Add support for generating unique profraw files by default when using -C instrument-coverage

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -423,6 +423,14 @@ fn get_pgo_sample_use_path(config: &ModuleConfig) -> Option<CString> {
         .map(|path_buf| CString::new(path_buf.to_string_lossy().as_bytes()).unwrap())
 }
 
+fn get_instr_profile_output_path(config: &ModuleConfig) -> Option<CString> {
+    if config.instrument_coverage {
+        Some(CString::new("default_%m_%p.profraw").unwrap())
+    } else {
+        None
+    }
+}
+
 pub(crate) unsafe fn optimize_with_new_llvm_pass_manager(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     diag_handler: &Handler,
@@ -438,6 +446,7 @@ pub(crate) unsafe fn optimize_with_new_llvm_pass_manager(
     let pgo_use_path = get_pgo_use_path(config);
     let pgo_sample_use_path = get_pgo_sample_use_path(config);
     let is_lto = opt_stage == llvm::OptStage::ThinLTO || opt_stage == llvm::OptStage::FatLTO;
+    let instr_profile_output_path = get_instr_profile_output_path(config);
     // Sanitizer instrumentation is only inserted during the pre-link optimization stage.
     let sanitizer_options = if !is_lto {
         Some(llvm::SanitizerOptions {
@@ -488,6 +497,7 @@ pub(crate) unsafe fn optimize_with_new_llvm_pass_manager(
         pgo_gen_path.as_ref().map_or(std::ptr::null(), |s| s.as_ptr()),
         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,

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2347,6 +2347,7 @@ extern "C" {
         PGOGenPath: *const c_char,
         PGOUsePath: *const c_char,
         InstrumentCoverage: bool,
+        InstrProfileOutput: *const c_char,
         InstrumentGCOV: bool,
         PGOSampleUsePath: *const c_char,
         DebugInfoForProfiling: bool,

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -822,7 +822,8 @@ LLVMRustOptimizeWithNewPassManager(
     bool DisableSimplifyLibCalls, bool EmitLifetimeMarkers,
     LLVMRustSanitizerOptions *SanitizerOptions,
     const char *PGOGenPath, const char *PGOUsePath,
-    bool InstrumentCoverage, bool InstrumentGCOV,
+    bool InstrumentCoverage, const char *InstrProfileOutput,
+    bool InstrumentGCOV,
     const char *PGOSampleUsePath, bool DebugInfoForProfiling,
     void* LlvmSelfProfiler,
     LLVMRustSelfProfileBeforePassCallback BeforePassCallback,
@@ -922,8 +923,11 @@ LLVMRustOptimizeWithNewPassManager(
 
   if (InstrumentCoverage) {
     PipelineStartEPCallbacks.push_back(
-      [](ModulePassManager &MPM, OptimizationLevel Level) {
+      [InstrProfileOutput](ModulePassManager &MPM, OptimizationLevel Level) {
         InstrProfOptions Options;
+        if (InstrProfileOutput) {
+          Options.InstrProfileOutput = InstrProfileOutput;
+        }
         MPM.addPass(InstrProfiling(Options, false));
       }
     );

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

@@ -97,7 +97,17 @@ $ echo "{some: 'thing'}" | target/debug/examples/formatjson5 -
 }
 ```
 
-After running this program, a new file, `default.profraw`, should be in the current working directory. It's often preferable to set a specific file name or path. You can change the output file using the environment variable `LLVM_PROFILE_FILE`:
+After running this program, a new file named like `default_11699812450447639123_0_20944` should be in the current working directory.
+A new, unique file name will be generated each time the program is run to avoid overwriting previous data.
+
+```shell
+$ echo "{some: 'thing'}" | target/debug/examples/formatjson5 -
+...
+$ ls default_*.profraw
+default_11699812450447639123_0_20944.profraw
+```
+
+You can also set a specific file name or path for the generated `.profraw` files by using the environment variable `LLVM_PROFILE_FILE`:
 
 ```shell
 $ echo "{some: 'thing'}" \
@@ -115,6 +125,9 @@ If `LLVM_PROFILE_FILE` contains a path to a non-existent directory, the missing
 -   `%Nm` - the instrumented binary’s signature: The runtime creates a pool of N raw profiles, used for on-line profile merging. The runtime takes care of selecting a raw profile from the pool, locking it, and updating it before the program exits. `N` must be between `1` and `9`, and defaults to `1` if omitted (with simply `%m`).
 -   `%c` - Does not add anything to the filename, but enables a mode (on some platforms, including Darwin) in which profile counter updates are continuously synced to a file. This means that if the instrumented program crashes, or is killed by a signal, perfect coverage information can still be recovered.
 
