rust/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

use crate::llvm;

use crate::abi::Abi;
use crate::builder::Builder;
use crate::common::CodegenCx;
use crate::coverageinfo::ffi::{CounterExpression, CounterMappingRegion};
use crate::coverageinfo::map_data::FunctionCoverage;

use libc::c_uint;
use rustc_codegen_ssa::traits::{
    BaseTypeMethods, BuilderMethods, ConstMethods, CoverageInfoBuilderMethods, MiscMethods,
    StaticMethods,
};
use rustc_data_structures::fx::FxHashMap;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_llvm::RustString;
use rustc_middle::bug;
use rustc_middle::mir::coverage::{CounterId, CoverageKind, FunctionCoverageInfo};
use rustc_middle::mir::Coverage;
use rustc_middle::ty;
use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt};
use rustc_middle::ty::GenericArgs;
use rustc_middle::ty::Instance;
use rustc_middle::ty::Ty;

use std::cell::RefCell;

pub(crate) mod ffi;
pub(crate) mod map_data;
pub mod mapgen;

const UNUSED_FUNCTION_COUNTER_ID: CounterId = CounterId::START;

const VAR_ALIGN_BYTES: usize = 8;

/// A context object for maintaining all state needed by the coverageinfo module.
pub struct CrateCoverageContext<'ll, 'tcx> {
    /// Coverage data for each instrumented function identified by DefId.
    pub(crate) function_coverage_map: RefCell<FxHashMap<Instance<'tcx>, FunctionCoverage<'tcx>>>,
    pub(crate) pgo_func_name_var_map: RefCell<FxHashMap<Instance<'tcx>, &'ll llvm::Value>>,
}

impl<'ll, 'tcx> CrateCoverageContext<'ll, 'tcx> {
    pub fn new() -> Self {
        Self {
            function_coverage_map: Default::default(),
            pgo_func_name_var_map: Default::default(),
        }
    }

    pub fn take_function_coverage_map(&self) -> FxHashMap<Instance<'tcx>, FunctionCoverage<'tcx>> {
        self.function_coverage_map.replace(FxHashMap::default())
    }
}

// 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)
    }

    /// 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.
    /// Multiple invocations with the same instance return the same `Value`.
    fn get_pgo_func_name_var(&self, instance: Instance<'tcx>) -> &'ll llvm::Value {
        if let Some(coverage_context) = self.coverage_context() {
            debug!("getting pgo_func_name_var for instance={:?}", instance);
            let mut pgo_func_name_var_map = coverage_context.pgo_func_name_var_map.borrow_mut();
            pgo_func_name_var_map
                .entry(instance)
                .or_insert_with(|| create_pgo_func_name_var(self, instance))
        } else {
            bug!("Could not get the `coverage_context`");
        }
    }

    /// Functions with MIR-based coverage are normally codegenned _only_ if
    /// called. LLVM coverage tools typically expect every function to be
    /// defined (even if unused), with at least one call to LLVM intrinsic
    /// `instrprof.increment`.
    ///
    /// Codegen a small function that will never be called, with one counter
    /// that will never be incremented.
    ///
    /// For used/called functions, the coverageinfo was already added to the
    /// `function_coverage_map` (keyed by function `Instance`) during codegen.
    /// But in this case, since the unused function was _not_ previously
    /// codegenned, collect the function coverage info from MIR and add an
    /// "unused" entry to the function coverage map.
    fn define_unused_fn(&self, def_id: DefId, function_coverage_info: &'tcx FunctionCoverageInfo) {
        let instance = declare_unused_fn(self, def_id);
        codegen_unused_fn_and_counter(self, instance);
        add_unused_function_coverage(self, instance, function_coverage_info);
    }
}

impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
    #[instrument(level = "debug", skip(self))]
    fn add_coverage(&mut self, instance: Instance<'tcx>, coverage: &Coverage) {
        let bx = self;

        let Some(function_coverage_info) =
            bx.tcx.instance_mir(instance.def).function_coverage_info.as_deref()
        else {
            debug!("function has a coverage statement but no coverage info");
            return;
        };

        let Some(coverage_context) = bx.coverage_context() else { return };
        let mut coverage_map = coverage_context.function_coverage_map.borrow_mut();
        let func_coverage = coverage_map
            .entry(instance)
            .or_insert_with(|| FunctionCoverage::new(instance, function_coverage_info));

        let Coverage { kind } = coverage;
        match *kind {
            CoverageKind::CounterIncrement { id } => {
                func_coverage.mark_counter_id_seen(id);
                // We need to explicitly drop the `RefMut` before calling into `instrprof_increment`,
                // as that needs an exclusive borrow.
                drop(coverage_map);

