Cache generic signature instantiations

Author: ahejlsberg

src/compiler/checker.ts

@@ -4232,7 +4232,7 @@ namespace ts {
             for (const baseSig of baseSignatures) {
                 const typeParamCount = baseSig.typeParameters ? baseSig.typeParameters.length : 0;
                 if (typeParamCount === typeArgCount) {
-                    const sig = typeParamCount ? getSignatureInstantiation(baseSig, typeArguments) : cloneSignature(baseSig);
+                    const sig = typeParamCount ? createSignatureInstantiation(baseSig, typeArguments) : cloneSignature(baseSig);
                     sig.typeParameters = classType.localTypeParameters;
                     sig.resolvedReturnType = classType;
                     result.push(sig);
@@ -4982,6 +4982,12 @@ namespace ts {
         }
 
         function getSignatureInstantiation(signature: Signature, typeArguments: Type[]): Signature {
+            const instantiations = signature.instantiations || (signature.instantiations = createMap<Signature>());
+            const id = getTypeListId(typeArguments);
+            return instantiations[id] || (instantiations[id] = createSignatureInstantiation(signature, typeArguments));
+        }
+
+        function createSignatureInstantiation(signature: Signature, typeArguments: Type[]): Signature {
             return instantiateSignature(signature, createTypeMapper(signature.typeParameters, typeArguments), /*eraseTypeParameters*/ true);
         }
 

src/compiler/types.ts

@@ -2923,6 +2923,8 @@ namespace ts {
         isolatedSignatureType?: ObjectType; // A manufactured type that just contains the signature for purposes of signature comparison
         /* @internal */
         typePredicate?: TypePredicate;
+        /* @internal */
+        instantiations?: Map<Signature>;    // Generic signature instantiation cache
     }
 
     export const enum IndexKind {