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: https://github.com/rust-lang/compiler-team/issues/866
Closes: https://github.com/rust-lang/compiler-team/issues/866

[1]: https://github.com/rust-lang/rust/blob/555e1d0386f024a8359645c3217f4b3eae9be042/library/std/build.rs#L84-L186

1 files changed, 4 insertions, 4 deletions

diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index b2feeacdb46..e8010ec9fc4 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -29,7 +29,7 @@ use back::owned_target_machine::OwnedTargetMachine;
 use back::write::{create_informational_target_machine, create_target_machine};
 use context::SimpleCx;
 use errors::{AutoDiffWithoutLTO, ParseTargetMachineConfig};
-use llvm_util::target_features_cfg;
+use llvm_util::target_config;
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_codegen_ssa::back::lto::{LtoModuleCodegen, SerializedModule, ThinModule};
@@ -37,7 +37,7 @@ use rustc_codegen_ssa::back::write::{
     CodegenContext, FatLtoInput, ModuleConfig, TargetMachineFactoryConfig, TargetMachineFactoryFn,
 };
 use rustc_codegen_ssa::traits::*;
-use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen};
+use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen, TargetConfig};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::{DiagCtxtHandle, FatalError};
 use rustc_metadata::EncodedMetadata;
@@ -338,8 +338,8 @@ impl CodegenBackend for LlvmCodegenBackend {
         llvm_util::print_version();
     }
 
-    fn target_features_cfg(&self, sess: &Session) -> (Vec<Symbol>, Vec<Symbol>) {
-        target_features_cfg(sess)
+    fn target_config(&self, sess: &Session) -> TargetConfig {
+        target_config(sess)
     }
 
     fn codegen_crate<'tcx>(