Inlining Improvements

[Mark Mitchell]

  Martin v. Loewis wrote:
  > > The point is that tree inlining seems to generate better code than RTL
  > > inlining which the C compiler currently does.
  > 
  > Examples?

  Mark Mitchell said so; I believe him.  I haven't used the tree inlining
  compiler yet.

The LANL Pooma II library runs faster with the changes on some of its
benchmarks.  There is *extreme* inlining going on there, and the final
loops are very small.  So, saving one instruction to do one dead store
going away, say, could make a 30% difference.

  There are many fine examples of trivial optimisation not being done with
  inline functions that are done with macros.  I assume most of them will
  occur with tree inlining too (why not?).  But I will have to wait and
  see.

I concur.  I don't expect typical code to see major wins, yet.

One of the things now easy to do (in theory) is scatter-gather of
loads and stores.  That will expose small structures (with two
members, say, like a `complex' class) to the back-end optimizers
(which deal almost exclusively with REGs).

--
Mark Mitchell                   mark@codesourcery.com
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