Rollup merge of rust-lang#106625 - Swatinem:ref/cov6, r=nagisa

Remove backwards compat for LLVM 12 coverage format

The minimum external LLVM was updated to 13 recently in rust-lang#100611, so this PR removes backwards compat with older coverage formats.

I kept the version check and error message there, in accordance with this comment: rust-lang#91207 (comment)

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -1,6 +1,5 @@
 use crate::common::CodegenCx;
 use crate::coverageinfo;
-use crate::errors::InstrumentCoverageRequiresLLVM12;
 use crate::llvm;
 
 use llvm::coverageinfo::CounterMappingRegion;
@@ -19,8 +18,8 @@ use std::ffi::CString;
 
 /// Generates and exports the Coverage Map.
 ///
-/// Rust Coverage Map generation supports LLVM Coverage Mapping Format versions
-/// 5 (LLVM 12, only) and 6 (zero-based encoded as 4 and 5, respectively), as defined at
+/// Rust Coverage Map generation supports LLVM Coverage Mapping Format version
+/// 6 (zero-based encoded as 5), 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).
 /// These versions are supported by the LLVM coverage tools (`llvm-profdata` and `llvm-cov`)
 /// bundled with Rust's fork of LLVM.
@@ -33,13 +32,10 @@ use std::ffi::CString;
 pub fn finalize(cx: &CodegenCx<'_, '_>) {
     let tcx = cx.tcx;
 
-    // Ensure the installed version of LLVM supports at least Coverage Map
-    // Version 5 (encoded as a zero-based value: 4), which was introduced with
-    // LLVM 12.
+    // Ensure the installed version of LLVM supports Coverage Map Version 6
+    // (encoded as a zero-based value: 5), which was introduced with LLVM 13.
     let version = coverageinfo::mapping_version();
-    if version < 4 {
-        tcx.sess.emit_fatal(InstrumentCoverageRequiresLLVM12);
-    }
+    assert_eq!(version, 5, "The `CoverageMappingVersion` exposed by `llvm-wrapper` is out of sync");
 
     debug!("Generating coverage map for CodegenUnit: `{}`", cx.codegen_unit.name());
 
@@ -61,7 +57,7 @@ pub fn finalize(cx: &CodegenCx<'_, '_>) {
         return;
     }
 
-    let mut mapgen = CoverageMapGenerator::new(tcx, version);
+    let mut mapgen = CoverageMapGenerator::new(tcx);
 
     // Encode coverage mappings and generate function records
     let mut function_data = Vec::new();
@@ -124,25 +120,18 @@ struct CoverageMapGenerator {
 }
 
 impl CoverageMapGenerator {
-    fn new(tcx: TyCtxt<'_>, version: u32) -> Self {
+    fn new(tcx: TyCtxt<'_>) -> Self {
         let mut filenames = FxIndexSet::default();
-        if version >= 5 {
-            // LLVM Coverage Mapping Format version 6 (zero-based encoded as 5)
-            // requires setting the first filename to the compilation directory.
-            // Since rustc generates coverage maps with relative paths, the
-            // compilation directory can be combined with the relative paths
-            // to get absolute paths, if needed.
-            let working_dir = tcx
-                .sess
-                .opts
-                .working_dir
-                .remapped_path_if_available()
-                .to_string_lossy()
-                .to_string();
-            let c_filename =
-                CString::new(working_dir).expect("null error converting filename to C string");
-            filenames.insert(c_filename);
-        }
+        // LLVM Coverage Mapping Format version 6 (zero-based encoded as 5)
+        // requires setting the first filename to the compilation directory.
+        // Since rustc generates coverage maps with relative paths, the
+        // compilation directory can be combined with the relative paths
+        // to get absolute paths, if needed.
+        let working_dir =
+            tcx.sess.opts.working_dir.remapped_path_if_available().to_string_lossy().to_string();
+        let c_filename =
+            CString::new(working_dir).expect("null error converting filename to C string");
+        filenames.insert(c_filename);
         Self { filenames }
     }
 

compiler/rustc_codegen_llvm/src/errors.rs

@@ -39,10 +39,6 @@ pub(crate) struct ErrorCreatingImportLibrary<'a> {
     pub error: String,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_llvm_instrument_coverage_requires_llvm_12)]
-pub(crate) struct InstrumentCoverageRequiresLLVM12;
-
 #[derive(Diagnostic)]
 #[diag(codegen_llvm_symbol_already_defined)]
 pub(crate) struct SymbolAlreadyDefined<'a> {

compiler/rustc_error_messages/locales/en-US/codegen_llvm.ftl

@@ -11,9 +11,6 @@ codegen_llvm_unknown_ctarget_feature_prefix =
 codegen_llvm_error_creating_import_library =
     Error creating import library for {$lib_name}: {$error}
 
-codegen_llvm_instrument_coverage_requires_llvm_12 =
-    rustc option `-C instrument-coverage` requires LLVM 12 or higher.
-
 codegen_llvm_symbol_already_defined =
     symbol `{$symbol_name}` is already defined