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

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

Tracking issue: #42524

MCP: https://github.com/rust-lang/compiler-team/issues/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,