Rollup merge of #131829 - Zalathar:goodbye-zprofile, r=chenyukang

Remove support for `-Zprofile` (gcov-style coverage instrumentation)

Tracking issue: #42524

MCP: rust-lang/compiler-team#798

---

This PR removes the unstable `-Zprofile` flag, which enables ”gcov-style” coverage instrumentation, along with its associated `-Zprofile-emit` configuration flag.

(The profile flag predates and is almost entirely separate from the stable `-Cinstrument-coverage` flag.)

Notably, the `-Zprofile` flag:
- Is largely untested in-tree, having only one run-make test that does not check whether its output is correct or useful.
- Has no known maintainer.
- Has seen no push towards stabilization.
- Has at least one severe regression reported in 2022 that apparently remains unaddressed.
  - #100125
- Is confusingly named, since it appears to be more about coverage than performance profiling, and has nothing to do with PGO.
- Is fundamentally limited by relying on counters auto-inserted by LLVM, with no knowledge of Rust beyond debuginfo.

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -232,11 +232,6 @@ fn probestack_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribute> {
         return None;
     }
 
-    // probestack doesn't play nice either with gcov profiling.
-    if cx.sess().opts.unstable_opts.profile {
-        return None;
-    }
-
     let attr_value = match cx.sess().target.stack_probes {
         StackProbeType::None => return None,
         // Request LLVM to generate the probes inline. If the given LLVM version does not support

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -591,7 +591,6 @@ pub(crate) unsafe fn llvm_optimize(
             pgo_use_path.as_ref().map_or(std::ptr::null(), |s| s.as_ptr()),
             config.instrument_coverage,
             instr_profile_output_path.as_ref().map_or(std::ptr::null(), |s| s.as_ptr()),
-            config.instrument_gcov,
             pgo_sample_use_path.as_ref().map_or(std::ptr::null(), |s| s.as_ptr()),
             config.debug_info_for_profiling,
             llvm_selfprofiler,

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -7,7 +7,6 @@ use std::{iter, ptr};
 use libc::{c_char, c_longlong, c_uint};
 use rustc_codegen_ssa::debuginfo::type_names::{VTableNameKind, cpp_like_debuginfo};
 use rustc_codegen_ssa::traits::*;
-use rustc_fs_util::path_to_c_string;
 use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::bug;
@@ -979,33 +978,8 @@ pub(crate) fn build_compile_unit_di_node<'ll, 'tcx>(
             debug_name_table_kind,
         );
 
-        if tcx.sess.opts.unstable_opts.profile {
-            let default_gcda_path = &output_filenames.with_extension("gcda");
-            let gcda_path =
-                tcx.sess.opts.unstable_opts.profile_emit.as_ref().unwrap_or(default_gcda_path);
-
-            let gcov_cu_info = [
-                path_to_mdstring(debug_context.llcontext, &output_filenames.with_extension("gcno")),
-                path_to_mdstring(debug_context.llcontext, gcda_path),
-                unit_metadata,
-            ];
-            let gcov_metadata = llvm::LLVMMDNodeInContext2(
-                debug_context.llcontext,
-                gcov_cu_info.as_ptr(),
-                gcov_cu_info.len(),
-            );
-            let val = llvm::LLVMMetadataAsValue(debug_context.llcontext, gcov_metadata);
-
-            llvm::LLVMAddNamedMetadataOperand(debug_context.llmod, c"llvm.gcov".as_ptr(), val);
-        }
-
         return unit_metadata;
     };
-
-    fn path_to_mdstring<'ll>(llcx: &'ll llvm::Context, path: &Path) -> &'ll llvm::Metadata {
-        let path_str = path_to_c_string(path);
-        unsafe { llvm::LLVMMDStringInContext2(llcx, path_str.as_ptr(), path_str.as_bytes().len()) }
-    }
 }
 
 /// Creates a `DW_TAG_member` entry inside the DIE represented by the given `type_di_node`.

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -55,7 +55,6 @@ const DW_TAG_arg_variable: c_uint = 0x101;
 
 /// A context object for maintaining all state needed by the debuginfo module.
 pub(crate) struct CodegenUnitDebugContext<'ll, 'tcx> {
-    llcontext: &'ll llvm::Context,
     llmod: &'ll llvm::Module,
     builder: &'ll mut DIBuilder<'ll>,
     created_files: RefCell<UnordMap<Option<(StableSourceFileId, SourceFileHash)>, &'ll DIFile>>,
@@ -78,9 +77,7 @@ impl<'ll, 'tcx> CodegenUnitDebugContext<'ll, 'tcx> {
         debug!("CodegenUnitDebugContext::new");
         let builder = unsafe { llvm::LLVMRustDIBuilderCreate(llmod) };
         // DIBuilder inherits context from the module, so we'd better use the same one
-        let llcontext = unsafe { llvm::LLVMGetModuleContext(llmod) };
         CodegenUnitDebugContext {
-            llcontext,
             llmod,
             builder,
             created_files: Default::default(),

