[llvm-dev] [RFC] Upstream development of support for yet-to-be-ratified RISC-V extensions

James Y Knight via llvm-dev llvm-dev at lists.llvm.org
Wed Jan 22 13:20:43 PST 2020

Yeah. I didn't mean to actually suggest that the compiler emit a warning
diagnostic when you pass the flag. I only meant that an appropriately named
flag would be, itself, a warning sign against inappropriate use, simply by
its name, and the user having to explicitly pass it.

On Wed, Jan 22, 2020 at 2:55 PM Chris Lattner via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Jan 21, 2020, at 5:00 AM, Alex Bradbury <asb at lowrisc.org> wrote:
> >> This all makes sense to me.
> >
> > That's correct, thanks for the feedback.
> >
> > I do like the idea from James of having the compiler always spit out a
> > note when enabling the experimental extension, warning of its
> > experimental nature. If we had such a warning and additionally
> > required a `-riscv-enable-experimental-extensions` or similar, then I
> > think there could be merit in including in the ISA string as Simon
> > suggests, especially as we're likely to start putting that string in
> > ELF output etc.
> Are you suggesting this behavior from Clang or from LLVM?  I think it
> would be a bad thing for LLVM to produce this warning: there isn’t a
> precedent for this, and it breaks the library-based design goals.  Having
> clang produce a warning could be done, but it would be very noisy (one
> warning for every .c file in a build) and I’m not sure how much value it
> provides.
> -Chris
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