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compiler: add simd_ctpop intrinsic #125266

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merged 4 commits into from
May 21, 2024

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workingjubilee
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Fairly straightforward addition.

cc @rust-lang/opsem new (extremely boring) intrinsic

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rustbot commented May 19, 2024

r? @jieyouxu

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels May 19, 2024
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rustbot commented May 19, 2024

Some changes occurred to the platform-builtins intrinsics. Make sure the
LLVM backend as well as portable-simd gets adapted for the changes.

cc @antoyo, @GuillaumeGomez, @bjorn3, @calebzulawski, @programmerjake

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workingjubilee commented May 19, 2024

Some changes occurred to the platform-builtins intrinsics. Make sure the
LLVM backend as well as portable-simd gets adapted for the changes.

Yes, that's the idea.

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r? @RalfJung

looks good to me

@rustbot rustbot assigned RalfJung and unassigned jieyouxu May 19, 2024
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saethlin commented May 19, 2024

I presume it's implausible for this intrinsic to have a fallback body because we can't actually write the generic bound?

Can we then add Miri support? I feel like it shouldn't be too hard, the boilerplate is already reusable in this function:

/// Calls the simd intrinsic `intrinsic`; the `simd_` prefix has already been removed.
/// Returns `Ok(true)` if the intrinsic was handled.
fn emulate_simd_intrinsic(

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I presume it's implausible for this intrinsic to have a fallback body because we can't actually write the generic bound?

Can we then add Miri support? I feel like it shouldn't be too hard, the boilerplate is already reusable in this function:

/// Calls the simd intrinsic `intrinsic`; the `simd_` prefix has already been removed.
/// Returns `Ok(true)` if the intrinsic was handled.
fn emulate_simd_intrinsic(

I can add Miri support yeah.

I'm not sure what adding a fallback body would look like here, it might be possible to twist the code such that it actually works, tbh.

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@saethlin hmm so wait I looked around and didn't see a magic wand to wave... am I supposed to just, for a fallback body, literally write a body for the intrinsic?

lemme think about that, it might work.

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hm. I know how to add the appropriate generic bounds, they just might make someone mad.

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Happy to review a Miri implementation, but LLVM codegen is not something I can confidently review.
r? @nikic

We haven't yet used a fallback body for any SIMD intrinsic so maybe this is not the right time and place for that experiment. :) (It could delay the PR quite a bit, trying to get that to work.)

@rustbot rustbot assigned nikic and unassigned RalfJung May 19, 2024
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bjorn3 commented May 19, 2024

Would you mind adding cg_clif support too at

? Cranelift calls the instruction that needs to be used here popcnt:
let res = fx.bcx.ins().popcnt(val);

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hm. I know how to add the appropriate generic bounds, they just might make someone mad.

They will leak into the std::simd interface, which we don't want

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workingjubilee commented May 19, 2024

hm. I know how to add the appropriate generic bounds, they just might make someone mad.

They will leak into the std::simd interface, which we don't want

Ehn, we already have the relevant bounds or approximately so.

As Ralf said, it would delay things significantly, that's the real reason.

Yeah, I noticed that cg_clif and cg_gcc were already parsing the LLVM intrinsic, which made me surprised no one added this yet. 👀

I'll add the followups.

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Miri support should be pretty easy -- just another case here that maps to Op::Numeric(sym::ctpop). This completes the support for the "numeric" intrinsics, except for the nonzero variants.

For tests I think this function would be good.

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rustbot commented May 20, 2024

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

The Miri subtree was changed

cc @rust-lang/miri

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workingjubilee commented May 20, 2024

I briefly glanced at cg_gcc but I do not understand the relevant code for the popcount implementation, which appears to have many edge-cases, and does not seem to dispatch to the fast vpopcount builtins anyways, only doing that for pattern-matching LLVMIR intrinsics. I hope it won't be too hard to add, but my apologies.

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Neat, thanks for the Miri implementation.

@RalfJung
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r=me on the Miri implementation and test, thanks. :)

let fn_ty = bx.type_func(&[vec_ty, bx.type_i1()], vec_ty);
let dont_poison_on_zero = bx.const_int(bx.type_i1(), 0);
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Shouldn't this be called poison_on_zero, which we are then setting to false?

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hmmm, plausible. I was going for a "nah nah" instead of a "yeah nah".

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nikic commented May 21, 2024

@bors r=RalfJung,nikic

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bors commented May 21, 2024

📌 Commit 213351a has been approved by RalfJung,nikic

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 21, 2024
bors added a commit to rust-lang-ci/rust that referenced this pull request May 21, 2024
…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#124570 (Miscellaneous cleanups)
 - rust-lang#124772 (Refactor documentation for Apple targets)
 - rust-lang#125011 (Add opt-for-size core lib feature flag)
 - rust-lang#125218 (Migrate `run-make/no-intermediate-extras` to new `rmake.rs`)
 - rust-lang#125225 (Use functions from `crt_externs.h` on iOS/tvOS/watchOS/visionOS)
 - rust-lang#125266 (compiler: add simd_ctpop intrinsic)
 - rust-lang#125348 (Small fixes to `std::path::absolute` docs)

Failed merges:

 - rust-lang#125296 (Fix `unexpected_cfgs` lint on std)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit fd975f7 into rust-lang:master May 21, 2024
6 checks passed
@rustbot rustbot added this to the 1.80.0 milestone May 21, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request May 21, 2024
Rollup merge of rust-lang#125266 - workingjubilee:stream-plastic-love, r=RalfJung,nikic

compiler: add simd_ctpop intrinsic

Fairly straightforward addition.

cc `@rust-lang/opsem` new (extremely boring) intrinsic
@workingjubilee workingjubilee deleted the stream-plastic-love branch May 21, 2024 19:53
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9 participants