On Wed, 2011-10-05 at 18:21 +0200, Paolo Bonzini wrote: > On 10/05/2011 06:13 PM, William J. Schmidt wrote: > > One other general question about the pattern-match transformation: Is > > this an appropriate transformation for all targets, or should it be > > somehow gated on available addressing modes on the target processor? > > > > Bootstrapped and regression tested on powerpc64-linux-gnu. Verified no > > performance degradations on that target for SPEC CPU2000 and CPU2006. > > > > I'm looking for eventual approval for trunk after any comments are > > resolved. Thanks! > > How do the costs look like for the two transforms you mention in the > head comment of locally_poor_mem_replacement? > > Paolo >
I don't know off the top of my head -- I'll have to gather that information. The issue is that the profitability is really context-sensitive, so just the isolated costs of insns aren't enough. The forward propagation of the add into (mem (reg REG)) looks like a slam dunk in the absence of other information, but if there are other nearby references using nonzero offsets from REG, this just extends the lifetimes of X and Y without eliminating the need for REG.
