https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83156
--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> --- Author: segher Date: Wed Nov 29 22:42:37 2017 New Revision: 255260 URL: https://gcc.gnu.org/viewcvs?rev=255260&root=gcc&view=rev Log: combine: Do not throw away unneeded arms of parallels (PR83156) The fix for PR82621 makes us not split an I2 if one of the results of those SETs is unused, since combine does not handle that properly. But this results in degradation for i386 (or more in general, for any target that does not have patterns for parallels with an unused result as a CLOBBER instead of a SET for that result). This patch instead makes us not split only if one of the results is set again before I3. That fixes PR83156 and also fixes PR82621. Unfortunately it undoes the nice optimisations that the previous patch did on powerpc. PR rtl-optimization/83156 PR rtl-optimization/82621 * combine.c (try_combine): Don't split an I2 if one of the dests is set again before I3. Allow unused dests. Modified: trunk/gcc/ChangeLog trunk/gcc/combine.c
