Re: hacking gcc (new optimization)

[Jeff Law <law at redhat dot com>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 04/04/11 12:31, kevin diggs wrote:
> Hi,
> 
> Would it be correct to say that the (target machine influenced) RTL
> representation has ... less intelligence (wrong word?) than the tree
> representation (GENERIC or GIMPLE)? Sort of like describing a circle
> with a point and radius or as a polygon?
They're not directly comparable.  For some things gimple is a better IR,
for other things RTL is a better IR.

> 
> I am trying to figure out where to place this optimization? Early
> where the tree is still available or purely in the RTL (where from
> various reading most other optimizations take place)?
It'll depend on what kind of optimization you're doing.

> 
> Can someone suggest a good optimization (available in the 3.4.6acene
> era) to study?
Similarly.  To be able to suggest an optimization pass to look at for
reference, we need to know more about the optimization you're proposing.

> 
> Finally, does the 3.4.6 tree representation have a name? Was it called
> GENERIC? Or is that 4.x only? Are they similar (4.x is a revision of
> 3.4.6)?
Prior to GCC 4, trees were trees, there was no gimple or generic.  In
fact, it's exceedingly difficult in  compilers prior to GCC 4 to do any
optimizations which require looking at multiple statements at any level
other than RTL.

> The optimization I am working on's goal is to change the way that
> string constants are accessed by architectures like the register
> adequate PowerPC.
More details please.

> 
> I guess another way to ask is, are string literals easily identifiable
> in RTL (I've only started looking at RTL)?
They're easier to identify as trees, as RTL, they may be sitting in the
constant pool, a register if they're only a few chars, etc.

At the tree level, strings will look like strings and they'll be easy to
identify.

jeff

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.11 (GNU/Linux)
Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org/

iQEcBAEBAgAGBQJNmhj9AAoJEBRtltQi2kC7gQAIAIirV/XGcLx8GbdmNi6wYyNr
7jo55wUjZqJfYMjWg/3DQqFHAoa2C2wwvGvJmNeWUNqJrKai0e0oYMSMsSMvAjkO
p0+CKR+AJRiC0CjBEkLCOV9H9i7OeHxInNFAcp9ZgOZNa0ojpIFGWCPuxi8kX4ib
dWGBjJ2MhNgniYgcNczcFyxkpd/2MKuroQoj5Kml9kK9QsaGGJ9FdpDLaxzxRDGQ
J8wzNXiSOx/A1iOieuNzn//oyEuVXlrA0ZKn0BLQpe/ksPBIVPiw98vnaSJCUMGA
oZty8Ro2YP+XL23U5LfJPkCoBz4qwZc1lzoNJxeagtJ/M+iFMtvFDLcbSSJRCgM=
=BKhp
-----END PGP SIGNATURE-----