coverage. Add coverage-options=mcdc as gate for MC/DC instrument

compiler/rustc_interface/src/tests.rs

@@ -758,7 +758,7 @@ macro_rules! tracked {
     );
     tracked!(codegen_backend, Some("abc".to_string()));
     tracked!(collapse_macro_debuginfo, CollapseMacroDebuginfo::Yes);
-    tracked!(coverage_options, CoverageOptions { branch: true });
+    tracked!(coverage_options, CoverageOptions { branch: true, mcdc: true });
     tracked!(crate_attr, vec!["abc".to_string()]);
     tracked!(cross_crate_inline_threshold, InliningThreshold::Always);
     tracked!(debug_info_for_profiling, true);

compiler/rustc_mir_build/messages.ftl

@@ -97,6 +97,8 @@ mir_build_deref_raw_pointer_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
     .note = raw pointers may be null, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
     .label = dereference of raw pointer
 
+mir_build_exceeds_mcdc_condition_num_limit =  Conditions number of the decision ({$conditions_num}) exceeds limit ({$max_conditions_num}). MCDC analysis will not count this expression.
+
 mir_build_extern_static_requires_unsafe =
     use of extern static is unsafe and requires unsafe block
     .note = extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior

compiler/rustc_mir_build/src/errors.rs

@@ -818,6 +818,15 @@ pub struct NontrivialStructuralMatch<'tcx> {
     pub non_sm_ty: Ty<'tcx>,
 }
 
+#[derive(Diagnostic)]
+#[diag(mir_build_exceeds_mcdc_condition_num_limit)]
+pub(crate) struct MCDCExceedsConditionNumLimit {
+    #[primary_span]
+    pub span: Span,
+    pub conditions_num: usize,
+    pub max_conditions_num: usize,
+}
+
 #[derive(Diagnostic)]
 #[diag(mir_build_pattern_not_covered, code = E0005)]
 pub(crate) struct PatternNotCovered<'s, 'tcx> {

compiler/rustc_session/src/config.rs

@@ -148,6 +148,8 @@ pub enum InstrumentCoverage {
 pub struct CoverageOptions {
     /// Add branch coverage instrumentation.
     pub branch: bool,
+    /// Add mcdc coverage instrumentation.
+    pub mcdc: bool,
 }
 
 /// Settings for `-Z instrument-xray` flag.

compiler/rustc_session/src/options.rs

@@ -396,7 +396,7 @@ mod desc {
     pub const parse_optimization_fuel: &str = "crate=integer";
     pub const parse_dump_mono_stats: &str = "`markdown` (default) or `json`";
     pub const parse_instrument_coverage: &str = parse_bool;
-    pub const parse_coverage_options: &str = "`branch` or `no-branch`";
+    pub const parse_coverage_options: &str = "either  `no-branch`, `branch` or `mcdc`";
     pub const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
     pub const parse_unpretty: &str = "`string` or `string=string`";
     pub const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
@@ -946,17 +946,19 @@ pub(crate) fn parse_coverage_options(slot: &mut CoverageOptions, v: Option<&str>
         let Some(v) = v else { return true };
 
         for option in v.split(',') {
-            let (option, enabled) = match option.strip_prefix("no-") {
-                Some(without_no) => (without_no, false),
-                None => (option, true),
-            };
-            let slot = match option {
-                "branch" => &mut slot.branch,
+            match option {
+                "no-branch" => {
+                    slot.branch = false;
+                    slot.mcdc = false;
+                }
+                "branch" => slot.branch = true,
+                "mcdc" => {
+                    slot.branch = true;
+                    slot.mcdc = true;
+                }
                 _ => return false,
-            };
-            *slot = enabled;
+            }
         }
-
         true
     }
 

compiler/rustc_session/src/session.rs

@@ -352,6 +352,10 @@ pub fn instrument_coverage_branch(&self) -> bool {
         self.instrument_coverage() && self.opts.unstable_opts.coverage_options.branch
     }
 
+    pub fn instrument_coverage_mcdc(&self) -> bool {
+        self.instrument_coverage() && self.opts.unstable_opts.coverage_options.mcdc
+    }
+
     pub fn is_sanitizer_cfi_enabled(&self) -> bool {
         self.opts.unstable_opts.sanitizer.contains(SanitizerSet::CFI)
     }

src/doc/rustc/src/instrument-coverage.md

@@ -351,8 +351,8 @@ $ llvm-cov report \
 This unstable option provides finer control over some aspects of coverage
 instrumentation. Pass one or more of the following values, separated by commas.
 
-- `branch` or `no-branch`
-  - Enables or disables branch coverage instrumentation.
+- Either `no-branch`, `branch` or `mcdc`
+  - `branch` enables branch coverage instrumentation and `mcdc` further enables modified condition/decision coverage instrumentation. `no-branch` disables branch coverage instrumentation, which is same as do not pass `branch` or `mcdc`.
 
 ## Other references
 

src/doc/unstable-book/src/compiler-flags/coverage-options.md

@@ -5,4 +5,4 @@ This option controls details of the coverage instrumentation performed by
 
 Multiple options can be passed, separated by commas. Valid options are:
 
-- `branch` or `no-branch`: Enables or disables branch coverage instrumentation.
+- `no-branch`, `branch` or `mcdc`: `branch` enables branch coverage instrumentation and `mcdc` further enables modified condition/decision coverage instrumentation. `no-branch` disables branch coverage instrumentation as well as mcdc instrumentation, which is same as do not pass `branch` or `mcdc`.

tests/ui/instrument-coverage/coverage-options.bad.stderr

@@ -1,2 +1,2 @@
-error: incorrect value `bad` for unstable option `coverage-options` - `branch` or `no-branch` was expected
+error: incorrect value `bad` for unstable option `coverage-options` - either  `no-branch`, `branch` or `mcdc` was expected
 

tests/ui/instrument-coverage/coverage-options.rs

@@ -8,7 +8,13 @@
 //@ [no-branch] check-pass
 //@ [no-branch] compile-flags: -Zcoverage-options=no-branch
 
+//@ [mcdc] check-pass
+//@ [mcdc] compile-flags: -Zcoverage-options=mcdc
+
 //@ [bad] check-fail
 //@ [bad] compile-flags: -Zcoverage-options=bad
 
+//@ [conflict] check-fail
+//@ [conflict] compile-flags: -Zcoverage-options=no-branch,mcdc
+
 fn main() {}