armv7-unknown-linux-gnueabihf target spec contains apparently nonsensical feature combination

[RalfJung]

The target spec for this target sets the following features: +v7,+vfp3,-d32,+thumb2,-neon. However, we have also set vfp3 to imply d32, which means -d32 implies -vfp3, so this makes little sense -- either the +vfp3 or the -d32 must be wrong. Or did I misunderstand something?

We don't have target maintainers listed for that target so I am not sure whom to ping... Cc @workingjubilee @beetrees

[RalfJung]

@rustbot ping arm

[rustbot]

Hey ARM Group! This bug has been identified as a good "ARM candidate".
In case it's useful, here are some instructions for tackling these sorts of
bugs. Maybe take a look?
Thanks! <3

cc @adamgemmell @davidtwco @hug-dev @jacobbramley @JamieCunliffe @joaopaulocarreiro @raw-bin @Stammark

[workingjubilee]

Huh.

I believe it's trying to indicate specifically the "vfp3-d16" configuration.

[workingjubilee]

vfp3 implying d32 doesn't actually make sense, I believe.

[RalfJung]

vfp3 implying d32 doesn't actually make sense, I believe.

That was apparently added all the way back in #128221. Cc @calebzulawski @Amanieu

[calebzulawski]

The table was adapted from LLVM, though I could have made a mistake. This is the current relationship between vfp version and d32 (I'm having a little trouble parsing it): https://github.com/llvm/llvm-project/blob/8f36135aea5dfbb5f090ca9ad055094c9913f735/llvm/lib/Target/ARM/ARMFeatures.td#L73

[RalfJung]

I don't see that line being about vfp3? vfp3 is defined a few lines down, here. It seems to imply vfp2 but nothing else.

[adamgemmell]

I don't see that line being about vfp3? vfp3 is defined a few lines down, here. It seems to imply vfp2 but nothing else.

That's my impression too, d32 looks to be independent from any others. To me the multiclass directive is defining combinatorial features like vfpXsp, similar to the vfp3-d16 one jubillee mentioned above

Interestingly, vfp2 used to imply d32 for a little while, though this was due to a bug from about 6 years ago so might be unrelated

[RalfJung]

I can't parse this multiclass thing at all.^^