Always use the fast Time formatter when the format allows it

* So it is much easier to assert the correctness of it.

Author: eregon

src/main/java/org/truffleruby/core/time/RubyDateFormatter.java

@@ -566,6 +566,7 @@ public static RopeBuilder formatToRopeBuilder(Token[] compiledPattern, ZonedDate
         return toAppendTo;
     }
 
+    @TruffleBoundary
     public static boolean formatToRopeBuilderCanBeFast(Token[] compiledPattern) {
         for (int i = 0, compiledPatternLength = compiledPattern.length; i < compiledPatternLength; i++) {
             Token token = compiledPattern[i];

src/main/java/org/truffleruby/core/time/TimeNodes.java

@@ -14,7 +14,6 @@
 import com.oracle.truffle.api.dsl.Cached;
 import com.oracle.truffle.api.dsl.ImportStatic;
 import com.oracle.truffle.api.dsl.Specialization;
-import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.library.CachedLibrary;
 import com.oracle.truffle.api.object.Shape;
 import com.oracle.truffle.api.profiles.ConditionProfile;
@@ -417,7 +416,7 @@ public abstract static class TimeStrftimePrimitiveNode extends PrimitiveArrayArg
         @Specialization(
                 guards = { "equalNode.execute(libFormat.getRope(format), cachedFormat)" },
                 limit = "getLanguage().options.TIME_FORMAT_CACHE")
-        protected RubyString timeStrftime(VirtualFrame frame, RubyTime time, Object format,
+        protected RubyString timeStrftime(RubyTime time, Object format,
                 @CachedLibrary(limit = "2") RubyStringLibrary libFormat,
                 @Cached("libFormat.getRope(format)") Rope cachedFormat,
                 @Cached(value = "compilePattern(cachedFormat)", dimensions = 1) Token[] pattern,
@@ -437,6 +436,24 @@ protected RubyString timeStrftime(VirtualFrame frame, RubyTime time, Object form
             }
         }
 
+        @TruffleBoundary
+        @Specialization(guards = "libFormat.isRubyString(format)")
+        protected RubyString timeStrftime(RubyTime time, Object format,
+                @CachedLibrary(limit = "2") RubyStringLibrary libFormat,
+                @Cached RopeNodes.ConcatNode concatNode,
+                @Cached RopeNodes.SubstringNode substringNode) {
+            final Token[] pattern = compilePattern(libFormat.getRope(format));
+            if (formatToRopeBuilderCanBeFast(pattern) && yearIsFast(time)) {
+                return makeStringNode.fromRope(RubyDateFormatter.formatToRopeBuilderFast(
+                        pattern,
+                        time.dateTime,
+                        concatNode,
+                        substringNode));
+            } else {
+                return makeStringNode.fromBuilderUnsafe(formatTime(time, pattern), CodeRange.CR_UNKNOWN);
+            }
+        }
+
         protected boolean formatToRopeBuilderCanBeFast(Token[] pattern) {
             return RubyDateFormatter.formatToRopeBuilderCanBeFast(pattern);
         }
@@ -447,15 +464,6 @@ protected boolean yearIsFast(RubyTime time) {
             return year >= 1000 && year <= 9999;
         }
 
-        @Specialization(guards = "libFormat.isRubyString(format)")
-        protected RubyString timeStrftime(VirtualFrame frame, RubyTime time, Object format,
-                @CachedLibrary(limit = "2") RubyStringLibrary libFormat) {
-            final Token[] pattern = compilePattern(libFormat.getRope(format));
-            return makeStringNode.fromBuilderUnsafe(
-                    formatTime(time, pattern),
-                    CodeRange.CR_UNKNOWN);
-        }
-
         protected Token[] compilePattern(Rope format) {
             return RubyDateFormatter.compilePattern(format, false, getContext(), this);
         }