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adjust GCC backend
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@RalfJung
RalfJung committed Dec 26, 2024
1 parent f6c5f0c commit 30137ec
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Showing 2 changed files with 114 additions and 81 deletions.
1 change: 1 addition & 0 deletions compiler/rustc_codegen_gcc/src/errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ pub(crate) struct UnstableCTargetFeature<'a> {
#[diag(codegen_gcc_forbidden_ctarget_feature)]
pub(crate) struct ForbiddenCTargetFeature<'a> {
pub feature: &'a str,
pub enabled: &'a str,
pub reason: &'a str,
}

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194 changes: 113 additions & 81 deletions compiler/rustc_codegen_gcc/src/gcc_util.rs
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Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
use std::iter::FromIterator;

#[cfg(feature = "master")]
use gccjit::Context;
use rustc_codegen_ssa::codegen_attrs::check_tied_features;
use rustc_codegen_ssa::errors::TargetFeatureDisableOrEnable;
use rustc_data_structures::fx::FxHashMap;
use rustc_middle::bug;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::unord::UnordSet;
use rustc_session::Session;
use rustc_target::target_features::RUSTC_SPECIFIC_FEATURES;
use smallvec::{SmallVec, smallvec};
Expand Down Expand Up @@ -37,82 +39,128 @@ pub(crate) fn global_gcc_features(sess: &Session, diagnostics: bool) -> Vec<Stri
let mut features = vec![];

// Features implied by an implicit or explicit `--target`.
features.extend(
sess.target
.features
.split(',')
.filter(|v| !v.is_empty() && backend_feature_name(v).is_some())
.map(String::from),
);
features.extend(sess.target.features.split(',').filter(|v| !v.is_empty()).map(String::from));

// -Ctarget-features
let known_features = sess.target.rust_target_features();
let mut featsmap = FxHashMap::default();
let feats = sess
.opts
.cg
.target_feature
.split(',')
.filter_map(|s| {
let enable_disable = match s.chars().next() {
None => return None,
Some(c @ ('+' | '-')) => c,
Some(_) => {
if diagnostics {
sess.dcx().emit_warn(UnknownCTargetFeaturePrefix { feature: s });
}
return None;
}
};

// Get the backend feature name, if any.
// This excludes rustc-specific features, that do not get passed down to GCC.
let feature = backend_feature_name(s)?;
// Warn against use of GCC specific feature names on the CLI.
// Ensure that all ABI-required features are enabled, and the ABI-forbidden ones
// are disabled.
let (abi_enable, abi_disable) = sess.target.abi_required_features();
let abi_enable_set = FxHashSet::from_iter(abi_enable.iter().copied());
let abi_disable_set = FxHashSet::from_iter(abi_disable.iter().copied());

// Compute implied features
let mut all_rust_features = vec![];
for feature in sess.opts.cg.target_feature.split(',') {
if let Some(feature) = feature.strip_prefix('+') {
all_rust_features.extend(
UnordSet::from(sess.target.implied_target_features(std::iter::once(feature)))
.to_sorted_stable_ord()
.iter()
.map(|&&s| (true, s)),
)
} else if let Some(feature) = feature.strip_prefix('-') {
// FIXME: Why do we not remove implied features on "-" here?
// We do the equivalent above in `target_features_cfg`.
// See <https://github.com/rust-lang/rust/issues/134792>.
all_rust_features.push((false, feature));
} else if !feature.is_empty() {
if diagnostics {
let feature_state = known_features.iter().find(|&&(v, _, _)| v == feature);
match feature_state {
None => {
let rust_feature =
known_features.iter().find_map(|&(rust_feature, _, _)| {
let gcc_features = to_gcc_features(sess, rust_feature);
if gcc_features.contains(&feature)
&& !gcc_features.contains(&rust_feature)
{
Some(rust_feature)
} else {
None
}
});
let unknown_feature = if let Some(rust_feature) = rust_feature {
UnknownCTargetFeature {
feature,
rust_feature: PossibleFeature::Some { rust_feature },
}
} else {
UnknownCTargetFeature { feature, rust_feature: PossibleFeature::None }
};
sess.dcx().emit_warn(unknown_feature);
}
Some((_, stability, _)) => {
if let Err(reason) =
stability.toggle_allowed(&sess.target, enable_disable == '+')
sess.dcx().emit_warn(UnknownCTargetFeaturePrefix { feature });
}
}
}
// Remove features that are meant for rustc, not LLVM.
all_rust_features.retain(|(_, feature)| {
// Retain if it is not a rustc feature
!RUSTC_SPECIFIC_FEATURES.contains(feature)
});

