On Tue, Jan 30, 2024 at 11:40 AM Richard Sandiford <richard.sandif...@arm.com> wrote: > > Richard Biener <richard.guent...@gmail.com> writes: > > On Mon, Jan 29, 2024 at 5:00 PM Richard Sandiford > > <richard.sandif...@arm.com> wrote: > >> > >> Tamar Christina <tamar.christ...@arm.com> writes: > >> > Hi All, > >> > > >> > Recently something in the midend had started inverting the branches by > >> > inverting > >> > the condition and the branches. > >> > > >> > While this is fine, it makes it hard to actually test. In RTL I disable > >> > scheduling and BB reordering to prevent this. But in GIMPLE there seems > >> > to be > >> > nothing I can do. __builtin_expect seems to have no impact on the > >> > change since > >> > I suspect this is happening during expand where conditions can be flipped > >> > regardless of probability during compare_and_branch. > >> > > >> > Since the mid-end has plenty of correctness tests, this weakens the > >> > backend > >> > tests to just check that a correct looking sequence is emitted. > >> > > >> > Bootstrapped Regtested on aarch64-none-linux-gnu and no issues. > >> > > >> > Ok for master? > >> > > >> > Thanks, > >> > Tamar > >> > > >> > gcc/testsuite/ChangeLog: > >> > > >> > PR testsuite/113502 > >> > * gcc.target/aarch64/sve/vect-early-break-cbranch.c: Ignore exact > >> > branch. > >> > * gcc.target/aarch64/vect-early-break-cbranch.c: Likewise. > >> > >> OK I guess, since I agree that the "polarity" of the branch isn't really > >> the > >> thing that we're trying to test. But the fact that even __builtin_expect > >> doesn't work seems like a bug. Do we have a PR for that? Might be worth > >> filing one (for GCC 15+) if we don't. > > > > But that only should affect which edge is fallthru, not the "polarity" > > of the branch, no? > > Right, that's what I meant by "polarity". I should have used a proper > term, sorry. The conditions in the patch are inverses of each other, > but it seems like the choice between them should be predictable if > the branch is very likely or very unlikely.
I'm not sure, esp. if you disable BB reordering which might be the one flipping the polarity to keep fallthru/backedge in-order. Richard. > Thanks, > Richard >
