[JVM] Micro-optimize method signature mapping

This commit optimizes functions related to method signature mapping on
the JVM backend. The most significant change is avoiding re-allocations
in StringBuilder when building internal names. The commit also includes
minor optimizations, such as removing redundant allocations of strings
and other objects.

core/compiler.common.jvm/src/org/jetbrains/kotlin/load/java/SpecialGenericSignatures.kt

@@ -134,7 +134,7 @@ open class SpecialGenericSignatures {
                 signatureAndName.copy(name = jdkName).signature
             }
 
-        val ORIGINAL_SHORT_NAMES: List<Name> = NAME_AND_SIGNATURE_TO_JVM_REPRESENTATION_NAME_MAP.keys.map { it.name }
+        val ORIGINAL_SHORT_NAMES: Set<Name> = NAME_AND_SIGNATURE_TO_JVM_REPRESENTATION_NAME_MAP.keys.mapTo(HashSet()) { it.name }
 
         val JVM_SHORT_NAME_TO_BUILTIN_SHORT_NAMES_MAP: Map<Name, Name> =
             NAME_AND_SIGNATURE_TO_JVM_REPRESENTATION_NAME_MAP.entries

core/compiler.common.jvm/src/org/jetbrains/kotlin/load/kotlin/SignatureBuildingComponents.kt

@@ -34,5 +34,5 @@ object SignatureBuildingComponents {
 
 val ClassId.internalName: String
     get() {
-        return JvmClassName.byClassId(JavaToKotlinClassMap.mapKotlinToJava(asSingleFqName().toUnsafe()) ?: this).internalName
+        return JvmClassName.internalNameByClassId(JavaToKotlinClassMap.mapKotlinToJava(asSingleFqName().toUnsafe()) ?: this)
     }

core/compiler.common.jvm/src/org/jetbrains/kotlin/load/kotlin/typeSignatureMapping.kt

@@ -55,7 +55,7 @@ fun <T : Any> TypeSystemCommonBackendContext.mapBuiltInType(
             if (!mode.kotlinCollectionsToJavaCollections && JavaToKotlinClassMap.mutabilityMappings.any { it.javaClass == classId })
                 return null
 
-            return typeFactory.createObjectType(JvmClassName.byClassId(classId).internalName)
+            return typeFactory.createObjectType(JvmClassName.internalNameByClassId(classId))
         }
     }
 

core/compiler.common.jvm/src/org/jetbrains/kotlin/resolve/jvm/JvmClassName.java

@@ -28,11 +28,16 @@ public class JvmClassName {
 
     @NotNull
     public static JvmClassName byClassId(@NotNull ClassId classId) {
+        return new JvmClassName(internalNameByClassId(classId));
+    }
+
+    @NotNull
+    public static String internalNameByClassId(@NotNull ClassId classId) {
         FqName packageFqName = classId.getPackageFqName();
         String relativeClassName = classId.getRelativeClassName().asString().replace('.', '$');
         return packageFqName.isRoot()
-               ? new JvmClassName(relativeClassName)
-               : new JvmClassName(packageFqName.asString().replace('.', '/') + "/" + relativeClassName);
+               ? relativeClassName
+               : packageFqName.asString().replace('.', '/') + "/" + relativeClassName;
     }
 
     /**

core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/methodSignatureMapping.kt

@@ -93,7 +93,7 @@ internal fun CallableDescriptor.computeJvmSignature(): String? = signatures {
 internal val ClassDescriptor.internalName: String
     get() {
         JavaToKotlinClassMap.mapKotlinToJava(fqNameSafe.toUnsafe())?.let {
-            return JvmClassName.byClassId(it).internalName
+            return JvmClassName.internalNameByClassId(it)
         }
 
         return computeInternalName(this)

core/util.runtime/src/org/jetbrains/kotlin/utils/capitalizeDecapitalize.kt

@@ -109,7 +109,10 @@ fun String.capitalizeAsciiOnly(): String {
     if (isEmpty()) return this
     val c = this[0]
     return if (c in 'a'..'z')
-        c.uppercaseChar() + substring(1)
+        buildString(length) {
+            append(c.uppercaseChar())
+            append(this@capitalizeAsciiOnly, 1, this@capitalizeAsciiOnly.length)
+        }
     else
         this
 }