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Fix unnecessary error when using neon target feature #95044

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Fix unnecessary error when using neon target feature #95044

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2 changes: 1 addition & 1 deletion compiler/rustc_codegen_llvm/src/attributes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -325,7 +325,7 @@ pub fn from_fn_attrs<'ll, 'tcx>(

if let Some(f) = llvm_util::check_tied_features(
cx.tcx.sess,
&function_features.iter().map(|f| (*f, true)).collect(),
&mut function_features.iter().map(|f| (*f, true)).collect(),
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Doing &mut collection.iter().stuff().collect() seems like an anti-pattern to me; you're passing in a collection to be mutated, but immediately throwing it away? Its certainly not clear on the callee side that that is what you'll be doing.

I skimmed the source; it seems like all (two?) callsites are creating the hashmap and throwing it away after the call to llvm_util::check_tied_features.

If I'm correct and all call sites are indeed freshly creating the hashmap and immediately throwing it away, then I would either change check_tied_features to take the hashmap by value, or I'd revise the code for check_tied_features so that it doesn't need to modify the hashmap at all.

) {
let span = cx
.tcx
Expand Down
13 changes: 10 additions & 3 deletions compiler/rustc_codegen_llvm/src/llvm_util.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -217,8 +217,15 @@ pub fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> SmallVec<[&'a str; 2]
// ensure only valid combinations are allowed.
pub fn check_tied_features(
sess: &Session,
features: &FxHashMap<&str, bool>,
features: &mut FxHashMap<&str, bool>,
) -> Option<&'static [&'static str]> {
// neon implies fp, so we don't need to error in this case.
if sess.target.arch == "aarch64" && !features.contains_key("fp") {
if let Some(neon) = features.get("neon").copied() {
features.insert("fp", neon);
}
}

for tied in tied_target_features(sess) {
// Tied features must be set to the same value, or not set at all
let mut tied_iter = tied.iter();
Expand Down Expand Up @@ -487,8 +494,8 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str

if diagnostics {
// FIXME(nagisa): figure out how to not allocate a full hashset here.
let featmap = feats.iter().map(|&(flag, feat)| (feat, flag == '+')).collect();
if let Some(f) = check_tied_features(sess, &featmap) {
let mut featmap = feats.iter().map(|&(flag, feat)| (feat, flag == '+')).collect();
if let Some(f) = check_tied_features(sess, &mut featmap) {
sess.err(&format!(
"target features {} must all be enabled or disabled together",
f.join(", ")
Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/target-feature/tied-features-cli.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
// revisions: one two three
// revisions: one two three four five
// compile-flags: --crate-type=rlib --target=aarch64-unknown-linux-gnu
// needs-llvm-components: aarch64
//
Expand All @@ -11,6 +11,8 @@
// [three] compile-flags: -C target-feature=+paca,+pacg,-paca
// [four] build-pass
// [four] compile-flags: -C target-feature=-paca,+pacg -C target-feature=+paca
// [five] build-pass
// [five] compile-flags: -C target-feature=+neon
#![feature(no_core, lang_items)]
#![no_core]

Expand Down
5 changes: 4 additions & 1 deletion src/test/ui/target-feature/tied-features.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,17 +19,20 @@ pub fn main() {
bar();
baz();
inner();
implicit_fp();
}
}

#[target_feature(enable = "paca")]
//~^ ERROR must all be either enabled or disabled together
unsafe fn foo() {}


#[target_feature(enable = "paca,pacg")]
unsafe fn bar() {}

#[target_feature(enable = "paca")]
#[target_feature(enable = "pacg")]
unsafe fn baz() {}

#[target_feature(enable = "neon")]
unsafe fn implicit_fp() {}
2 changes: 1 addition & 1 deletion src/test/ui/target-feature/tied-features.stderr
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Expand Up @@ -7,7 +7,7 @@ LL | #[target_feature(enable = "pacg")]
= help: add the missing features in a `target_feature` attribute

error: the target features paca, pacg must all be either enabled or disabled together
--> $DIR/tied-features.rs:25:1
--> $DIR/tied-features.rs:26:1
|
LL | #[target_feature(enable = "paca")]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand Down