http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37273
--- Comment #5 from Jeffrey A. Law <law at redhat dot com> 2011-01-12 13:38:20 UTC --- First I think we need to note that if we allocate the pseudo holding the value for "ext" in memory that we get some savings (because "ext" is already sitting in memory waiting to be used). This is very similar to how we recognize some savings from allocating a pseudo to memory when the pseudo represents an argument loaded from its stack slot in ira-costs. Second, in that same code, we're double-counting the cost of allocating the pseudo to memory. If those two problems are fixed, we get the desired PPC code; however, significant benchmarking would be required to determine how this change affects a broader codebase. I'll note there's also a deficiency in caller-saves in that it insists on reloading the value into its original hard reg, even if the hard reg is going to be immediately copied to a different hard reg. I don't want to spend too much time on the caller-save aspects since ultimately I think caller-save needs to go away or at least have another rewrite. It's approaching 2 decades since it's last major revision.
