Debug option fun
I just extended the -XX:+SharkTraceInstalls debug option to print out a load more stuff, statistics on the code size and the number of non-volatile registers used and so on. If you run with it you’ll get something like this:
[0xd04bd010-0xd04bd1b4): java.lang.String::hashCode (420 bytes code, 32 bytes stack, 1 register) [0xd04bd1c0-0xd04bd81c): java.lang.String::lastIndexOf (1628 bytes code, 80 bytes stack, 13 registers) [0xd04bd820-0xd04bdc3c): java.lang.String::equals (1052 bytes code, 48 bytes stack, 5 registers) [0xd04bdc40-0xd04be2f8): java.lang.String::indexOf (1720 bytes code, 80 bytes stack, 12 registers) [0xd04be300-0xd04beaf4): java.io.UnixFileSystem::normalize (2036 bytes code, 80 bytes stack, 12 registers) [0xd04beb00-0xd04c3310): sun.nio.cs.UTF_8$Encoder::encodeArrayLoop (18448 bytes code, 96 bytes stack, 15 registers) [0xd04c3320-0xd04c348c): java.lang.String::charAt (364 bytes code, 32 bytes stack, 1 register) [0xd04c3490-0xd04c3530): java.lang.Object::(160 bytes code, 16 bytes stack, 0 registers) …
This isn’t (just) because I like debug options. Lately I’ve thought of a couple of optimizations I could do, one to reduce the code size for methods with more than one return, and one to cut the number of registers used. The former probably won’t do a lot other than reducing compile time, but the latter should be well worth it. Maybe not so much on PowerPC — though I already have a couple of methods maxed out on registers — but not all platforms have the luxury of 19 caller-save registers! And, of course, if I’m going to spend time optimizing then I want to see it worked…
Whilst we’re on the subject of options I found another funky one: -XX:+VerifyBeforeGC. I’ve already fixed one bug using it!