Implement the internal feature `cfg_target_has_reliable_f16_f128` #140323

tgross35 · 2025-04-26T05:09:41Z

Support for f16 and f128 is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable.

Introduce the cfg_target_has_reliable_f16_f128 internal feature, which provides the following new configuration gates:

cfg(target_has_reliable_f16)
cfg(target_has_reliable_f16_math)
cfg(target_has_reliable_f128)
cfg(target_has_reliable_f128_math)

reliable_f16 and reliable_f128 indicate that basic arithmetic for the type works correctly. The _math versions indicate that anything relying on libm works correctly, since sometimes this hits a separate class of codegen bugs.

These options match configuration set by the build script at 1. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up.

The config introduced here is not planned to ever become stable, it is only intended to replace the build scripts for std tests and compiler-builtins that don't have any way to configure based on the codegen backend.

MCP: rust-lang/compiler-team#866
Closes: rust-lang/compiler-team#866

The second commit makes use of this config to replace cfg_{f16,f128}{,_math} in library/. I omitted providing a cfg(bootstrap) configuration to keep things simpler since the next beta branch is in two weeks.

try-job: aarch64-gnu
try-job: i686-msvc-1
try-job: test-various
try-job: x86_64-gnu
try-job: x86_64-msvc-ext2

r? @ghost

tgross35 · 2025-04-26T06:21:28Z

@bors try

Implement the internal feature `cfg_target_has_reliable_f16_f128` Support for `f16` and `f128` is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable. Introduce the `target_has_reliable_f16_f128` configuration option, gated behind `cfg_target_has_reliable_f16_f128`, as an indicator for whether or not the backend supports these types to a point that they can and should be tested. The configuration mostly follows the logic used by `target_feature`, and similarly takes a value: #[cfg(target_has_reliable_f16_f128 = "f16")] Accepted values are: * `f16` * `f16-math` * `f128` * `f128-math` `f16` and `f128` indicate that basic arithmetic for the type works correctly. The `-math` versions indicate that anything relying on `libm` works correctly, since sometimes this hits a separate class of codegen bugs. These options match configuration set by the build script at [1]. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up. The config introduced here is not intended to ever become stable, it is only intended to replace the build scripts for `std` tests and in `compiler-builtins` that don't have any way to set configuration based on the codegen backend. MCP: rust-lang/compiler-team#866 Closes: rust-lang/compiler-team#866 [1]: https://github.com/rust-lang/rust/blob/555e1d0386f024a8359645c3217f4b3eae9be042/library/std/build.rs#L84-L186 --- The second commit makes use of this config to replace `cfg_{f16,f128}{,_math}` in `library/`. try-job: aarch64-gnu try-job: i686-msvc-1 try-job: test-various try-job: x86_64-gnu try-job: x86_64-msvc-ext2

bors · 2025-04-26T06:22:39Z

⌛ Trying commit e7fb9c5 with merge 4055b73...

rustbot · 2025-04-26T06:42:48Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred in cfg and check-cfg configuration

cc @Urgau

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

tgross35 · 2025-04-26T06:43:52Z

r? compiler

Cc @bjorn3 @antoyo since this touches the backend interfaces.

compiler/rustc_session/src/config/cfg.rs

rustbot · 2025-04-26T07:16:54Z

Some changes occurred in src/doc/rustc/src/check-cfg.md

cc @Urgau

tgross35 · 2025-04-26T07:30:51Z

Hm... I think I'm actually leaning toward four separate key-only cfg options here rather than a single key with multiple values. I don't think the current version works as-well, it's a bit bulky and redundant with f16_f128 in the name.

Will change it over tomorrow unless anyone has a stronger preference.

@rustbot author

rustbot · 2025-04-26T07:30:55Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

tgross35 · 2025-04-26T20:26:42Z

Changed so this is split across four different cfg options.

@rustbot review

compiler/rustc_session/src/config/cfg.rs

src/doc/rustc/src/check-cfg.md

tests/ui/float/target-has-reliable-nightly-float.rs

compiler/rustc_session/src/config/cfg.rs

tgross35 · 2025-04-27T17:44:06Z

Since you have already started taking a look,

r? @Urgau

tgross35 · 2025-04-28T20:07:57Z

Thanks!

@bors r=Urgau

bors · 2025-04-28T20:07:59Z

📌 Commit dfa972e has been approved by Urgau

It is now in the queue for this repository.

