde/lowered/hoist_common_match_operations.cpp b/backends/tofino/bf-p4c/parde/lowered/hoist_common_match_operations.cpp
@@ -329,11 +329,15 @@ bool HoistCommonMatchOperations::can_hoist(const IR::BFN::LoweredParserMatch *a,
 
     auto extactors_required = extractors_used(a);
     auto b_extractors = extractors_used(b);
-    extactors_required = std::accumulate(b_extractors.begin(), b_extractors.end(),
-                                         extactors_required, [](auto &map, const auto &pair) {
-                                             map[pair.first] += pair.second;
-                                             return map;
-                                         });
+    // then default-constructs value (0 for uint), then += works.
+    extactors_required =
+        std::accumulate(b_extractors.begin(), b_extractors.end(), std::move(extactors_required),
+                        [](std::map<unsigned int, unsigned int> current_map,
+                           const std::pair<const unsigned int, unsigned int> &pair) {
+                            current_map[pair.first] += pair.second;
+                            return current_map;
+                        });
+
     for (const auto &[size, max] : Device::pardeSpec().extractorSpec())
         if (extactors_required[size] > max) return false;
 

diff --git a/backends/tofino/bf-p4c/phv/utils/utils.h b/backends/tofino/bf-p4c/phv/utils/utils.h
@@ -160,7 +160,7 @@ class Allocation {
         ConditionalConstraintData()
             : bitPosition(-1), rotationAllowed(false), container(std::nullopt) {}
 
-        bool operator==(ConditionalConstraintData &other) const {
+        bool operator==(const ConditionalConstraintData &other) const {
             return bitPosition == other.bitPosition && rotationAllowed == other.rotationAllowed &&
                    container == other.container;
         }

diff --git a/backends/tofino/bf-p4c/phv/v2/utils_v2.h b/backends/tofino/bf-p4c/phv/v2/utils_v2.h
@@ -197,9 +197,6 @@ class ScoreContext {
     /// search time related parameters.
     const SearchConfig *search_config_i = new SearchConfig();
 
-    /// tracer will try to log steps of every allocation.
-    std::ostream *tracer = nullptr;
-
  private:
     static constexpr const char *tab_table[] = {
         "", " ", "  ", "   ", "    ", "     ", "      ", "       ", "        ",

diff --git a/bazel/example/.bazelrc b/bazel/example/.bazelrc
@@ -3,9 +3,9 @@ common --enable_workspace
 # Enable once #5066 is resolved.
 common --noenable_bzlmod
 
-# Use C++17.
-build --cxxopt=-std=c++17
-build --host_cxxopt=-std=c++17
+# Use C++20.
+build --cxxopt=-std=c++20
+build --host_cxxopt=-std=c++20
 
 # Force the use of Clang for all builds.
 build --action_env=CC=clang

diff --git a/docs/C++.md b/docs/C++.md
@@ -1,4 +1,4 @@
-C++ (following the C++ 11 standard) is the implementation language for
+C++ (following the C++ 20 standard) is the implementation language for
 the compiler.  This file contains notes on how we use C++ and conventions
 we use for things that C++ does not handle well.
 

diff --git a/ir/pattern.h b/ir/pattern.h
@@ -183,6 +183,22 @@ class Pattern {
     Pattern operator||(const Pattern &r) const {
         return Pattern(new Binary<IR::LOr>(pattern, r.pattern));
     }
+    /// We use these templates to deal with amgigous overloads introduced by C++20.
+    /// https://en.cppreference.com/w/cpp/language/default_comparisons
+    // TODO: Ideally, we would fix these ambiguous overloads by making the Pattern class explicit in
+    // its initialization but that is a breaking change.
+    template <class T>
+    Pattern operator==(Match<T> &m) const {
+        return *this == Pattern(m);
+    }
+    template <class T>
+    Pattern operator!=(Match<T> &m) const {
+        return *this != Pattern(m);
+    }
+    template <class T>
+    Pattern operator==(const Match<T> &m) const {
+        return *this == Pattern(m);
+    }
 
     bool match(const IR::Node *n) { return pattern->match(n); }
 };