diff options
| -rw-r--r-- | compiler/rustc_target/src/target_features.rs | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/compiler/rustc_target/src/target_features.rs b/compiler/rustc_target/src/target_features.rs index b649610b391..a313baf6066 100644 --- a/compiler/rustc_target/src/target_features.rs +++ b/compiler/rustc_target/src/target_features.rs @@ -39,7 +39,7 @@ pub enum Stability<Toggleability> { allow_toggle: Toggleability, }, /// This feature can not be set via `-Ctarget-feature` or `#[target_feature]`, it can only be - /// set in the basic target definition. It is never set in `cfg(target_feature)`. Used in + /// set in the target spec. It is never set in `cfg(target_feature)`. Used in /// particular for features that change the floating-point ABI. Forbidden { reason: &'static str }, } @@ -600,7 +600,8 @@ const RISCV_FEATURES: &[(&str, StabilityUncomputed, ImpliedFeatures)] = &[ Err("feature is required by ABI") } "ilp32e" if enable => { - // The `d` feature apparently is incompatible with this ABI. + // ilp32e is incompatible with features that need aligned load/stores > 32 bits, + // like `d`. Err("feature is incompatible with ABI") } _ => Ok(()), @@ -618,7 +619,10 @@ const RISCV_FEATURES: &[(&str, StabilityUncomputed, ImpliedFeatures)] = &[ allow_toggle: |target, enable| { match &*target.llvm_abiname { _ if !enable => { - // This is a negative feature, *disabling* it is always okay. + // Disabling this feature means we can use more registers (x16-x31). + // The "e" ABIs treat them as caller-save, so it is safe to use them only + // in some parts of a program while the rest doesn't know they even exist. + // On other ABIs, the feature is already disabled anyway. Ok(()) } "ilp32e" | "lp64e" => { |