Do not make the RubyString native when passed to a :string argument of a FFI call

* See #3293 (comment)
  and ffi/ffi#1080
* As that could cause extra conversions to managed later on.

Author: eregon

CHANGELOG.md

@@ -64,6 +64,7 @@ Performance:
 * Change the `Hash` representation from traditional buckets to a "compact hash table" for improved locality, performance and memory footprint (#3172, @moste00).
 * Optimize calls with `ruby2_keywords` forwarding by deciding it per call site instead of per callee thanks to [my fix in CRuby 3.2](https://bugs.ruby-lang.org/issues/18625) (@eregon).
 * Optimize feature loading when require is called with an absolute path to a .rb file (@rwstauner).
+* Avoid extra copies for Strings passed as `:string` arguments to a FFI call and used later for Regexp matching (#3293, @eregon).
 
 Changes:
 

lib/truffle/truffle/ffi_backend/function.rb

@@ -155,7 +155,7 @@ def free
         get_pointer_value(value)
       elsif FFI::Type::STRING == type
         Truffle::Type.check_null_safe(value) unless Primitive.nil?(value)
-        get_pointer_value(value)
+        Truffle::CExt.string_to_ffi_pointer_copy(value)
       elsif Primitive.is_a?(type, FFI::FunctionType) and Primitive.is_a?(value, Proc)
         callback(value, type)
       else
@@ -198,7 +198,7 @@ def free
       elsif Primitive.nil?(value)
         Truffle::FFI::Pointer::NULL
       elsif Primitive.is_a?(value, String)
-        Truffle::CExt.string_to_ffi_pointer(value)
+        Truffle::CExt.string_to_ffi_pointer_inplace(value)
       elsif value.respond_to?(:to_ptr)
         Truffle::Type.coerce_to value, Truffle::FFI::Pointer, :to_ptr
       else

lib/truffle/truffle/fiddle_backend.rb

@@ -93,7 +93,8 @@ def self.convert_ruby_to_native(type, val)
 
   def self.get_pointer_value(val)
     if Primitive.is_a?(val, String)
-      Truffle::CExt.string_to_ffi_pointer(val)
+      # NOTE: Fiddle::TYPE_CONST_STRING wouldn't need inplace, but not defined yet by this file
+      Truffle::CExt.string_to_ffi_pointer_inplace(val)
     elsif Primitive.is_a?(val, Fiddle::Pointer)
       val.to_i
     elsif val.respond_to?(:to_ptr)

src/main/java/org/truffleruby/cext/CExtNodes.java

@@ -13,6 +13,7 @@
 import java.util.Arrays;
 import java.util.concurrent.locks.ReentrantLock;
 
+import com.oracle.truffle.api.CompilerAsserts;
 import com.oracle.truffle.api.TruffleSafepoint;
 import com.oracle.truffle.api.dsl.Bind;
 import com.oracle.truffle.api.dsl.GenerateCached;
@@ -714,7 +715,7 @@ public abstract static class RbEncCodeRangeClear extends CoreMethodArrayArgument
         @Specialization
         RubyString clearCodeRange(RubyString string,
                 @Cached StringToNativeNode stringToNativeNode) {
-            stringToNativeNode.executeToNative(this, string);
+            stringToNativeNode.executeToNative(this, string, true);
             string.clearCodeRange();
 
             return string;
@@ -817,7 +818,7 @@ public abstract static class RbStrCapacityNode extends CoreMethodArrayArgumentsN
         @Specialization
         long capacity(Object string,
                 @Cached StringToNativeNode stringToNativeNode) {
-            return getNativeStringCapacity(stringToNativeNode.executeToNative(this, string));
+            return getNativeStringCapacity(stringToNativeNode.executeToNative(this, string, true));
         }
     }
 
