feat: add simple key-value store to the builders

frontend/cs/r1cs/builder.go

@@ -29,6 +29,7 @@ import (
 	"github.com/consensys/gnark/frontend"
 	"github.com/consensys/gnark/frontend/internal/expr"
 	"github.com/consensys/gnark/frontend/schema"
+	"github.com/consensys/gnark/internal/kvstore"
 	"github.com/consensys/gnark/internal/tinyfield"
 	"github.com/consensys/gnark/internal/utils"
 	"github.com/consensys/gnark/logger"
@@ -63,6 +64,8 @@ type builder struct {
 	// buffers used to do in place api.MAC
 	mbuf1 expr.LinearExpression
 	mbuf2 expr.LinearExpression
+
+	kvstore.Store
 }
 
 // initialCapacity has quite some impact on frontend performance, especially on large circuits size
@@ -78,6 +81,7 @@ func newBuilder(field *big.Int, config frontend.CompileConfig) *builder {
 		heap:       make(minHeap, 0, 100),
 		mbuf1:      make(expr.LinearExpression, 0, macCapacity),
 		mbuf2:      make(expr.LinearExpression, 0, macCapacity),
+		Store:      kvstore.New(),
 	}
 
 	// by default the circuit is given a public wire equal to 1

frontend/cs/scs/builder.go

@@ -29,6 +29,7 @@ import (
 	"github.com/consensys/gnark/frontend/cs"
 	"github.com/consensys/gnark/frontend/internal/expr"
 	"github.com/consensys/gnark/frontend/schema"
+	"github.com/consensys/gnark/internal/kvstore"
 	"github.com/consensys/gnark/internal/tinyfield"
 	"github.com/consensys/gnark/internal/utils"
 	"github.com/consensys/gnark/logger"
@@ -57,6 +58,8 @@ type scs struct {
 	mtBooleans map[int]struct{}
 
 	q *big.Int
+
+	kvstore.Store
 }
 
 // initialCapacity has quite some impact on frontend performance, especially on large circuits size
@@ -67,6 +70,7 @@ func newBuilder(field *big.Int, config frontend.CompileConfig) *scs {
 		mtBooleans: make(map[int]struct{}),
 		st:         cs.NewCoeffTable(),
 		config:     config,
+		Store:      kvstore.New(),
 	}
 
 	curve := utils.FieldToCurve(field)

internal/kvstore/kvstore.go

@@ -0,0 +1,38 @@
+// Package kvstore implements simple key-value store
+//
+// It is without synchronization and allows any comparable keys. The main use of
+// this package is for sharing singletons when building a circuit.
+package kvstore
+
+import (
+	"reflect"
+)
+
+type Store interface {
+	SetKeyValue(key, value any)
+	GetKeyValue(key any) (value any)
+}
+
+type impl struct {
+	db map[any]any
+}
+
+func New() Store {
+	return &impl{
+		db: make(map[any]any),
+	}
+}
+
+func (c *impl) SetKeyValue(key, value any) {
+	if !reflect.TypeOf(key).Comparable() {
+		panic("key type not comparable")
+	}
+	c.db[key] = value
+}
+
+func (c *impl) GetKeyValue(key any) any {
+	if !reflect.TypeOf(key).Comparable() {
+		panic("key type not comparable")
+	}
+	return c.db[key]
+}

test/engine.go

@@ -34,6 +34,7 @@ import (
 	"github.com/consensys/gnark/backend"
 	"github.com/consensys/gnark/backend/hint"
 	"github.com/consensys/gnark/frontend"
+	"github.com/consensys/gnark/internal/kvstore"
 	"github.com/consensys/gnark/internal/utils"
 )
 
@@ -50,6 +51,7 @@ type engine struct {
 	// mHintsFunctions map[hint.ID]hintFunction
 	constVars  bool
 	apiWrapper ApiWrapper
+	kvstore.Store
 }
 
 // TestEngineOption defines an option for the test engine.
@@ -103,6 +105,7 @@ func IsSolved(circuit, witness frontend.Circuit, field *big.Int, opts ...TestEng
 		q:          new(big.Int).Set(field),
 		apiWrapper: func(a frontend.API) frontend.API { return a },
 		constVars:  false,
+		Store:      kvstore.New(),
 	}
 	for _, opt := range opts {
 		if err := opt(e); err != nil {

test/solver_test.go

@@ -18,6 +18,7 @@ import (
 	"github.com/consensys/gnark/frontend/cs/scs"
 	"github.com/consensys/gnark/frontend/schema"
 	"github.com/consensys/gnark/internal/backend/circuits"
+	"github.com/consensys/gnark/internal/kvstore"
 	"github.com/consensys/gnark/internal/tinyfield"
 	"github.com/consensys/gnark/internal/utils"
 )
@@ -155,6 +156,7 @@ func isSolvedEngine(c frontend.Circuit, field *big.Int, opts ...TestEngineOption
 		q:          new(big.Int).Set(field),
 		apiWrapper: func(a frontend.API) frontend.API { return a },
 		constVars:  false,
+		Store:      kvstore.New(),
 	}
 	for _, opt := range opts {
 		if err := opt(e); err != nil {