Introduce -C instrument-coverage=branch to gate branch coverage

Author: Swatinem

compiler/rustc_session/src/config.rs

@@ -168,6 +168,8 @@ pub enum MirSpanview {
 pub enum InstrumentCoverage {
     /// Default `-C instrument-coverage` or `-C instrument-coverage=statement`
     All,
+    /// Additionally, instrument branches and output branch overage
+    Branch,
     /// `-Zunstable-options -C instrument-coverage=except-unused-generics`
     ExceptUnusedGenerics,
     /// `-Zunstable-options -C instrument-coverage=except-unused-functions`

compiler/rustc_session/src/options.rs

@@ -382,7 +382,7 @@ mod desc {
     pub const parse_mir_spanview: &str = "`statement` (default), `terminator`, or `block`";
     pub const parse_dump_mono_stats: &str = "`markdown` (default) or `json`";
     pub const parse_instrument_coverage: &str =
-        "`all` (default), `except-unused-generics`, `except-unused-functions`, or `off`";
+        "`all` (default), `branch`, `except-unused-generics`, `except-unused-functions`, or `off`";
     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 number bigger than 0";
@@ -895,6 +895,7 @@ mod parse {
 
         *slot = Some(match v {
             "all" => InstrumentCoverage::All,
+            "branch" => InstrumentCoverage::Branch,
             "except-unused-generics" | "except_unused_generics" => {
                 InstrumentCoverage::ExceptUnusedGenerics
             }
@@ -1299,6 +1300,7 @@ options! {
         reports (note, the compiler build config must include `profiler = true`); \
         implies `-C symbol-mangling-version=v0`. Optional values are:
         `=all` (implicit value)
+        `=branch`
         `=except-unused-generics`
         `=except-unused-functions`
         `=off` (default)"),
@@ -1547,6 +1549,7 @@ options! {
         reports (note, the compiler build config must include `profiler = true`); \
         implies `-C symbol-mangling-version=v0`. Optional values are:
         `=all` (implicit value)
+        `=branch`
         `=except-unused-generics`
         `=except-unused-functions`
         `=off` (default)"),

compiler/rustc_session/src/session.rs

@@ -695,6 +695,10 @@ impl Session {
         self.opts.cg.instrument_coverage() != InstrumentCoverage::Off
     }
 
+    pub fn instrument_coverage_branch(&self) -> bool {
+        self.opts.cg.instrument_coverage() == InstrumentCoverage::Branch
+    }
+
     pub fn instrument_coverage_except_unused_generics(&self) -> bool {
         self.opts.cg.instrument_coverage() == InstrumentCoverage::ExceptUnusedGenerics
     }