@@ -830,7 +831,7 @@ RubyString strSetLen(RubyString string, int newByteLength,
                 @Cached StringToNativeNode stringToNativeNode,
                 @Cached MutableTruffleString.FromNativePointerNode fromNativePointerNode,
                 @Cached InlinedConditionProfile minLengthOneProfile) {
-            var pointer = stringToNativeNode.executeToNative(this, string);
+            var pointer = stringToNativeNode.executeToNative(this, string, true);
 
             var encoding = libString.getEncoding(string);
             int minLength = encoding.jcoding.minLength();
@@ -860,7 +861,7 @@ RubyString rbStrResize(RubyString string, int newByteLength,
                 @Cached RubyStringLibrary libString,
                 @Cached StringToNativeNode stringToNativeNode,
                 @Cached MutableTruffleString.FromNativePointerNode fromNativePointerNode) {
-            var pointer = stringToNativeNode.executeToNative(this, string);
+            var pointer = stringToNativeNode.executeToNative(this, string, true);
             var tencoding = libString.getTEncoding(string);
             int byteLength = string.tstring.byteLength(tencoding);
 
@@ -889,7 +890,7 @@ RubyString trStrCapaResize(RubyString string, int newCapacity,
                 @Cached RubyStringLibrary libString,
                 @Cached StringToNativeNode stringToNativeNode,
                 @Cached MutableTruffleString.FromNativePointerNode fromNativePointerNode) {
-            var pointer = stringToNativeNode.executeToNative(this, string);
+            var pointer = stringToNativeNode.executeToNative(this, string, true);
             var tencoding = libString.getTEncoding(string);
 
             if (getNativeStringCapacity(pointer) == newCapacity) {
@@ -1327,24 +1328,29 @@ int rbHash(Object object,
         }
     }
 
+    /** If inplace is true, this node mutates the RubyString to use native memory. It should be avoided unless there is
+     * no other way because e.g. Regexp matching later on that String would then copy to managed byte[] back, and
+     * copying back-and-forth is quite expensive. OTOH if the String will need to be used as native memory again soon
+     * after and without needing to go to managed in between then it is valuable to avoid extra copies. */
     @GenerateInline
     @GenerateCached(false)
     public abstract static class StringToNativeNode extends RubyBaseNode {
 
-        public abstract Pointer executeToNative(Node node, Object string);
+        public abstract Pointer executeToNative(Node node, Object string, boolean inplace);
 
         @Specialization
-        static Pointer toNative(Node node, RubyString string,
+        static Pointer toNative(Node node, RubyString string, boolean inplace,
                 @Cached RubyStringLibrary libString,
                 @Cached InlinedConditionProfile convertProfile,
                 @Cached(inline = false) TruffleString.CopyToNativeMemoryNode copyToNativeMemoryNode,
                 @Cached(inline = false) MutableTruffleString.FromNativePointerNode fromNativePointerNode,
                 @Cached(inline = false) TruffleString.GetInternalNativePointerNode getInternalNativePointerNode) {
+            CompilerAsserts.partialEvaluationConstant(inplace);
+
             var tstring = string.tstring;
             var tencoding = libString.getTEncoding(string);
 
             final Pointer pointer;
-
             if (convertProfile.profile(node, tstring.isNative())) {
                 assert tstring.isMutable();
                 pointer = (Pointer) getInternalNativePointerNode.execute(tstring, tencoding);
@@ -1353,16 +1359,18 @@ static Pointer toNative(Node node, RubyString string,
                 pointer = allocateAndCopyToNative(getLanguage(node), getContext(node), tstring, tencoding, byteLength,
                         copyToNativeMemoryNode);
 
-                var nativeTString = fromNativePointerNode.execute(pointer, 0, byteLength, tencoding, false);
-                string.setTString(nativeTString);
+                if (inplace) {
+                    var nativeTString = fromNativePointerNode.execute(pointer, 0, byteLength, tencoding, false);
+                    string.setTString(nativeTString);
+                }
             }
 
             return pointer;
         }
 
         @Specialization
-        static Pointer toNativeImmutable(Node node, ImmutableRubyString string) {
-            return string.getNativeString(getLanguage(node));
+        static Pointer toNativeImmutable(Node node, ImmutableRubyString string, boolean inplace) {
+            return string.getNativeString(getLanguage(node), getContext(node));
         }
 