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2269,7 +2269,6 @@ unsafe extern "C" {
         PGOUsePath: *const c_char,
         InstrumentCoverage: bool,
         InstrProfileOutput: *const c_char,
-        InstrumentGCOV: bool,
         PGOSampleUsePath: *const c_char,
         DebugInfoForProfiling: bool,
         llvm_selfprofiler: *mut c_void,

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -90,7 +90,6 @@ pub struct ModuleConfig {
     pub pgo_sample_use: Option<PathBuf>,
     pub debug_info_for_profiling: bool,
     pub instrument_coverage: bool,
-    pub instrument_gcov: bool,
 
     pub sanitizer: SanitizerSet,
     pub sanitizer_recover: SanitizerSet,
@@ -123,12 +122,7 @@ pub struct ModuleConfig {
 }
 
 impl ModuleConfig {
-    fn new(
-        kind: ModuleKind,
-        tcx: TyCtxt<'_>,
-        no_builtins: bool,
-        is_compiler_builtins: bool,
-    ) -> ModuleConfig {
+    fn new(kind: ModuleKind, tcx: TyCtxt<'_>, no_builtins: bool) -> ModuleConfig {
         // If it's a regular module, use `$regular`, otherwise use `$other`.
         // `$regular` and `$other` are evaluated lazily.
         macro_rules! if_regular {
@@ -189,13 +183,6 @@ impl ModuleConfig {
             pgo_sample_use: if_regular!(sess.opts.unstable_opts.profile_sample_use.clone(), None),
             debug_info_for_profiling: sess.opts.unstable_opts.debug_info_for_profiling,
             instrument_coverage: if_regular!(sess.instrument_coverage(), false),
-            instrument_gcov: if_regular!(
-                // compiler_builtins overrides the codegen-units settings,
-                // which is incompatible with -Zprofile which requires that
-                // only a single codegen unit is used per crate.
-                sess.opts.unstable_opts.profile && !is_compiler_builtins,
-                false
-            ),
 
             sanitizer: if_regular!(sess.opts.unstable_opts.sanitizer, SanitizerSet::empty()),
             sanitizer_dataflow_abilist: if_regular!(
@@ -473,16 +460,12 @@ pub(crate) fn start_async_codegen<B: ExtraBackendMethods>(
 
     let crate_attrs = tcx.hir().attrs(rustc_hir::CRATE_HIR_ID);
     let no_builtins = attr::contains_name(crate_attrs, sym::no_builtins);
-    let is_compiler_builtins = attr::contains_name(crate_attrs, sym::compiler_builtins);
 
     let crate_info = CrateInfo::new(tcx, target_cpu);
 
-    let regular_config =
-        ModuleConfig::new(ModuleKind::Regular, tcx, no_builtins, is_compiler_builtins);
-    let metadata_config =
-        ModuleConfig::new(ModuleKind::Metadata, tcx, no_builtins, is_compiler_builtins);
-    let allocator_config =
-        ModuleConfig::new(ModuleKind::Allocator, tcx, no_builtins, is_compiler_builtins);
+    let regular_config = ModuleConfig::new(ModuleKind::Regular, tcx, no_builtins);
+    let metadata_config = ModuleConfig::new(ModuleKind::Metadata, tcx, no_builtins);
+    let allocator_config = ModuleConfig::new(ModuleKind::Allocator, tcx, no_builtins);
 
     let (shared_emitter, shared_emitter_main) = SharedEmitter::new();
     let (codegen_worker_send, codegen_worker_receive) = channel();

compiler/rustc_interface/src/tests.rs

@@ -832,8 +832,6 @@ fn test_unstable_options_tracking_hash() {
     tracked!(polonius, Polonius::Legacy);
     tracked!(precise_enum_drop_elaboration, false);
     tracked!(print_fuel, Some("abc".to_string()));
-    tracked!(profile, true);
-    tracked!(profile_emit, Some(PathBuf::from("abc")));
     tracked!(profile_sample_use, Some(PathBuf::from("abc")));
     tracked!(profiler_runtime, "abc".to_string());
     tracked!(regparm, Some(3));

