Fix target-cpu fpu features on Armv8-R.

[chrisnc]

This is a follow-up to #123159, but applied to Armv8-R.

This required llvm/llvm-project#88287 to work properly. Now that this change exists in rustc's llvm, we can fix Armv8-R's default fpu features. In Armv8-R's case, the default features from LLVM for floating-point are sufficient, because there is no integer-only variant of this architecture.

[rustbot]

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

[jieyouxu]

cc @workingjubilee since you looked at #123159, I'll reroll this PR to you too.

r? @workingjubilee

[jieyouxu]

And since it might help bisection in the future,
@bors rollup=never

[chrisnc]

Confirmed that with this change, -C target-cpu=cortex-r52 now allows double-precision and neon instructions to be generated, according to the additional features implied by this CPU in LLVM.

#![no_main]
#![no_std]

#[no_mangle]
pub fn foo(x: f64, y: f64) -> f64 {
    x + y
}

#[no_mangle]
pub fn bar(x: &mut [f32; 4], y: &[f32; 4]) {
    for i in 0..4 {
        x[i] += y[i];
    }
}

use core::panic::PanicInfo;

#[panic_handler]
fn panic(_panic: &PanicInfo<'_>) -> ! {
    loop {}
}

$ build/aarch64-apple-darwin/stage1/bin/rustc --emit=obj --target armv8r-none-eabihf foo.rs -C target-cpu=cortex-r52 -C opt-level=3

polus:rust$ objdump -d foo.o

foo.o:  file format elf32-littlearm

Disassembly of section .text.foo:

00000000 <foo>:
       0: ee300b01      vadd.f64        d0, d0, d1
       4: e12fff1e      bx      lr

Disassembly of section .text.bar:

00000000 <bar>:
       0: f4610a8f      vld1.32 {d16, d17}, [r1]
       4: f4602a8f      vld1.32 {d18, d19}, [r0]
       8: f2400de2      vadd.f32        q8, q8, q9
       c: f4400a8f      vst1.32 {d16, d17}, [r0]
      10: e12fff1e      bx      lr

Disassembly of section .text.rust_begin_unwind:

00000000 <rust_begin_unwind>:
       0: eafffffe      b       0x0 <rust_begin_unwind> @ imm = #-8

Output on the immediate ancestor commit:

$ build/aarch64-apple-darwin/stage1/bin/rustc --emit=obj --target armv8r-none-eabihf foo.rs -C target-cpu=cortex-r52 -C opt-level=3

$ objdump -d foo.o

foo.o:  file format elf32-littlearm

Disassembly of section .text.foo:

00000000 <foo>:
       0: e92d4800      push    {r11, lr}
       4: ec510b10      vmov    r0, r1, d0
       8: ec532b11      vmov    r2, r3, d1
       c: ebfffffe      bl      0xc <foo+0xc>           @ imm = #-8
      10: ec410b10      vmov    d0, r0, r1
      14: e8bd8800      pop     {r11, pc}

Disassembly of section .text.bar:

00000000 <bar>:
       0: ed910a00      vldr    s0, [r1]
       4: ed911a01      vldr    s2, [r1, #4]
       8: ed912a02      vldr    s4, [r1, #8]
       c: ed913a03      vldr    s6, [r1, #12]
      10: ed904a00      vldr    s8, [r0]
      14: ed905a01      vldr    s10, [r0, #4]
      18: ed906a02      vldr    s12, [r0, #8]
      1c: ed907a03      vldr    s14, [r0, #12]
      20: ee300a04      vadd.f32        s0, s0, s8
      24: ee311a05      vadd.f32        s2, s2, s10
      28: ee322a06      vadd.f32        s4, s4, s12
      2c: ee333a07      vadd.f32        s6, s6, s14
      30: ed800a00      vstr    s0, [r0]
      34: ed801a01      vstr    s2, [r0, #4]
      38: ed802a02      vstr    s4, [r0, #8]
      3c: ed803a03      vstr    s6, [r0, #12]
      40: e12fff1e      bx      lr

Disassembly of section .text.rust_begin_unwind:

00000000 <rust_begin_unwind>:
       0: eafffffe      b       0x0 <rust_begin_unwind> @ imm = #-8

[workingjubilee]

@chrisnc My apologies, for your good deeds will not go unpunished, as now I have to ask:

Can you add that as a test?

[chrisnc]

Punishment accepted. Could you point me to an example that would be good to follow? The tests I see in tests/assembly seem to not have any operators, and adding the code like above in one of those tests requires turning on a bunch of lang items and I can't seem to get it to work...

Here's roughly where I got, but it doesn't compile because no_core disables everything, and if I try to use core, it won't be available in the test. I assume I'm doing this wrong.

// Test that Neon instructions are emitted when a target-cpu supporting them is specified.