Implement the internal feature `cfg_target_has_reliable_f16_f128` Support for `f16` and `f128` is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable. Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which provides the following new configuration gates: * `cfg(target_has_reliable_f16)` * `cfg(target_has_reliable_f16_math)` * `cfg(target_has_reliable_f128)` * `cfg(target_has_reliable_f128_math)` `reliable_f16` and `reliable_f128` indicate that basic arithmetic for the type works correctly. The `_math` versions indicate that anything relying on `libm` works correctly, since sometimes this hits a separate class of codegen bugs. These options match configuration set by the build script at [1]. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up. The config introduced here is not planned to ever become stable, it is only intended to replace the build scripts for `std` tests and `compiler-builtins` that don't have any way to configure based on the codegen backend. MCP: rust-lang/compiler-team#866 Closes: rust-lang/compiler-team#866 [1]: https://github.com/rust-lang/rust/blob/555e1d0386f024a8359645c3217f4b3eae9be042/library/std/build.rs#L84-L186 --- The second commit makes use of this config to replace `cfg_{f16,f128}{,_math}` in `library/`. I omitted providing a `cfg(bootstrap)` configuration to keep things simpler since the next beta branch is in two weeks. try-job: aarch64-gnu try-job: i686-msvc-1 try-job: test-various try-job: x86_64-gnu try-job: x86_64-msvc-ext2

WaffleLapkin · 2025-04-28T20:26:41Z

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -50,8 +50,15 @@ pub trait CodegenBackend {
    /// - The second is like the first, but also includes unstable features.
    ///
    /// RUSTC_SPECIFIC_FEATURES should be skipped here, those are handled outside codegen.
-    fn target_features_cfg(&self, _sess: &Session) -> (Vec<Symbol>, Vec<Symbol>) {
-        (vec![], vec![])
+    fn target_config(&self, _sess: &Session) -> TargetConfig {


Documentation of this function is outdated.

Also, why are the defaults true?

Thanks for the documentation catch. Since the rollup is already testing, I'll fix this in a follow up.

true is the default since eventually we'll need to get there on (hopefully) all backends for the types to stabilize. It seemed better to make other backends explicitly ack that they don't support the type, than to quietly be skipping all f16/f128 tests and get a surprise when we go to delete this feature and stabilize.

…enton Rollup of 9 pull requests Successful merges: - rust-lang#139308 (add autodiff inline) - rust-lang#140276 (Do not compute type_of for impl item if impl where clauses are unsatisfied) - rust-lang#140302 (Move inline asm check to typeck, properly handle aliases) - rust-lang#140323 (Implement the internal feature `cfg_target_has_reliable_f16_f128`) - rust-lang#140374 (Resolve instance for SymFn in global/naked asm) - rust-lang#140391 (Rename sub_ptr to offset_from_unsigned in docs) - rust-lang#140394 (Make bootstrap git tests more self-contained) - rust-lang#140396 (Workaround for windows-gnu rust-lld test failure) - rust-lang#140402 (only return nested goals for `Certainty::Yes`) r? `@ghost` `@rustbot` modify labels: rollup

Implement the internal feature `cfg_target_has_reliable_f16_f128` Support for `f16` and `f128` is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable. Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which provides the following new configuration gates: * `cfg(target_has_reliable_f16)` * `cfg(target_has_reliable_f16_math)` * `cfg(target_has_reliable_f128)` * `cfg(target_has_reliable_f128_math)` `reliable_f16` and `reliable_f128` indicate that basic arithmetic for the type works correctly. The `_math` versions indicate that anything relying on `libm` works correctly, since sometimes this hits a separate class of codegen bugs. These options match configuration set by the build script at [1]. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up. The config introduced here is not planned to ever become stable, it is only intended to replace the build scripts for `std` tests and `compiler-builtins` that don't have any way to configure based on the codegen backend. MCP: rust-lang/compiler-team#866 Closes: rust-lang/compiler-team#866 [1]: https://github.com/rust-lang/rust/blob/555e1d0386f024a8359645c3217f4b3eae9be042/library/std/build.rs#L84-L186 --- The second commit makes use of this config to replace `cfg_{f16,f128}{,_math}` in `library/`. I omitted providing a `cfg(bootstrap)` configuration to keep things simpler since the next beta branch is in two weeks. try-job: aarch64-gnu try-job: i686-msvc-1 try-job: test-various try-job: x86_64-gnu try-job: x86_64-msvc-ext2

…enton Rollup of 10 pull requests Successful merges: - rust-lang#139308 (add autodiff inline) - rust-lang#139656 (Stabilize `slice_as_chunks` library feature) - rust-lang#140022 (allow deref patterns to move out of boxes) - rust-lang#140276 (Do not compute type_of for impl item if impl where clauses are unsatisfied) - rust-lang#140302 (Move inline asm check to typeck, properly handle aliases) - rust-lang#140323 (Implement the internal feature `cfg_target_has_reliable_f16_f128`) - rust-lang#140391 (Rename sub_ptr to offset_from_unsigned in docs) - rust-lang#140394 (Make bootstrap git tests more self-contained) - rust-lang#140396 (Workaround for windows-gnu rust-lld test failure) - rust-lang#140402 (only return nested goals for `Certainty::Yes`) Failed merges: - rust-lang#139765 ([beta] Delay `hash_extract_if` stabilization from 1.87 to 1.88) r? `@ghost` `@rustbot` modify labels: rollup

