On 10/18/19 3:06 AM, Ilya Leoshkevich wrote: > Bootstrapped and regtested on x86_64-redhat-linux, s390x-redhat-linux > and ppc64le-redhat-linux. The offending patch is in gcc-9_1_0-release > and gcc-9_2_0-release - do I need to backport this fix to gcc-9-branch? > > > r266734 has introduced a new instance of jump threading pass in order to > take advantage of opportunities that combine opens up. It was perceived > back then that it was beneficial to delay it after reload, since that > might produce even more such opportunities. > > Unfortunately jump threading interferes with hot/cold partitioning. In > the code from PR92007, it converts the following > > +-------------------------- 2/HOT ------------------------+ > | | > v v > 3/HOT --> 5/HOT --> 8/HOT --> 11/COLD --> 6/HOT --EH--> 16/HOT > | ^ > | | > +-------------------------------+ > > into the following: > > +---------------------- 2/HOT ------------------+ > | | > v v > 3/HOT --> 8/HOT --> 11/COLD --> 6/COLD --EH--> 16/HOT > > This makes hot bb 6 dominated by cold bb 11, and because of this > fixup_partitions makes bb 6 cold as well, which in turn makes EH edge > 6->16 a crossing one. Not only can't we have crossing EH edges, we are > also not allowed to introduce new crossing edges after reload in > general, since it might require extra registers on some targets. > > Therefore, move the jump threading pass between combine and hot/cold > partitioning. Building SPEC 2006 and SPEC 2017 with the old and the new > code indicates that: > > * When doing jump threading right after reload, 3889 edges are threaded. > * When doing jump threading right after combine, 3918 edges are > threaded. > > This means this change will not introduce performance regressions. > > gcc/ChangeLog: > > 2019-10-17 Ilya Leoshkevich <i...@linux.ibm.com> > > PR rtl-optimization/92007 > * cfgcleanup.c (thread_jump): Add an assertion that we don't > call it after reload if hot/cold partitioning has been done. > (class pass_postreload_jump): Rename to > pass_jump_after_combine. > (make_pass_postreload_jump): Rename to > make_pass_jump_after_combine. > * passes.def(pass_postreload_jump): Move before reload, rename > to pass_jump_after_combine. > * tree-pass.h (make_pass_postreload_jump): Rename to > make_pass_jump_after_combine. > > gcc/testsuite/ChangeLog: > > 2019-10-17 Ilya Leoshkevich <i...@linux.ibm.com> > > PR rtl-optimization/92007 > * g++.dg/opt/pr92007.C: New test (from Arseny Solokha). OK for trunk and gcc-9 branch.
jeff
