On 07/09/2018 10:38 AM, Richard Earnshaw wrote: > This patch is the main part of the speculation tracking code. It adds > a new target-specific pass that is run just before the final branch > reorg pass (so that it can clean up any new edge insertions we make). > The pass is only run with -mtrack-speculation is passed on the command > line. > > One thing that did come to light as part of this was that the stack pointer > register was not being permitted in comparision instructions. We rely on > that for moving the tracking state between SP and the scratch register at > function call boundaries. Note that the sp in comparison instructions issue came up with the improvements to stack-clash that Tamar, Richard S. and you worked on.
> > * config/aarch64/aarch64-speculation.cc: New file. > * config/aarch64/aarch64-passes.def (pass_track_speculation): Add before > pass_reorder_blocks. > * config/aarch64/aarch64-protos.h (make_pass_track_speculation): Add > prototype. > * config/aarch64/aarch64.c (aarch64_conditional_register_usage): Fix > X14 and X15 when tracking speculation. > * config/aarch64/aarch64.md (register name constants): Add > SPECULATION_TRACKER_REGNUM and SPECULATION_SCRATCH_REGNUM. > (unspec): Add UNSPEC_SPECULATION_TRACKER. > (speculation_barrier): New insn attribute. > (cmp<mode>): Allow SP in comparisons. > (speculation_tracker): New insn. > (speculation_barrier): Add speculation_barrier attribute. > * config/aarch64/t-aarch64: Add make rule for aarch64-speculation.o. > * config.gcc (aarch64*-*-*): Add aarch64-speculation.o to extra_objs. > * doc/invoke.texi (AArch64 Options): Document -mtrack-speculation. > --- > gcc/config.gcc | 2 +- > gcc/config/aarch64/aarch64-passes.def | 1 + > gcc/config/aarch64/aarch64-protos.h | 3 +- > gcc/config/aarch64/aarch64-speculation.cc | 494 > ++++++++++++++++++++++++++++++ > gcc/config/aarch64/aarch64.c | 13 + > gcc/config/aarch64/aarch64.md | 30 +- > gcc/config/aarch64/t-aarch64 | 10 + > gcc/doc/invoke.texi | 10 +- > 8 files changed, 558 insertions(+), 5 deletions(-) > create mode 100644 gcc/config/aarch64/aarch64-speculation.cc Given the consensus forming about using these kind of masking instructions being the preferred way to mitigate (as opposed to lfence barriers and the like) I have to ask your opinions about making the bulk of this a general pass rather than one specific to the aarch backend. I'd hate to end up duplicating all this stuff across multiple architectures. I think it all looks pretty reasonable though. jeff