+In the first example above, the value `11699812450447639123_0` in the generated filename is the instrumented binary's signature,
+which replaced the `%m` pattern and the value `20944` is the process ID of the binary being executed.
+
 ## Installing LLVM coverage tools
 
 LLVM's supplies two tools—`llvm-profdata` and `llvm-cov`—that process coverage data and generate reports. There are several ways to find and/or install these tools, but note that the coverage mapping data generated by the Rust compiler requires LLVM version 12 or higher, and processing the *raw* data may require exactly the LLVM version used by the compiler. (`llvm-cov --version` typically shows the tool's LLVM version number, and `rustc --verbose --version` shows the version of LLVM used by the Rust compiler.)
@@ -181,11 +194,10 @@ A typical use case for coverage analysis is test coverage. Rust's source-based c
 
 The following example (using the [`json5format`] crate, for demonstration purposes) show how to generate and analyze coverage results for all tests in a crate.
 
-Since `cargo test` both builds and runs the tests, we set both the additional `RUSTFLAGS`, to add the `-C instrument-coverage` flag, and `LLVM_PROFILE_FILE`, to set a custom filename for the raw profiling data generated during the test runs. Since there may be more than one test binary, apply `%m` in the filename pattern. This generates unique names for each test binary. (Otherwise, each executed test binary would overwrite the coverage results from the previous binary.)
+Since `cargo test` both builds and runs the tests, we set the additional `RUSTFLAGS`, to add the `-C instrument-coverage` flag.
 
 ```shell
 $ RUSTFLAGS="-C instrument-coverage" \
-    LLVM_PROFILE_FILE="json5format-%m.profraw" \
     cargo test --tests
 ```
 
@@ -210,7 +222,7 @@ test result: ok. 31 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
 You should have one or more `.profraw` files now, one for each test binary. Run the `profdata` tool to merge them:
 
 ```shell
-$ llvm-profdata merge -sparse json5format-*.profraw -o json5format.profdata
+$ llvm-profdata merge -sparse default_*.profraw -o json5format.profdata
 ```
 
 Then run the `cov` tool, with the `profdata` file and all test binaries:
@@ -230,6 +242,8 @@ $ llvm-cov show \
     --Xdemangler=rustfilt | less -R
 ```
 
+> **Note**: If overriding the default `profraw` file name via the `LLVM_PROFILE_FILE` environment variable, it's highly recommended to use the `%m` and `%p` special pattern strings to generate unique file names in the case of more than a single test binary being executed.
+
 > **Note**: The command line option `--ignore-filename-regex=/.cargo/registry`, which excludes the sources for dependencies from the coverage results.\_
 
 ### Tips for listing the binaries automatically
@@ -271,9 +285,8 @@ To include doc tests in the coverage results, drop the `--tests` flag, and apply
 ```bash
 $ RUSTFLAGS="-C instrument-coverage" \
   RUSTDOCFLAGS="-C instrument-coverage -Z unstable-options --persist-doctests target/debug/doctestbins" \
-  LLVM_PROFILE_FILE="json5format-%m.profraw" \
     cargo test
-$ llvm-profdata merge -sparse json5format-*.profraw -o json5format.profdata
+$ llvm-profdata merge -sparse default_*.profraw -o json5format.profdata
 ```
 
 The `-Z unstable-options --persist-doctests` flag is required, to save the test binaries
@@ -302,8 +315,7 @@ $ llvm-cov report \
 > version without doc tests, include:
 
 -   The `cargo test ... --no-run` command is updated with the same environment variables
-    and flags used to _build_ the tests, _including_ the doc tests. (`LLVM_PROFILE_FILE`
-    is only used when _running_ the tests.)
+    and flags used to _build_ the tests, _including_ the doc tests.
 -   The file glob pattern `target/debug/doctestbins/*/rust_out` adds the `rust_out`
     binaries generated for doc tests (note, however, that some `rust_out` files may not
     be executable binaries).

src/test/codegen/instrument-coverage.rs

@@ -0,0 +1,17 @@
+// Test that `-Cinstrument-coverage` creates expected __llvm_profile_filename symbol in LLVM IR.
+
+// needs-profiler-support
+// compile-flags: -Cinstrument-coverage
+
+// CHECK: @__llvm_profile_filename = {{.*}}"default_%m_%p.profraw\00"{{.*}}
+
+#![crate_type="lib"]
+
+#[inline(never)]
+fn some_function() {
+
+}
+
+pub fn some_other_function() {
+    some_function();
+}