//@ assembly-output: emit-asm
//@ compile-flags: --target armv8r-none-eabihf
//@ compile-flags: -C target-cpu=cortex-r52
//@ compile-flags: -C opt-level=3
//@ needs-llvm-components: arm

#![feature(no_core, lang_items)]
#![no_std]
#![no_core]
#![crate_type = "lib"]

#[lang = "sized"]
trait Sized {}

#[lang = "copy"]
trait Copy {}

// CHECK-LABEL: vadd_q:
#[no_mangle]
pub fn vadd_q(x: &mut [f32; 4], y: &[f32; 4]) {
    // CHECK: vld{{.*}}
    // CHECK: vld{{.*}}
    // CHECK: vadd.f32 {{.*}}
    // CHECK: vst{{.*}}
    // CHECK: bx lr
    let mut i = 0usize;
    while i < 4usize {
        x[i] += y[i];
        i += 1usize;
    }
}

// CHECK-LABEL: vadd_f64:
#[no_mangle]
pub fn vadd_f64(x: f64, y: f64) -> f64 {
    // CHECK: vadd.f64 d0, d0, d1
    // CHECK: bx lr
    x + y
}

output:

error[E0369]: binary operation `<` cannot be applied to type `usize`
  --> /Users/chrisnc/src/rust/tests/assembly/armv8r-target-cpu.rs:29:13
   |
29 |     while i < 4usize {
   |           - ^ ------ usize
   |           |
   |           usize

error[E0608]: cannot index into a value of type `&mut [f32; 4]`
  --> /Users/chrisnc/src/rust/tests/assembly/armv8r-target-cpu.rs:30:10
   |
30 |         x[i] += y[i];
   |          ^^^

error[E0608]: cannot index into a value of type `&[f32; 4]`
  --> /Users/chrisnc/src/rust/tests/assembly/armv8r-target-cpu.rs:30:18
   |
30 |         x[i] += y[i];
   |                  ^^^

error[E0368]: binary assignment operation `+=` cannot be applied to type `usize`
  --> /Users/chrisnc/src/rust/tests/assembly/armv8r-target-cpu.rs:31:9
   |
31 |         i += 1usize;
   |         -^^^^^^^^^^
   |         |
   |         cannot use `+=` on type `usize`

error[E0369]: cannot add `f64` to `f64`
  --> /Users/chrisnc/src/rust/tests/assembly/armv8r-target-cpu.rs:40:7
   |
40 |     x + y
   |     - ^ - f64
   |     |
   |     f64

error: aborting due to 5 previous errors

[workingjubilee]

The problem is that this situation is cross-compiling, but I don't believe we actually have a satisfactory way to run cross-compiling of assembly tests beyond the no_core case which is impractical for this example, so I think the actually most satisfactory way is unfortunately probably rmake and filecheck.

[rustbot]

This PR modifies tests/run-make/. If this PR is trying to port a Makefile
run-make test to use rmake.rs, please update the
run-make port tracking issue
so we can track our progress. You can either modify the tracking issue
directly, or you can comment on the tracking issue and link this PR.

cc @jieyouxu

[chrisnc]

Okay, the rmake test is working locally now at least. I'm not sure how to have the same test run for multiple targets, but I've set it up so it will extend to the other target+cpu combinations easily (tested thumbv8m.main-none-eabihf and cortex-m85 also...).

[workingjubilee]

no need to test every single possible subarchitecture, but yes, this looks nice.

I will see if we can't implement actual cross-compiled assembly testing, but for now, this will do quite well, thank you.

@bors r+ rollup

[bors]

📌 Commit d7b2790 has been approved by workingjubilee

It is now in the queue for this repository.

[chrisnc]

Great! Will this actually run in CI? I had to provide a matching target with:
./x test --target=armv8r-none-eabihf tests/run-make/arm-target-cpu-fp for this to run properly, otherwise it would complain about missing core. Is there somewhere I need to specify the invocation needed for this test?

[chrisnc]

Sorry, needed to amend because I realized two things:
my .checks file had leading "//" which are superfluous.

I re-read my comments on the older PR from a few months ago and was reminded that the plan for Armv8-R is that the feature list should be empty, because Arm defines Armv8-R to always have these floating-point features, and so does LLVM, so we don't need to specify them. I've removed the feature setting and updated the comment and commit message to reflect that.

[workingjubilee]

@bors r-

[bors]

💔 Test failed - checks-actions

[chrisnc]

:(
Is there a way to build core from within the rmake.rs so that this will work...?

And would it be okay to break off the test part to another PR and merge the Armv8-R change as-is?

[workingjubilee]

And would it be okay to break off the test part to another PR and merge the Armv8-R change as-is?

Yeah let's do that.

[workingjubilee]

I guess we'll be stuck just straight-up invoking what amounts to -Zbuild-std=core,compiler-builtins for this.

[chrisnc]

Done. Created #130382 for the test.

[workingjubilee]

coolio.

@bors r+ rollup

[bors]

📌 Commit 1a0ba01 has been approved by workingjubilee

It is now in the queue for this repository.

[jieyouxu]

I guess we'll be stuck just straight-up invoking what amounts to -Zbuild-std=core,compiler-builtins for this.

These ones are really unfortunate, there's a couple of run-make tests that seem to need to use bootstrap cargo to -Zbuild-std, but those are really slow. Oh well.