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -42,7 +42,6 @@
 #if LLVM_VERSION_GE(19, 0)
 #include "llvm/Support/PGOOptions.h"
 #endif
-#include "llvm/Transforms/Instrumentation/GCOVProfiler.h"
 #include "llvm/Transforms/Instrumentation/HWAddressSanitizer.h"
 #include "llvm/Transforms/Instrumentation/InstrProfiling.h"
 #include "llvm/Transforms/Instrumentation/MemorySanitizer.h"
@@ -714,9 +713,8 @@ extern "C" LLVMRustResult LLVMRustOptimize(
     bool SLPVectorize, bool LoopVectorize, bool DisableSimplifyLibCalls,
     bool EmitLifetimeMarkers, LLVMRustSanitizerOptions *SanitizerOptions,
     const char *PGOGenPath, const char *PGOUsePath, bool InstrumentCoverage,
-    const char *InstrProfileOutput, bool InstrumentGCOV,
-    const char *PGOSampleUsePath, bool DebugInfoForProfiling,
-    void *LlvmSelfProfiler,
+    const char *InstrProfileOutput, const char *PGOSampleUsePath,
+    bool DebugInfoForProfiling, void *LlvmSelfProfiler,
     LLVMRustSelfProfileBeforePassCallback BeforePassCallback,
     LLVMRustSelfProfileAfterPassCallback AfterPassCallback,
     const char *ExtraPasses, size_t ExtraPassesLen, const char *LLVMPlugins,
@@ -847,13 +845,6 @@ extern "C" LLVMRustResult LLVMRustOptimize(
         });
   }
 
-  if (InstrumentGCOV) {
-    PipelineStartEPCallbacks.push_back(
-        [](ModulePassManager &MPM, OptimizationLevel Level) {
-          MPM.addPass(GCOVProfilerPass(GCOVOptions::getDefault()));
-        });
-  }
-
   if (InstrumentCoverage) {
     PipelineStartEPCallbacks.push_back(
         [InstrProfileOutput](ModulePassManager &MPM, OptimizationLevel Level) {

compiler/rustc_metadata/src/creader.rs

@@ -778,9 +778,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
 
     fn inject_profiler_runtime(&mut self, krate: &ast::Crate) {
         if self.sess.opts.unstable_opts.no_profiler_runtime
-            || !(self.sess.instrument_coverage()
-                || self.sess.opts.unstable_opts.profile
-                || self.sess.opts.cg.profile_generate.enabled())
+            || !(self.sess.instrument_coverage() || self.sess.opts.cg.profile_generate.enabled())
         {
             return;
         }

compiler/rustc_session/src/config.rs

@@ -2453,7 +2453,7 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     let output_types = parse_output_types(early_dcx, &unstable_opts, matches);
 
     let mut cg = CodegenOptions::build(early_dcx, matches);
-    let (disable_local_thinlto, mut codegen_units) = should_override_cgus_and_disable_thinlto(
+    let (disable_local_thinlto, codegen_units) = should_override_cgus_and_disable_thinlto(
         early_dcx,
         &output_types,
         matches,
@@ -2476,18 +2476,6 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
 
     let assert_incr_state = parse_assert_incr_state(early_dcx, &unstable_opts.assert_incr_state);
 
-    if unstable_opts.profile && incremental.is_some() {
-        early_dcx.early_fatal("can't instrument with gcov profiling when compiling incrementally");
-    }
-    if unstable_opts.profile {
-        match codegen_units {
-            Some(1) => {}
-            None => codegen_units = Some(1),
-            Some(_) => early_dcx
-                .early_fatal("can't instrument with gcov profiling with multiple codegen units"),
-        }
-    }
-
     if cg.profile_generate.enabled() && cg.profile_use.is_some() {
         early_dcx.early_fatal("options `-C profile-generate` and `-C profile-use` are exclusive");
     }

compiler/rustc_session/src/options.rs

@@ -1985,13 +1985,8 @@ options! {
     proc_macro_execution_strategy: ProcMacroExecutionStrategy = (ProcMacroExecutionStrategy::SameThread,
         parse_proc_macro_execution_strategy, [UNTRACKED],
         "how to run proc-macro code (default: same-thread)"),
-    profile: bool = (false, parse_bool, [TRACKED],
-        "insert profiling code (default: no)"),
     profile_closures: bool = (false, parse_no_flag, [UNTRACKED],
         "profile size of closures"),
-    profile_emit: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
-        "file path to emit profiling data at runtime when using 'profile' \
-        (default based on relative source path)"),
     profile_sample_use: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
         "use the given `.prof` file for sampled profile-guided optimization (also known as AutoFDO)"),
     profiler_runtime: String = (String::from("profiler_builtins"), parse_string, [TRACKED],

src/doc/rustc/src/instrument-coverage.md

@@ -2,12 +2,8 @@
 
 ## Introduction
 
-The Rust compiler includes two code coverage implementations:
-
--   A GCC-compatible, gcov-based coverage implementation, enabled with `-Z profile`, which derives coverage data based on DebugInfo.
--   A source-based code coverage implementation, enabled with `-C instrument-coverage`, which uses LLVM's native, efficient coverage instrumentation to generate very precise coverage data.
-
-This document describes how to enable and use the LLVM instrumentation-based coverage, via the `-C instrument-coverage` compiler flag.
+This document describes how to enable and use LLVM instrumentation-based coverage,
+via the `-C instrument-coverage` compiler flag.
 
 ## How it works