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Auto merge of #84562 - richkadel:issue-83601, r=tmandry

Adds feature-gated `#[no_coverage]` function attribute, to fix derived Eq `0` coverage issue #83601

Derived Eq no longer shows uncovered

The Eq trait has a special hidden function. MIR `InstrumentCoverage`
would add this function to the coverage map, but it is never called, so
the `Eq` trait would always appear uncovered.

Fixes: #83601

The fix required creating a new function attribute `no_coverage` to mark
functions that should be ignored by `InstrumentCoverage` and the
coverage `mapgen` (during codegen).

Adding a `no_coverage` feature gate with tracking issue #84605.

r? `@tmandry`
cc: `@wesleywiser`
This commit is contained in:
bors 2021-04-28 13:05:16 +00:00
commit 20040fa332
18 changed files with 198 additions and 2 deletions

View file

@ -16,9 +16,19 @@ pub fn expand_deriving_eq(
push: &mut dyn FnMut(Annotatable),
) {
let inline = cx.meta_word(span, sym::inline);
let no_coverage_ident =
rustc_ast::attr::mk_nested_word_item(Ident::new(sym::no_coverage, span));
let no_coverage_feature =
rustc_ast::attr::mk_list_item(Ident::new(sym::feature, span), vec![no_coverage_ident]);
let no_coverage = cx.meta_word(span, sym::no_coverage);
let hidden = rustc_ast::attr::mk_nested_word_item(Ident::new(sym::hidden, span));
let doc = rustc_ast::attr::mk_list_item(Ident::new(sym::doc, span), vec![hidden]);
let attrs = vec![cx.attribute(inline), cx.attribute(doc)];
let attrs = vec![
cx.attribute(inline),
cx.attribute(no_coverage_feature),
cx.attribute(no_coverage),
cx.attribute(doc),
];
let trait_def = TraitDef {
span,
attributes: Vec::new(),

View file

@ -8,6 +8,7 @@ use rustc_codegen_ssa::traits::{ConstMethods, CoverageInfoMethods};
use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
use rustc_hir::def_id::{DefId, DefIdSet, LOCAL_CRATE};
use rustc_llvm::RustString;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use rustc_middle::mir::coverage::CodeRegion;
use rustc_span::Symbol;
@ -280,6 +281,10 @@ fn add_unused_functions<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
let mut unused_def_ids_by_file: FxHashMap<Symbol, Vec<DefId>> = FxHashMap::default();
for &non_codegenned_def_id in all_def_ids.difference(codegenned_def_ids) {
let codegen_fn_attrs = tcx.codegen_fn_attrs(non_codegenned_def_id);
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_COVERAGE) {
continue;
}
// Make sure the non-codegenned (unused) function has a file_name
if let Some(non_codegenned_file_name) = tcx.covered_file_name(non_codegenned_def_id) {
let def_ids =

View file

@ -646,6 +646,10 @@ declare_features! (
/// Allows `extern "wasm" fn`
(active, wasm_abi, "1.53.0", Some(83788), None),
/// Allows function attribute `#[no_coverage]`, to bypass coverage
/// instrumentation of that function.
(active, no_coverage, "1.53.0", Some(84605), None),
/// Allows trait bounds in `const fn`.
(active, const_fn_trait_bound, "1.53.0", Some(57563), None),

View file

@ -273,6 +273,13 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
template!(List: "address, memory, thread"),
experimental!(no_sanitize)
),
ungated!(
// Not exclusively gated at the crate level (though crate-level is
// supported). The feature can alternatively be enabled on individual
// functions.
no_coverage, AssumedUsed,
template!(Word),
),
// FIXME: #14408 assume docs are used since rustdoc looks at them.
ungated!(doc, AssumedUsed, template!(List: "hidden|inline|...", NameValueStr: "string")),

View file

@ -89,6 +89,10 @@ bitflags! {
/// #[cmse_nonsecure_entry]: with a TrustZone-M extension, declare a
/// function as an entry function from Non-Secure code.
const CMSE_NONSECURE_ENTRY = 1 << 14;
/// `#[no_coverage]`: indicates that the function should be ignored by
/// the MIR `InstrumentCoverage` pass and not added to the coverage map
/// during codegen.
const NO_COVERAGE = 1 << 15;
}
}

View file

@ -23,6 +23,7 @@ use rustc_index::vec::IndexVec;
use rustc_middle::hir;
use rustc_middle::hir::map::blocks::FnLikeNode;
use rustc_middle::ich::StableHashingContext;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use rustc_middle::mir::coverage::*;
use rustc_middle::mir::{
self, BasicBlock, BasicBlockData, Coverage, SourceInfo, Statement, StatementKind, Terminator,
@ -87,6 +88,11 @@ impl<'tcx> MirPass<'tcx> for InstrumentCoverage {
_ => {}
}
let codegen_fn_attrs = tcx.codegen_fn_attrs(mir_source.def_id());
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NO_COVERAGE) {
return;
}
trace!("InstrumentCoverage starting for {:?}", mir_source.def_id());
Instrumentor::new(&self.name(), tcx, mir_body).inject_counters();
trace!("InstrumentCoverage starting for {:?}", mir_source.def_id());

View file

@ -781,6 +781,7 @@ symbols! {
no,
no_builtins,
no_core,
no_coverage,
no_crate_inject,
no_debug,
no_default_passes,

View file

@ -2661,6 +2661,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
let mut inline_span = None;
let mut link_ordinal_span = None;
let mut no_sanitize_span = None;
let mut no_coverage_feature_enabled = false;
let mut no_coverage_attr = None;
for attr in attrs.iter() {
if tcx.sess.check_name(attr, sym::cold) {
codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
@ -2724,6 +2726,15 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
codegen_fn_attrs.flags |= CodegenFnAttrFlags::NAKED;
} else if tcx.sess.check_name(attr, sym::no_mangle) {
codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
} else if attr.has_name(sym::feature) {
if let Some(list) = attr.meta_item_list() {
if list.iter().any(|nested_meta_item| nested_meta_item.has_name(sym::no_coverage)) {
tcx.sess.mark_attr_used(attr);
no_coverage_feature_enabled = true;
}
}
} else if tcx.sess.check_name(attr, sym::no_coverage) {
no_coverage_attr = Some(attr);
} else if tcx.sess.check_name(attr, sym::rustc_std_internal_symbol) {
codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
} else if tcx.sess.check_name(attr, sym::used) {
@ -2934,6 +2945,23 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
}
}
if let Some(no_coverage_attr) = no_coverage_attr {
if tcx.sess.features_untracked().no_coverage || no_coverage_feature_enabled {
codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_COVERAGE
} else {
let mut err = feature_err(
&tcx.sess.parse_sess,
sym::no_coverage,
no_coverage_attr.span,
"the `#[no_coverage]` attribute is an experimental feature",
);
if tcx.sess.parse_sess.unstable_features.is_nightly_build() {
err.help("or, alternatively, add `#[feature(no_coverage)]` to the function");
}
err.emit();
}
}
codegen_fn_attrs.inline = attrs.iter().fold(InlineAttr::None, |ia, attr| {
if !attr.has_name(sym::inline) {
return ia;