Hi Andrew: It's safe to execute on old machine, but it is still a new extension not included on baseline ISA, so I still prefer having -march to guard that, and then we can track that in the ELF attribute to see what extensions and which version are used in the executable / object files.
On Thu, Jan 7, 2021 at 11:51 AM Andrew Waterman <aswater...@gmail.com> wrote: > I've got a contrary opinion: > > Since HINTs are guaranteed to execute as no-ops--e.g., this one is > just a FENCE instruction, which is already a mandatory part of the > base ISA--they don't _need_ to be called out as separate extensions in > the toolchain. > > Although there's nothing fundamentally wrong with Kito's suggestion, > it seems like an extra hoop to jump through without commensurate > benefit. I see no reason to restrict the use of __builtin_pause, > since all RISC-V implementations, including old ones, are required to > support it. And, of course, that's the reason we encoded it this way > :) > > > On Wed, Jan 6, 2021 at 7:35 PM Kito Cheng <kito.ch...@gmail.com> wrote: > > > > Hi Philipp: > > > > Could you add zihintpause to -march parser and guard that on the > > pattern and builtin like zifencei[1-2]? > > > > And could you sent a PR to > > https://github.com/riscv/riscv-c-api-doc/blob/master/riscv-c-api.md to > > mention __builtin_riscv_pause? > > > > Thanks! > > > > [1] march parser change: > > > https://github.com/gcc-mirror/gcc/commit/b03be74bad08c382da47e048007a78fa3fb4ef49 > > [2] Default version for ext.: > > > https://github.com/gcc-mirror/gcc/commit/4b81528241ca682025d92558ff6aeec91dafdca8 > > > > > > > --- /dev/null > > > +++ b/gcc/testsuite/gcc.target/riscv/builtin_pause.c > > > @@ -0,0 +1,10 @@ > > > +/* { dg-do compile } */ > > > +/* { dg-options "-O2" } */ > > > + > > > +void test_pause() > > > > I would suggest you change the function name in the testcase, > > otherwise the scan-assembler test will always pass even if you didn't > > generate "pause" instruction. > > > > > > > +{ > > > + __builtin_riscv_pause (); > > > +} > > > + > > > +/* { dg-final { scan-assembler "pause" } } */ > > > + > > > -- > > > 2.18.4 > > > >
