[Bug rtl-optimization/82621] [6/7 Regression] wrong code with -Og -fgcse -fweb
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82621 --- Comment #11 from Segher Boessenkool --- Author: segher Date: Wed Nov 29 22:42:37 2017 New Revision: 255260 URL: https://gcc.gnu.org/viewcvs?rev=255260=gcc=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
[Bug rtl-optimization/82621] [6/7 Regression] wrong code with -Og -fgcse -fweb
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82621 Segher Boessenkool changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED --- Comment #10 from Segher Boessenkool --- Fixed on all open branches.
[Bug rtl-optimization/82621] [6/7 Regression] wrong code with -Og -fgcse -fweb
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82621 --- Comment #9 from Segher Boessenkool --- Author: segher Date: Fri Nov 24 17:03:04 2017 New Revision: 255143 URL: https://gcc.gnu.org/viewcvs?rev=255143=gcc=rev Log: combine: Don't split insns if half is unused (PR82621) If we have a PARALLEL of two SETs, and one half is unused, we currently happily split that into two instructions (albeit the unused one is useless). Worse, as PR82621 shows, combine will happily merge this insn into I3 even if some intervening insn sets the same register again, which is wrong. This fixes it by not splitting PARALLELs with REG_UNUSED notes. It all is handled fine by combine in that case; just the "single set that is unused" case isn't handled properly. This also results in better code: combine will now actually throw away the unused SET. (It still won't do that in an I3). PR rtl-optimization/82621 * combine.c (try_combine): Do not split PARALLELs of two SETs if the dest of one of those SETs is unused. Modified: branches/gcc-6-branch/gcc/ChangeLog branches/gcc-6-branch/gcc/combine.c
[Bug rtl-optimization/82621] [6/7 Regression] wrong code with -Og -fgcse -fweb
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82621 --- Comment #8 from Segher Boessenkool --- Author: segher Date: Fri Nov 24 17:00:57 2017 New Revision: 255142 URL: https://gcc.gnu.org/viewcvs?rev=255142=gcc=rev Log: combine: Don't split insns if half is unused (PR82621) If we have a PARALLEL of two SETs, and one half is unused, we currently happily split that into two instructions (albeit the unused one is useless). Worse, as PR82621 shows, combine will happily merge this insn into I3 even if some intervening insn sets the same register again, which is wrong. This fixes it by not splitting PARALLELs with REG_UNUSED notes. It all is handled fine by combine in that case; just the "single set that is unused" case isn't handled properly. This also results in better code: combine will now actually throw away the unused SET. (It still won't do that in an I3). PR rtl-optimization/82621 * combine.c (try_combine): Do not split PARALLELs of two SETs if the dest of one of those SETs is unused. Modified: branches/gcc-7-branch/gcc/ChangeLog branches/gcc-7-branch/gcc/combine.c
[Bug rtl-optimization/82621] [6/7 Regression] wrong code with -Og -fgcse -fweb
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82621 --- Comment #7 from Segher Boessenkool --- *** Bug 81291 has been marked as a duplicate of this bug. ***