// Check feature validity.
if diagnostics {
for &(enable, feature) in &all_rust_features {
let feature_state = known_features.iter().find(|&&(v, _, _)| v == feature);
match feature_state {
None => {
let rust_feature = known_features.iter().find_map(|&(rust_feature, _, _)| {
let gcc_features = to_gcc_features(sess, rust_feature);
if gcc_features.contains(&feature) && !gcc_features.contains(&rust_feature)
{
sess.dcx().emit_warn(ForbiddenCTargetFeature { feature, reason });
} else if stability.requires_nightly().is_some() {
// An unstable feature. Warn about using it. (It makes little sense
// to hard-error here since we just warn about fully unknown
// features above).
sess.dcx().emit_warn(UnstableCTargetFeature { feature });
Some(rust_feature)
} else {
None
}
});
let unknown_feature = if let Some(rust_feature) = rust_feature {
UnknownCTargetFeature {
feature,
rust_feature: PossibleFeature::Some { rust_feature },
}
} else {
UnknownCTargetFeature { feature, rust_feature: PossibleFeature::None }
};
sess.dcx().emit_warn(unknown_feature);
}
Some((_, stability, _)) => {
if let Err(reason) = stability.toggle_allowed() {
sess.dcx().emit_warn(ForbiddenCTargetFeature {
feature,
enabled: if enable { "enabled" } else { "disabled" },
reason,
});
} else if stability.requires_nightly().is_some() {
// An unstable feature. Warn about using it. (It makes little sense
// to hard-error here since we just warn about fully unknown
// features above).
sess.dcx().emit_warn(UnstableCTargetFeature { feature });
}
}
}

// FIXME(nagisa): figure out how to not allocate a full hashset here.
featsmap.insert(feature, enable_disable == '+');
// Ensure that the features we enable/disable are compatible with the ABI.
if enable {
if abi_disable_set.contains(feature) {
sess.dcx().emit_warn(ForbiddenCTargetFeature {
feature,
enabled: "enabled",
reason: "this feature is incompatible with the target ABI",
});
}
} else {
if abi_enable_set.contains(feature) {
sess.dcx().emit_warn(ForbiddenCTargetFeature {
feature,
enabled: "disabled",
reason: "this feature is required by the target ABI",
});
}
}

// ... otherwise though we run through `to_gcc_features` when
// FIXME(nagisa): figure out how to not allocate a full hashset here.
featsmap.insert(feature, enable);
}
}

// To be sure the ABI-relevant features are all in the right state, we explicitly
// (un)set them here. This means if the target spec sets those features wrong,
// we will silently correct them rather than silently producing wrong code.
// (The target sanity check tries to catch this, but we can't know which features are
// enabled in GCC by default so we can't be fully sure about that check.)
for feature in abi_enable {
all_rust_features.push((true, feature));
}
for feature in abi_disable {
all_rust_features.push((false, feature));
}

// Translate this into GCC features.
let feats = all_rust_features
.iter()
.filter_map(|&(enable, feature)| {
let enable_disable = if enable { '+' } else { '-' };
// We run through `to_gcc_features` when
// passing requests down to GCC. This means that all in-language
// features also work on the command line instead of having two
// different names when the GCC name and the Rust name differ.
Expand Down Expand Up @@ -146,22 +194,6 @@ pub(crate) fn global_gcc_features(sess: &Session, diagnostics: bool) -> Vec<Stri
features
}

/// Returns a feature name for the given `+feature` or `-feature` string.
///
/// Only allows features that are backend specific (i.e. not [`RUSTC_SPECIFIC_FEATURES`].)
fn backend_feature_name(s: &str) -> Option<&str> {
// features must start with a `+` or `-`.
let feature = s.strip_prefix(&['+', '-'][..]).unwrap_or_else(|| {
bug!("target feature `{}` must begin with a `+` or `-`", s);
});
// Rustc-specific feature requests like `+crt-static` or `-crt-static`
// are not passed down to GCC.
if RUSTC_SPECIFIC_FEATURES.contains(&feature) {
return None;
}
Some(feature)
}

// To find a list of GCC's names, check https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
pub fn to_gcc_features<'a>(sess: &Session, s: &'a str) -> SmallVec<[&'a str; 2]> {
let arch = if sess.target.arch == "x86_64" { "x86" } else { &*sess.target.arch };
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