https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70674
--- Comment #2 from Andreas Krebbel <krebbel at gcc dot gnu.org> --- Author: krebbel Date: Wed Apr 20 07:09:32 2016 New Revision: 235233 URL: https://gcc.gnu.org/viewcvs?rev=235233&root=gcc&view=rev Log: PR70674: S/390: Add memory barrier to stack pointer restore from fpr. This patches fixes a problem with stack variable accesses being scheduled after the stack pointer restore instructions. In the testcase this happened with the stack variable 'a' accessed through the frame pointer. The existing stack_tie we have in the backend is basically useless when trying to block stack variable accesses from being scheduled across an insn. The alias set of stack variables and the frame alias set usually differ and hence aren't in conflict with each other. The solution appears to be a magic MEM term with a scratch register which is handled as a full memory barrier when analyzing scheduling dependencies. With the patch a (clobber (mem:BLK (scratch))) is being added to the restore instruction in order to prevent any memory operations to be scheduled across the insn. The patch does that only for the one case where the stack pointer is restored from an FPR. Theoretically this might happen also in the case where the stack pointer gets restored using a load multiple. However, triggering that problem with load-multiple appears to be much harder since the load-multiple will restore the frame pointer as well. So in order to see the problem a different call-clobbered register would need to be used as temporary stack pointer. Another case which needs to be handled some day is the stack pointer allocation part. It needs to be a memory barrier as well. Bootstrapped and regression tested with --with-arch z196 and z13 on s390 and s390x. gcc/ChangeLog: 2016-04-20 Andreas Krebbel <kreb...@linux.vnet.ibm.com> Backport from mainline 2016-04-20 Andreas Krebbel <kreb...@linux.vnet.ibm.com> PR target/70674 * config/s390/s390.c (s390_restore_gprs_from_fprs): Pick the new stack_restore_from_fpr pattern when restoring r15. (s390_optimize_prologue): Strip away the memory barrier in the parallel when trying to get rid of restore insns. * config/s390/s390.md ("stack_restore_from_fpr"): New insn definition for loading the stack pointer from an FPR. Compared to the normal move insn this pattern includes a full memory barrier. gcc/testsuite/ChangeLog: 2016-04-20 Andreas Krebbel <kreb...@linux.vnet.ibm.com> Backport from mainline 2016-04-20 Andreas Krebbel <kreb...@linux.vnet.ibm.com> PR target/70674 * gcc.target/s390/pr70674.c: New test. Added: branches/gcc-5-branch/gcc/testsuite/gcc.target/s390/pr70674.c Modified: branches/gcc-5-branch/gcc/ChangeLog branches/gcc-5-branch/gcc/config/s390/s390.c branches/gcc-5-branch/gcc/config/s390/s390.md branches/gcc-5-branch/gcc/testsuite/ChangeLog
