On Fri, Mar 18, 2011 at 12:23:11PM -0400, Kenneth Zadeck wrote: > I believe that this is not the right way to go. > > if someone specifies -fcrossjumping, then the pass should turn on > live for the duration of the pass just as ifcvt does. If they ask > for crossjumping you should give them crossjumping and not some > crippled version of it.
Such (untested) patch is in http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48156#c7 But Paolo just added comment there that he prefers this version. Is the live problem so much more useful for crossjumping than lr problem? All it wants to prove is if it can safely move a couple of instructions across some other instructions, and the live_union bitmap that is computed using the live/lr problem is used to find out if registers set by the moved instructions are actually live at the end of those instructions or not. What would be an example where live problem would allow optimizing more than lr? Jakub
