[Truffle] Add TruffleBoundary to RubyString.toString().

[bpot]

It looks like toString() is triggering some code that truffle refuses to compile.

A script like 1_000_000.times { [1,2,3].inspect } triggers:

Found illegal recursive call to HotSpotMethod<Utility.recursiveAppendNumber(StringBuffer, int, int, int)>, must annotate such calls with @TruffleBoundary!

Not sure if this is the best fix, still trying to wrap my head around truffle/graal. The full backtrace is below.

Context obj com.oracle.graal.nodes.util.GraphUtil$2: Found illegal recursive call to HotSpotMethod<Utility.recursiveAppendNumber(StringBuffer, int, int, int)>, must annotate such calls with @TruffleBoundary!
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Utility.recursiveAppendNumber(StringBuffer, int, int, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Utility.appendNumber(StringBuffer, int, int, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Utility.hex(int, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<UnicodeSet.complement(int, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<UnicodeSet.<init>(int, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<NormalizerImpl.internalGetNXHangul()>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<NormalizerImpl.internalGetNX(int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<NormalizerImpl.getNX(int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<NormalizerBase.decompose(String, boolean, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<NormalizerBase$NFKDMode.normalize(String, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<NormalizerBase.normalize(String, Normalizer$Form, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<NormalizerBase.normalize(String, Normalizer$Form)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Normalizer.normalize(CharSequence, Normalizer$Form)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Pattern.normalize()>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Pattern.compile()>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Pattern.<init>(String, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Pattern.compile(String)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<String.split(String, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<String.split(String)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<ExtendedCharsets.init()>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<AbstractCharsetProvider.charsetForName(String)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Charset.lookupExtendedCharset(String)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Charset.lookup2(String)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Charset.lookup(String)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Charset.defaultCharset()>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<StringCoding.decode(byte[], int, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<String.<init>(byte[], int, int)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<String.<init>(byte[])>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Encoding.toString()>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<EncodingService.charsetForEncoding(Encoding)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<Helpers.decodeByteList(Ruby, ByteList)>
                                                                            Context obj com.oracle.graal.hotspot.meta.HotSpotMetaAccessProvider@19e332a3
                                                                            Context obj HotSpotMethod<RubyString.toString()>

[chrisseaton]

Hi! Thanks very much of this - sorry I didn't respond earlier but for some reason the email didn't catch my eye.

The problem behind this is that Truffle cannot compile unbound recursion. The partial evaluation technique we use is sort of like exhaustive inlining, so recursion is a problem, and for some reason the standard JDK toString methods are often implemented recursively.

You are correct that we probably need @TruffleBoundary here. There is already a RubyNode.notDesignedForCompilation() which should have given you a more sensible error, but for some reason this directive is sometimes missed at the moment.

Thanks again.

[bpot]

Cool! Thanks for the explanation.