Currently, the java.util.Formatter$Conversion::isValid method is implemented based on switch, which cannot be inlined because codeSize > 325. This problem can be avoided by implementing it with ImmutableBitSetPredicate.

use -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlining to see the master branch:

@ 109 java.util.Formatter$Conversion::isValid (358 bytes) failed to inline: hot method too big
current version

@ 109 java.util.Formatter$Conversion::isValid (10 bytes) inline (hot)
  @ 4 jdk.internal.util.ImmutableBitSetPredicate$SmallImmutableBitSetPredicate::test (50 bytes) inline (hot)