…enton Rollup of 10 pull requests Successful merges: - rust-lang#139308 (add autodiff inline) - rust-lang#139656 (Stabilize `slice_as_chunks` library feature) - rust-lang#140022 (allow deref patterns to move out of boxes) - rust-lang#140276 (Do not compute type_of for impl item if impl where clauses are unsatisfied) - rust-lang#140302 (Move inline asm check to typeck, properly handle aliases) - rust-lang#140323 (Implement the internal feature `cfg_target_has_reliable_f16_f128`) - rust-lang#140391 (Rename sub_ptr to offset_from_unsigned in docs) - rust-lang#140394 (Make bootstrap git tests more self-contained) - rust-lang#140396 (Workaround for windows-gnu rust-lld test failure) - rust-lang#140402 (only return nested goals for `Certainty::Yes`) r? `@ghost` `@rustbot` modify labels: rollup

[experiment] reliable float experiments Trying a few blocked things based on top of rust-lang#140323. r? `@ghost` try-job: aarch64-gnu try-job: i686-gnu-1 try-job: i686-msvc-1 try-job: test-various try-job: x86_64-gnu try-job: x86_64-msvc-ext2

[experiment] reliable float experiments Trying a few blocked things based on top of rust-lang#140323. r? `@ghost` try-job: x86_64-gnu-llvm-19-1 try-job: x86_64-gnu-llvm-20-1

[experiment] reliable float experiments Trying a few blocked things based on top of rust-lang#140323. r? `@ghost` try-job: aarch64-gnu try-job: i686-gnu-1 try-job: i686-msvc-1 try-job: test-various try-job: x86_64-gnu try-job: x86_64-msvc-ext2 try-job: x86_64-gnu-llvm-19-1 try-job: x86_64-gnu-llvm-20-1

Rollup merge of rust-lang#140323 - tgross35:cfg-unstable-float, r=Urgau Implement the internal feature `cfg_target_has_reliable_f16_f128` Support for `f16` and `f128` is varied across targets, backends, and backend versions. Eventually we would like to reach a point where all backends support these approximately equally, but until then we have to work around some of these nuances of support being observable. Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which provides the following new configuration gates: * `cfg(target_has_reliable_f16)` * `cfg(target_has_reliable_f16_math)` * `cfg(target_has_reliable_f128)` * `cfg(target_has_reliable_f128_math)` `reliable_f16` and `reliable_f128` indicate that basic arithmetic for the type works correctly. The `_math` versions indicate that anything relying on `libm` works correctly, since sometimes this hits a separate class of codegen bugs. These options match configuration set by the build script at [1]. The logic for LLVM support is duplicated as-is from the same script. There are a few possible updates that will come as a follow up. The config introduced here is not planned to ever become stable, it is only intended to replace the build scripts for `std` tests and `compiler-builtins` that don't have any way to configure based on the codegen backend. MCP: rust-lang/compiler-team#866 Closes: rust-lang/compiler-team#866 [1]: https://github.com/rust-lang/rust/blob/555e1d0386f024a8359645c3217f4b3eae9be042/library/std/build.rs#L84-L186 --- The second commit makes use of this config to replace `cfg_{f16,f128}{,_math}` in `library/`. I omitted providing a `cfg(bootstrap)` configuration to keep things simpler since the next beta branch is in two weeks. try-job: aarch64-gnu try-job: i686-msvc-1 try-job: test-various try-job: x86_64-gnu try-job: x86_64-msvc-ext2

This was missed as part of [1]. [1]: rust-lang#140323

…, r=jieyouxu Update documentation for `fn target_config` This was missed as part of [1]. [1]: rust-lang#140323

Rollup merge of rust-lang#140432 - tgross35:target-config-docs-update, r=jieyouxu Update documentation for `fn target_config` This was missed as part of [1]. [1]: rust-lang#140323

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Rollup of 9 pull requests #140411

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Tracking Issue for f16 and f128 float types #116909

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Rollup of 10 pull requests #140414

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Rollup of 10 pull requests #140415

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[experiment] reliable float experiments #140424

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Update documentation for fn target_config

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This was missed as part of [1]. [1]: rust-lang#140323

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Update documentation for fn target_config #140432

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Rollup merge of rust-lang#140432 - tgross35:target-config-docs-update…

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…, r=jieyouxu Update documentation for `fn target_config` This was missed as part of [1]. [1]: rust-lang#140323

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Rust-gpu main fails to build Rust-GPU/rust-gpu#242

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Rollup merge of rust-lang#140432 - tgross35:target-config-docs-update…

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…, r=jieyouxu Update documentation for `fn target_config` This was missed as part of [1]. [1]: rust-lang#140323

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Implement the internal feature `cfg_target_has_reliable_f16_f128` #140323

Implement the internal feature `cfg_target_has_reliable_f16_f128` #140323

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Implement the internal feature cfg_target_has_reliable_f16_f128 #140323

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Implement the internal feature `cfg_target_has_reliable_f16_f128` #140323

Implement the internal feature `cfg_target_has_reliable_f16_f128` #140323

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