https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63501
--- Comment #3 from Michael Meissner <meissner at gcc dot gnu.org> --- The -mupper-regs-df and -mupper-regs-sf options are a work in progress. I am working on these options right now on a private branch, but the code is not yet ready for incorporation into the tree. I don't know how long it will take to track down the various bugs before the patches are submitted. As I write this, the code in my branch requires the use of the -mlra option (to switch to the LRA register allocator), and -mlra has some issues of its own that we are investigating. I have two spec tests (456.hmmer and 416.gamess) that fail when the -mupper-regs-df -mlra options are used. Of the tests that run, 454.calculix and 470.lbm show about a 6-7% improvement, while 410.bwaves has a 6-7% regression.