         public static Pointer allocateAndCopyToNative(RubyLanguage language, RubyContext context,
@@ -1381,17 +1389,34 @@ public abstract static class StringPointerToNativeNode extends PrimitiveArrayArg
         @Specialization
         long toNative(Object string,
                 @Cached StringToNativeNode stringToNativeNode) {
-            return stringToNativeNode.executeToNative(this, string).getAddress();
+            return stringToNativeNode.executeToNative(this, string, true).getAddress();
+        }
+    }
+
+    @CoreMethod(names = "string_to_ffi_pointer_inplace", onSingleton = true, required = 1)
+    public abstract static class StringToFFIPointerInplaceNode extends CoreMethodArrayArgumentsNode {
+
+        @Specialization
+        RubyPointer toFFIPointerInplace(Object string,
+                @Cached StringToNativeNode stringToNativeNode) {
+            var pointer = stringToNativeNode.executeToNative(this, string, true);
+
+            final RubyPointer instance = new RubyPointer(
+                    coreLibrary().truffleFFIPointerClass,
+                    getLanguage().truffleFFIPointerShape,
+                    pointer);
+            AllocationTracing.trace(instance, this);
+            return instance;
         }
     }
 
-    @CoreMethod(names = "string_to_ffi_pointer", onSingleton = true, required = 1)
-    public abstract static class StringToFFIPointerNode extends CoreMethodArrayArgumentsNode {
+    @CoreMethod(names = "string_to_ffi_pointer_copy", onSingleton = true, required = 1)
+    public abstract static class StringToFFIPointerCopyNode extends CoreMethodArrayArgumentsNode {
 
         @Specialization
-        RubyPointer toNative(Object string,
+        RubyPointer toFFIPointerCopy(Object string,
                 @Cached StringToNativeNode stringToNativeNode) {
-            var pointer = stringToNativeNode.executeToNative(this, string);
+            var pointer = stringToNativeNode.executeToNative(this, string, false);
 
             final RubyPointer instance = new RubyPointer(
                     coreLibrary().truffleFFIPointerClass,

src/main/java/org/truffleruby/core/format/convert/StringToPointerNode.java

@@ -42,7 +42,7 @@ static long toPointer(VirtualFrame frame, Object string,
             @Cached RubyStringLibrary strings,
             @Bind("this") Node node) {
 
-        final Pointer pointer = stringToNativeNode.executeToNative(node, string);
+        final Pointer pointer = stringToNativeNode.executeToNative(node, string, true);
 
         List<Pointer> associated = (List<Pointer>) frame.getObject(FormatFrameDescriptor.ASSOCIATED_SLOT);
 

src/main/java/org/truffleruby/core/string/ImmutableRubyString.java

@@ -80,21 +80,20 @@ public boolean isNative() {
     }
 
     @SuppressFBWarnings("IS2_INCONSISTENT_SYNC")
-    public Pointer getNativeString(RubyLanguage language) {
+    public Pointer getNativeString(RubyLanguage language, RubyContext context) {
         if (nativeString == null) {
-            return createNativeString(language);
+            return createNativeString(language, context);
         }
         return nativeString;
     }
 
     @TruffleBoundary
-    private synchronized Pointer createNativeString(RubyLanguage language) {
+    private synchronized Pointer createNativeString(RubyLanguage language, RubyContext context) {
         if (nativeString == null) {
             var tencoding = getEncodingUncached().tencoding;
             int byteLength = tstring.byteLength(tencoding);
-            nativeString = CExtNodes.StringToNativeNode.allocateAndCopyToNative(language,
-                    RubyLanguage.getCurrentContext(), tstring, tencoding, byteLength,
-                    TruffleString.CopyToNativeMemoryNode.getUncached());
+            nativeString = CExtNodes.StringToNativeNode.allocateAndCopyToNative(language, context, tstring, tencoding,
+                    byteLength, TruffleString.CopyToNativeMemoryNode.getUncached());
         }
         return nativeString;
     }