Update CoverageMappingFormat Support to Version6

Version 5 adds Branch Regions which are a prerequisite for branch coverage.
Version 6 can use the zeroth filename as prefix for other relative files.

2 files changed, 50 insertions, 12 deletions

diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
index 6830864ba04..67cd5363a7b 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
@@ -17,10 +17,10 @@ use tracing::debug;
 
 /// Generates and exports the Coverage Map.
 ///
-/// This Coverage Map complies with Coverage Mapping Format version 4 (zero-based encoded as 3),
-/// as defined at [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/11.0-2020-10-12/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format)
-/// and published in Rust's November 2020 fork of LLVM. This version is supported by the LLVM
-/// coverage tools (`llvm-profdata` and `llvm-cov`) bundled with Rust's fork of LLVM.
+/// This Coverage Map complies with Coverage Mapping Format version 5 (zero-based encoded as 4),
+/// as defined at [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/13.0-2021-09-30/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format).
+/// This version is supported by the LLVM coverage tools (`llvm-profdata` and `llvm-cov`)
+/// bundled with Rust's fork of LLVM.
 ///
 /// Consequently, Rust's bundled version of Clang also generates Coverage Maps compliant with
 /// the same version. Clang's implementation of Coverage Map generation was referenced when
@@ -30,12 +30,12 @@ use tracing::debug;
 pub fn finalize<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
     let tcx = cx.tcx;
 
-    // Ensure LLVM supports Coverage Map Version 4 (encoded as a zero-based value: 3).
-    // If not, the LLVM Version must be less than 11.
-    let version = coverageinfo::mapping_version();
-    if version != 3 {
-        tcx.sess.fatal("rustc option `-Z instrument-coverage` requires LLVM 11 or higher.");
-    }
+    // While our bundled LLVM might support Coverage Map Version 6
+    // (encoded as a zero-based value: 5), we clamp that to Version 5,
+    // as Version 6 would require us to use the 0-th filename as a path prefix
+    // for all other relative paths, which we don't take advantage of right now.
+    let _version = coverageinfo::mapping_version();
+    let version = 4;
 
     debug!("Generating coverage map for CodegenUnit: `{}`", cx.codegen_unit.name());
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 1d255c07559..badb386b6b1 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -681,7 +681,7 @@ pub type InlineAsmDiagHandler = unsafe extern "C" fn(&SMDiagnostic, *const c_voi
 pub mod coverageinfo {
     use super::coverage_map;
 
-    /// Aligns with [llvm::coverage::CounterMappingRegion::RegionKind](https://github.com/rust-lang/llvm-project/blob/rustc/11.0-2020-10-12/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L206-L222)
+    /// Aligns with [llvm::coverage::CounterMappingRegion::RegionKind](https://github.com/rust-lang/llvm-project/blob/rustc/13.0-2021-09-30/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L209-L230)
     #[derive(Copy, Clone, Debug)]
     #[repr(C)]
     pub enum RegionKind {
@@ -700,11 +700,16 @@ pub mod coverageinfo {
         /// A GapRegion is like a CodeRegion, but its count is only set as the
         /// line execution count when its the only region in the line.
         GapRegion = 3,
+
+        /// A BranchRegion represents leaf-level boolean expressions and is
+        /// associated with two counters, each representing the number of times the
+        /// expression evaluates to true or false.
+        BranchRegion = 4,
     }
 
     /// This struct provides LLVM's representation of a "CoverageMappingRegion", encoded into the
     /// coverage map, in accordance with the
-    /// [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/11.0-2020-10-12/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format).
+    /// [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/13.0-2021-09-30/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format).
     /// The struct composes fields representing the `Counter` type and value(s) (injected counter
     /// ID, or expression type and operands), the source file (an indirect index into a "filenames
     /// array", encoded separately), and source location (start and end positions of the represented
@@ -717,6 +722,10 @@ pub mod coverageinfo {
         /// The counter type and type-dependent counter data, if any.
         counter: coverage_map::Counter,
 
+        /// If the `RegionKind` is a `BranchRegion`, this represents the counter
+        /// for the false branch of the region.
+        false_counter: coverage_map::Counter,
+
         /// An indirect reference to the source filename. In the LLVM Coverage Mapping Format, the
         /// file_id is an index into a function-specific `virtual_file_mapping` array of indexes
         /// that, in turn, are used to look up the filename for this region.
@@ -754,6 +763,7 @@ pub mod coverageinfo {
         ) -> Self {
             Self {
                 counter,
+                false_counter: coverage_map::Counter::zero(),
                 file_id,
                 expanded_file_id: 0,
                 start_line,
@@ -767,6 +777,31 @@ pub mod coverageinfo {
         // This function might be used in the future; the LLVM API is still evolving, as is coverage
         // support.
         #[allow(dead_code)]
+        crate fn branch_region(
+            counter: coverage_map::Counter,
+            false_counter: coverage_map::Counter,
+            file_id: u32,
+            start_line: u32,
+            start_col: u32,
+            end_line: u32,
+            end_col: u32,
+        ) -> Self {
+            Self {
+                counter,
+                false_counter,
+                file_id,
+                expanded_file_id: 0,
+                start_line,
+                start_col,
+                end_line,
+                end_col,
+                kind: RegionKind::BranchRegion,
+            }
+        }
+
+        // This function might be used in the future; the LLVM API is still evolving, as is coverage
+        // support.
+        #[allow(dead_code)]
         crate fn expansion_region(
             file_id: u32,
             expanded_file_id: u32,
@@ -777,6 +812,7 @@ pub mod coverageinfo {
         ) -> Self {
             Self {
                 counter: coverage_map::Counter::zero(),
+                false_counter: coverage_map::Counter::zero(),
                 file_id,
                 expanded_file_id,
                 start_line,
@@ -799,6 +835,7 @@ pub mod coverageinfo {
         ) -> Self {
             Self {
                 counter: coverage_map::Counter::zero(),
+                false_counter: coverage_map::Counter::zero(),
                 file_id,
                 expanded_file_id: 0,
                 start_line,
@@ -822,6 +859,7 @@ pub mod coverageinfo {
         ) -> Self {
             Self {
                 counter,
+                false_counter: coverage_map::Counter::zero(),
                 file_id,
                 expanded_file_id: 0,
                 start_line,