Auto merge of #114843 - Zalathar:test-coverage-map, r=oli-obk

coverage: Explicitly test the coverage maps produced by codegen/LLVM

Our existing coverage tests verify the output of end-to-end coverage reports, but we don't have any way to test the specific mapping information (code regions and their associated counters) that are emitted by `rustc_codegen_llvm` and LLVM. That makes it harder to to be confident in changes that would modify those mappings (whether deliberately or accidentally).

This PR addresses that by adding a new `coverage-map` test suite that does the following:
- Compiles test files to LLVM IR assembly (`.ll`)
- Feeds those IR files to a custom tool (`src/tools/coverage-dump`) that extracts and decodes coverage mappings, and prints them in a more human-readable format
- Checks the output of that tool against known-good snapshots

---

I recommend excluding the last commit while reviewing the main changes, because that last commit is just ~40 test files copied over from `tests/run-coverage`, plus their blessed coverage-map snapshots and a readme file. Those snapshots aren't really intended to be checked by hand; they're mostly there to increase the chances that an unintended change to coverage maps will be observable (even if it requires relatively specific circumstances to manifest).

3 files changed, 18 insertions, 1 deletions

diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index b3666192853..a24a6a4636d 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -703,7 +703,8 @@ impl<'a> Builder<'a> {
                 llvm::Lld,
                 llvm::CrtBeginEnd,
                 tool::RustdocGUITest,
-                tool::OptimizedDist
+                tool::OptimizedDist,
+                tool::CoverageDump,
             ),
             Kind::Check | Kind::Clippy | Kind::Fix => describe!(
                 check::Std,
@@ -725,6 +726,7 @@ impl<'a> Builder<'a> {
                 test::Tidy,
                 test::Ui,
                 test::RunPassValgrind,
+                test::CoverageMap,
                 test::RunCoverage,
                 test::MirOpt,
                 test::Codegen,
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index d1018978f78..d78e0deda69 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1340,6 +1340,12 @@ host_test!(RunMakeFullDeps {
 
 default_test!(Assembly { path: "tests/assembly", mode: "assembly", suite: "assembly" });
 
+default_test!(CoverageMap {
+    path: "tests/coverage-map",
+    mode: "coverage-map",
+    suite: "coverage-map"
+});
+
 host_test!(RunCoverage { path: "tests/run-coverage", mode: "run-coverage", suite: "run-coverage" });
 host_test!(RunCoverageRustdoc {
     path: "tests/run-coverage-rustdoc",
@@ -1545,6 +1551,14 @@ note: if you're sure you want to do this, please open an issue as to why. In the
                 .arg(builder.ensure(tool::JsonDocLint { compiler: json_compiler, target }));
         }
 
+        if mode == "coverage-map" {
+            let coverage_dump = builder.ensure(tool::CoverageDump {
+                compiler: compiler.with_stage(0),
+                target: compiler.host,
+            });
+            cmd.arg("--coverage-dump-path").arg(coverage_dump);
+        }
+
         if mode == "run-make" || mode == "run-coverage" {
             let rust_demangler = builder
                 .ensure(tool::RustDemangler {
diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 07ff3da6b4a..f094dd9d7c9 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -306,6 +306,7 @@ bootstrap_tool!(
     GenerateWindowsSys, "src/tools/generate-windows-sys", "generate-windows-sys";
     RustdocGUITest, "src/tools/rustdoc-gui-test", "rustdoc-gui-test", is_unstable_tool = true, allow_features = "test";
     OptimizedDist, "src/tools/opt-dist", "opt-dist";
+    CoverageDump, "src/tools/coverage-dump", "coverage-dump";
 );
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, Ord, PartialOrd)]