hexagon: Add scalar DSP intrinsics

[androm3da]

Add scalar (non-HVX) intrinsic wrappers for Hexagon DSP operations covering arithmetic, multiply, shift, saturate, compare, and floating-point instructions, mapping to llvm.hexagon.* LLVM builtins.

Includes the stdarch-gen-hexagon-scalar code generator crate which produces scalar.rs from the LLVM hexagon_protos.h header file, and a CI step to verify the generated output stays in sync.

[rustbot]

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[androm3da]

cc @quic-mliebel

[quic-mliebel]

Should the scalar intrinsics have cfg_attr like HVX intrinsics have?

For example:

#[cfg_attr(target_arch = "hexagon", target_feature(enable = "hvxv79"))]
#[cfg_attr(test, assert_instr(vfneg_f8))]

The generator could generate those lines.

[androm3da]

Should the scalar intrinsics have cfg_attr like HVX intrinsics have?

For example:

#[cfg_attr(target_arch = "hexagon", target_feature(enable = "hvxv79"))]
#[cfg_attr(test, assert_instr(vfneg_f8))]

The generator could generate those lines.

Some of them do have a dependency, yes. I'll add this.

[quic-mliebel]

Should the scalar intrinsics have cfg_attr like HVX intrinsics have?
For example:

#[cfg_attr(target_arch = "hexagon", target_feature(enable = "hvxv79"))]
#[cfg_attr(test, assert_instr(vfneg_f8))]

The generator could generate those lines.

Some of them do have a dependency, yes. I'll add this.

What about assert_instr?

[androm3da]

Should the scalar intrinsics have cfg_attr like HVX intrinsics have?
For example:

#[cfg_attr(target_arch = "hexagon", target_feature(enable = "hvxv79"))]
#[cfg_attr(test, assert_instr(vfneg_f8))]

The generator could generate those lines.

Some of them do have a dependency, yes. I'll add this.

What about assert_instr?

yeah - we need that. Will fix it.

And we need target features to gate some of these intrinsic too, I'll fix the compiler to provide those.

[androm3da]

we need target features to gate some of these intrinsic too, I'll fix the compiler to provide those.

rust-lang/rust#155014