8317837: Leftover FFM implementation-only changes

Co-authored-by: Maurizio Cimadamore <mcimadamore@openjdk.org>
Co-authored-by: Per Minborg <pminborg@openjdk.org>
Reviewed-by: mcimadamore

src/java.base/share/classes/java/lang/String.java

@@ -28,6 +28,8 @@ package java.lang;
 import java.io.ObjectStreamField;
 import java.io.UnsupportedEncodingException;
 import java.lang.annotation.Native;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.ValueLayout;
 import java.lang.invoke.MethodHandles;
 import java.lang.constant.Constable;
 import java.lang.constant.ConstantDesc;
@@ -1836,6 +1838,21 @@ public final class String
         return encode(Charset.defaultCharset(), coder(), value);
     }
 
+    boolean bytesCompatible(Charset charset) {
+        if (isLatin1()) {
+            if (charset == ISO_8859_1.INSTANCE) {
+                return true; // ok, same encoding
+            } else if (charset == UTF_8.INSTANCE || charset == US_ASCII.INSTANCE) {
+                return !StringCoding.hasNegatives(value, 0, value.length); // ok, if ASCII-compatible
+            }
+        }
+        return false;
+    }
+
+    void copyToSegmentRaw(MemorySegment segment, long offset) {
+        MemorySegment.copy(value, 0, segment, ValueLayout.JAVA_BYTE, offset, value.length);
+    }
+
     /**
      * Compares this string to the specified object.  The result is {@code
      * true} if and only if the argument is not {@code null} and is a {@code

src/java.base/share/classes/java/lang/System.java

@@ -35,6 +35,7 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.PrintStream;
 import java.lang.annotation.Annotation;
+import java.lang.foreign.MemorySegment;
 import java.lang.invoke.MethodHandle;
 import java.lang.invoke.MethodType;
 import java.lang.invoke.StringConcatFactory;
@@ -88,7 +89,6 @@ import jdk.internal.vm.Continuation;
 import jdk.internal.vm.ContinuationScope;
 import jdk.internal.vm.StackableScope;
 import jdk.internal.vm.ThreadContainer;
-import jdk.internal.vm.annotation.ForceInline;
 import jdk.internal.vm.annotation.IntrinsicCandidate;
 import jdk.internal.vm.annotation.Stable;
 import sun.nio.fs.DefaultFileSystemProvider;
@@ -2669,6 +2669,16 @@ public final class System {
             public String getLoaderNameID(ClassLoader loader) {
                 return loader.nameAndId();
             }
+
+            @Override
+            public void copyToSegmentRaw(String string, MemorySegment segment, long offset) {
+                string.copyToSegmentRaw(segment, offset);
+            }
+
+            @Override
+            public boolean bytesCompatible(String string, Charset charset) {
+                return string.bytesCompatible(charset);
+            }
         });
     }
 }

src/java.base/share/classes/java/lang/foreign/MemorySegment.java

@@ -1076,7 +1076,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
      * such that {@code isAccessibleBy(T) == false}.
      */
     default String getString(long offset) {
-        return getString(offset, StandardCharsets.UTF_8);
+        return getString(offset, sun.nio.cs.UTF_8.INSTANCE);
     }
 
     /**
@@ -1132,7 +1132,7 @@ public sealed interface MemorySegment permits AbstractMemorySegmentImpl {
      */
     default void setString(long offset, String str) {
         Objects.requireNonNull(str);
-        setString(offset, str, StandardCharsets.UTF_8);
+        setString(offset, str, sun.nio.cs.UTF_8.INSTANCE);
     }
 
     /**

src/java.base/share/classes/java/lang/foreign/SegmentAllocator.java

@@ -89,7 +89,7 @@ public interface SegmentAllocator {
     @ForceInline
     default MemorySegment allocateFrom(String str) {
         Objects.requireNonNull(str);
-        return allocateFrom(str, StandardCharsets.UTF_8);
+        return allocateFrom(str, sun.nio.cs.UTF_8.INSTANCE);
     }
 
     /**
@@ -124,11 +124,20 @@ public interface SegmentAllocator {
         Objects.requireNonNull(charset);
         Objects.requireNonNull(str);
         int termCharSize = StringSupport.CharsetKind.of(charset).terminatorCharSize();
-        byte[] bytes = str.getBytes(charset);
-        MemorySegment segment = allocateNoInit(bytes.length + termCharSize);
-        MemorySegment.copy(bytes, 0, segment, ValueLayout.JAVA_BYTE, 0, bytes.length);
+        MemorySegment segment;
+        int length;
+        if (StringSupport.bytesCompatible(str, charset)) {
+            length = str.length();
+            segment = allocateNoInit((long) length + termCharSize);
+            StringSupport.copyToSegmentRaw(str, segment, 0);
+        } else {
+            byte[] bytes = str.getBytes(charset);
+            length = bytes.length;
+            segment = allocateNoInit((long) bytes.length + termCharSize);
+            MemorySegment.copy(bytes, 0, segment, ValueLayout.JAVA_BYTE, 0, bytes.length);
+        }
         for (int i = 0 ; i < termCharSize ; i++) {
-            segment.set(ValueLayout.JAVA_BYTE, bytes.length + i, (byte)0);
+            segment.set(ValueLayout.JAVA_BYTE, length + i, (byte)0);
         }
         return segment;
     }

src/java.base/share/classes/java/lang/invoke/VarHandleSegmentViewBase.java

@@ -25,6 +25,8 @@
 
 package java.lang.invoke;
 
+import jdk.internal.foreign.Utils;
+
 /**
  * Base class for memory segment var handle view implementations.
  */
@@ -54,7 +56,7 @@ abstract sealed class VarHandleSegmentViewBase extends VarHandle permits
     }
 
     static IllegalArgumentException newIllegalArgumentExceptionForMisalignedAccess(long address) {
-        return new IllegalArgumentException("Misaligned access at address: " + address);
+        return new IllegalArgumentException("Misaligned access at address: " + Utils.toHexString(address));
     }
 
     static UnsupportedOperationException newUnsupportedAccessModeForAlignment(long alignment) {