coverage: Store covfun_section_name in the codegen context

Adding an extra `OnceCell` to `CrateCoverageContext` is much nicer than trying to thread this string through multiple layers of function calls that already have access to the context.

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -1,4 +1,4 @@
-use std::ffi::{CStr, CString};
+use std::ffi::CString;
 
 use itertools::Itertools as _;
 use rustc_abi::Align;
@@ -81,7 +81,6 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
  generate_covmap_record(cx, covmap_version, filenames_size, filenames_val);
 
  let mut unused_function_names = Vec::new();
- let covfun_section_name = coverageinfo::covfun_section_name(cx);
 
  // Encode coverage mappings and generate function records
  for (instance, function_coverage) in function_coverage_entries {
@@ -112,7 +111,6 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
 
  generate_covfun_record(
  cx,
- &covfun_section_name,
  mangled_function_name,
  source_hash,
  filenames_ref,
@@ -360,7 +358,6 @@ fn generate_covmap_record<'ll>(
 /// as a global variable in the `__llvm_covfun` section.
 fn generate_covfun_record(
  cx: &CodegenCx<'_, '_>,
- covfun_section_name: &CStr,
  mangled_function_name: &str,
  source_hash: u64,
  filenames_ref: u64,
@@ -401,7 +398,7 @@ fn generate_covfun_record(
  llvm::set_global_constant(llglobal, true);
  llvm::set_linkage(llglobal, llvm::Linkage::LinkOnceODRLinkage);
  llvm::set_visibility(llglobal, llvm::Visibility::Hidden);
- llvm::set_section(llglobal, covfun_section_name);
+ llvm::set_section(llglobal, cx.covfun_section_name());
  // LLVM's coverage mapping format specifies 8-byte alignment for items in this section.
  llvm::set_alignment(llglobal, Align::EIGHT);
  if cx.target_spec().supports_comdat() {

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -1,5 +1,5 @@
-use std::cell::RefCell;
-use std::ffi::CString;
+use std::cell::{OnceCell, RefCell};
+use std::ffi::{CStr, CString};
 
 use libc::c_uint;
 use rustc_codegen_ssa::traits::{
@@ -29,6 +29,8 @@ pub(crate) struct CrateCoverageContext<'ll, 'tcx> {
  RefCell<FxIndexMap<Instance<'tcx>, FunctionCoverageCollector<'tcx>>>,
  pub(crate) pgo_func_name_var_map: RefCell<FxHashMap<Instance<'tcx>, &'ll llvm::Value>>,
  pub(crate) mcdc_condition_bitmap_map: RefCell<FxHashMap<Instance<'tcx>, Vec<&'ll llvm::Value>>>,
+
+ covfun_section_name: OnceCell<CString>,
 }
 
 impl<'ll, 'tcx> CrateCoverageContext<'ll, 'tcx> {
@@ -37,6 +39,7 @@ impl<'ll, 'tcx> CrateCoverageContext<'ll, 'tcx> {
  function_coverage_map: Default::default(),
  pgo_func_name_var_map: Default::default(),
  mcdc_condition_bitmap_map: Default::default(),
+ covfun_section_name: Default::default(),
  }
  }
 
@@ -63,13 +66,28 @@ impl<'ll, 'tcx> CrateCoverageContext<'ll, 'tcx> {
  }
 }
 
-// These methods used to be part of trait `CoverageInfoMethods`, which no longer
-// exists after most coverage code was moved out of SSA.
 impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
  pub(crate) fn coverageinfo_finalize(&self) {
  mapgen::finalize(self)
  }
 
+ /// Returns the section name to use when embedding per-function coverage information
+ /// in the object file, according to the target's object file format. LLVM's coverage
+ /// tools use information from this section when producing coverage reports.
+ ///
+ /// Typical values are:
+ /// - `__llvm_covfun` on Linux
+ /// - `__LLVM_COV,__llvm_covfun` on macOS (includes `__LLVM_COV,` segment prefix)
+ /// - `.lcovfun$M` on Windows (includes `$M` sorting suffix)
+ fn covfun_section_name(&self) -> &CStr {
+ self.coverage_cx().covfun_section_name.get_or_init(|| {
+ CString::new(llvm::build_byte_buffer(|s| unsafe {
+ llvm::LLVMRustCoverageWriteFuncSectionNameToString(self.llmod, s);
+ }))
+ .expect("covfun section name should not contain NUL")
+ })
+ }
+
  /// For LLVM codegen, returns a function-specific `Value` for a global
  /// string, to hold the function name passed to LLVM intrinsic
  /// `instrprof.increment()`. The `Value` is only created once per instance.
@@ -278,21 +296,3 @@ pub(crate) fn hash_bytes(bytes: &[u8]) -> u64 {
 pub(crate) fn mapping_version() -> u32 {
  unsafe { llvm::LLVMRustCoverageMappingVersion() }
 }
-
-/// Returns the section name string to pass through to the linker when embedding
-/// per-function coverage information in the object file, according to the target
-/// platform's object file format.
-///
-/// LLVM's coverage tools read coverage mapping details from this section when
-/// producing coverage reports.
-///
-/// Typical values are:
-/// - `__llvm_covfun` on Linux
-/// - `__LLVM_COV,__llvm_covfun` on macOS (includes `__LLVM_COV,` segment prefix)
-/// - `.lcovfun$M` on Windows (includes `$M` sorting suffix)
-pub(crate) fn covfun_section_name(cx: &CodegenCx<'_, '_>) -> CString {
- CString::new(llvm::build_byte_buffer(|s| unsafe {
- llvm::LLVMRustCoverageWriteFuncSectionNameToString(cx.llmod, s);
- }))
- .expect("covfun section name should not contain NUL")
-}