Add hotness data to LLVM remarks

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -320,6 +320,7 @@ impl<'a> DiagnosticHandlers<'a> {
             })
             .and_then(|dir| dir.to_str().and_then(|p| CString::new(p).ok()));
 
+        let pgo_available = cgcx.opts.cg.profile_use.is_some();
         let data = Box::into_raw(Box::new((cgcx, handler)));
         unsafe {
             let old_handler = llvm::LLVMRustContextGetDiagnosticHandler(llcx);
@@ -333,6 +334,7 @@ impl<'a> DiagnosticHandlers<'a> {
                 // The `as_ref()` is important here, otherwise the `CString` will be dropped
                 // too soon!
                 remark_file.as_ref().map(|dir| dir.as_ptr()).unwrap_or(std::ptr::null()),
+                pgo_available,
             );
             DiagnosticHandlers { data, llcx, old_handler }
         }

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2332,6 +2332,7 @@ extern "C" {
         remark_passes: *const *const c_char,
         remark_passes_len: usize,
         remark_file: *const c_char,
+        pgo_available: bool,
     );
 
     #[allow(improper_ctypes)]

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -1869,7 +1869,8 @@ extern "C" void LLVMRustContextConfigureDiagnosticHandler(
     LLVMContextRef C, LLVMDiagnosticHandlerTy DiagnosticHandlerCallback,
     void *DiagnosticHandlerContext, bool RemarkAllPasses,
     const char * const * RemarkPasses, size_t RemarkPassesLen,
-    const char * RemarkFilePath
+    const char * RemarkFilePath,
+    bool PGOAvailable
 ) {
 
   class RustDiagnosticHandler final : public DiagnosticHandler {
@@ -1967,6 +1968,11 @@ extern "C" void LLVMRustContextConfigureDiagnosticHandler(
   std::unique_ptr<LLVMRemarkStreamer> LlvmRemarkStreamer;
 
   if (RemarkFilePath != nullptr) {
+    if (PGOAvailable) {
+      // Enable PGO hotness data for remarks, if available
+      unwrap(C)->setDiagnosticsHotnessRequested(true);
+    }
+
     std::error_code EC;
     RemarkFile = std::make_unique<ToolOutputFile>(
       RemarkFilePath,

tests/run-make/optimization-remarks-dir-pgo/Makefile

@@ -0,0 +1,20 @@
+# needs-profiler-support
+# ignore-windows-gnu
+
+# FIXME(mati865): MinGW GCC miscompiles compiler-rt profiling library but with Clang it works
+# properly. Since we only have GCC on the CI ignore the test for now.
+
+include ../tools.mk
+
+PROFILE_DIR=$(TMPDIR)/profiles
+
+check_hotness:
+	$(RUSTC) -Cprofile-generate="$(TMPDIR)"/profdata -O foo.rs -o$(TMPDIR)/foo
+	$(TMPDIR)/foo
+	"$(LLVM_BIN_DIR)"/llvm-profdata merge \
+		-o "$(TMPDIR)"/merged.profdata \
+		"$(TMPDIR)"/profdata/*.profraw
+	$(RUSTC) -Cprofile-use=$(TMPDIR)/merged.profdata -O foo.rs -Cremark=all -Zremark-dir=$(PROFILE_DIR)
+
+	# Check that PGO hotness is included in the remark files
+	cat $(PROFILE_DIR)/*.opt.yaml | $(CGREP) -e "Hotness"

tests/run-make/optimization-remarks-dir-pgo/foo.rs

@@ -0,0 +1,6 @@
+#[inline(never)]
+pub fn bar() {}
+
+fn main() {
+    bar();
+}