An introduction and some questions

[Jackson Davis]

Hello,

I've been trying to finally introduce myself to graal over the last few
days, with a hope I can maybe sneak in a few changes when I have time - its
an interesting project :)

On the non-technical side: Whats with the [GR-XXXX] in commit messages, is
this a private issue tracker? I don't see anything on the graal project on
openjdk jira, or anywhere else for that matter.

On the technical side: I've been looking into optimizing the code
generation on x86 for add/sub/shl. Currently, if reg1 and reg2 are
different, reg2 = add reg1, C generates
mov %reg1, %reg2
add C, %reg2

This can be folded into a single lea C(%reg1), %reg2 (if there is no
resulting operation dependent on flags being set). We can do the same for
sub, and for shl if C=1/2/3. I have a very basic attempt of this
working-ish here:
https://github.com/jcdavis/graal/commit/6d27c585726b64259635f36542263ca0cde3dcf1
. This currently always uses leaq, which is at best 1 byte longer than it
needs to be for 32 bit operands (since the REX prefix isn't necessary), and
at worst possibly wrong because over/underflow will set the high order 32
bits (which might be ok? But unsure). It also misses add/sub by 1 (since
those are lowered to MOp, not ConstOp), and also doesn't consider %reg3 =
%reg1 + %reg2 (which can also be represented as an lea)

Where I am a little lost is how to clean this up properly. I was thinking a
new emit function that also takes a source register x could be added, which
be default would still call the same move + emit, and then, individual
opcodes could override that behavior as necessary?

Thanks,
-Jackson