                // The number of counters passed to `llvm.instrprof.increment` might
                // be smaller than the number originally inserted by the instrumentor,
                // if some high-numbered counters were removed by MIR optimizations.
                // If so, LLVM's profiler runtime will use fewer physical counters.
                let num_counters =
                    bx.tcx().coverage_ids_info(instance.def).max_counter_id.as_u32() + 1;
                assert!(
                    num_counters as usize <= function_coverage_info.num_counters,
                    "num_counters disagreement: query says {num_counters} but function info only has {}",
                    function_coverage_info.num_counters
                );

                let fn_name = bx.get_pgo_func_name_var(instance);
                let hash = bx.const_u64(function_coverage_info.function_source_hash);
                let num_counters = bx.const_u32(num_counters);
                let index = bx.const_u32(id.as_u32());
                debug!(
                    "codegen intrinsic instrprof.increment(fn_name={:?}, hash={:?}, num_counters={:?}, index={:?})",
                    fn_name, hash, num_counters, index,
                );
                bx.instrprof_increment(fn_name, hash, num_counters, index);
            }
            CoverageKind::ExpressionUsed { id } => {
                func_coverage.mark_expression_id_seen(id);
            }
        }
    }
}

fn declare_unused_fn<'tcx>(cx: &CodegenCx<'_, 'tcx>, def_id: DefId) -> Instance<'tcx> {
    let tcx = cx.tcx;

    let instance = Instance::new(
        def_id,
        GenericArgs::for_item(tcx, def_id, |param, _| {
            if let ty::GenericParamDefKind::Lifetime = param.kind {
                tcx.lifetimes.re_erased.into()
            } else {
                tcx.mk_param_from_def(param)
            }
        }),
    );

    let llfn = cx.declare_fn(
        tcx.symbol_name(instance).name,
        cx.fn_abi_of_fn_ptr(
            ty::Binder::dummy(tcx.mk_fn_sig(
                [Ty::new_unit(tcx)],
                Ty::new_unit(tcx),
                false,
                hir::Unsafety::Unsafe,
                Abi::Rust,
            )),
            ty::List::empty(),
        ),
        None,
    );

    llvm::set_linkage(llfn, llvm::Linkage::PrivateLinkage);
    llvm::set_visibility(llfn, llvm::Visibility::Default);

    assert!(cx.instances.borrow_mut().insert(instance, llfn).is_none());

    instance
}

fn codegen_unused_fn_and_counter<'tcx>(cx: &CodegenCx<'_, 'tcx>, instance: Instance<'tcx>) {
    let llfn = cx.get_fn(instance);
    let llbb = Builder::append_block(cx, llfn, "unused_function");
    let mut bx = Builder::build(cx, llbb);
    let fn_name = bx.get_pgo_func_name_var(instance);
    let hash = bx.const_u64(0);
    let num_counters = bx.const_u32(1);
    let index = bx.const_u32(u32::from(UNUSED_FUNCTION_COUNTER_ID));
    debug!(
        "codegen intrinsic instrprof.increment(fn_name={:?}, hash={:?}, num_counters={:?},
            index={:?}) for unused function: {:?}",
        fn_name, hash, num_counters, index, instance
    );
    bx.instrprof_increment(fn_name, hash, num_counters, index);
    bx.ret_void();
}

fn add_unused_function_coverage<'tcx>(
    cx: &CodegenCx<'_, 'tcx>,
    instance: Instance<'tcx>,
    function_coverage_info: &'tcx FunctionCoverageInfo,
) {
    // An unused function's mappings will automatically be rewritten to map to
    // zero, because none of its counters/expressions are marked as seen.
    let function_coverage = FunctionCoverage::unused(instance, function_coverage_info);

    if let Some(coverage_context) = cx.coverage_context() {
        coverage_context.function_coverage_map.borrow_mut().insert(instance, function_coverage);
    } else {
        bug!("Could not get the `coverage_context`");
    }
}

/// Calls llvm::createPGOFuncNameVar() with the given function instance's
/// mangled function name. The LLVM API returns an llvm::GlobalVariable
/// containing the function name, with the specific variable name and linkage
/// required by LLVM InstrProf source-based coverage instrumentation. Use
/// `bx.get_pgo_func_name_var()` to ensure the variable is only created once per
/// `Instance`.
fn create_pgo_func_name_var<'ll, 'tcx>(
    cx: &CodegenCx<'ll, 'tcx>,
    instance: Instance<'tcx>,
) -> &'ll llvm::Value {
    let mangled_fn_name: &str = cx.tcx.symbol_name(instance).name;
    let llfn = cx.get_fn(instance);
    unsafe {
        llvm::LLVMRustCoverageCreatePGOFuncNameVar(
            llfn,
            mangled_fn_name.as_ptr().cast(),
            mangled_fn_name.len(),
        )
    }
}

pub(crate) fn write_filenames_section_to_buffer<'a>(
    filenames: impl IntoIterator<Item = &'a str>,
    buffer: &RustString,
) {
    let (pointers, lengths) = filenames
        .into_iter()
        .map(|s: &str| (s.as_ptr().cast(), s.len()))
        .unzip::<_, _, Vec<_>, Vec<_>>();

    unsafe {
        llvm::LLVMRustCoverageWriteFilenamesSectionToBuffer(
            pointers.as_ptr(),
            pointers.len(),
            lengths.as_ptr(),
            lengths.len(),
            buffer,
        );
    }
}

pub(crate) fn write_mapping_to_buffer(
    virtual_file_mapping: Vec<u32>,
    expressions: Vec<CounterExpression>,
    mapping_regions: Vec<CounterMappingRegion>,
    buffer: &RustString,
) {
    unsafe {
        llvm::LLVMRustCoverageWriteMappingToBuffer(
            virtual_file_mapping.as_ptr(),
            virtual_file_mapping.len() as c_uint,
            expressions.as_ptr(),
            expressions.len() as c_uint,
            mapping_regions.as_ptr(),
            mapping_regions.len() as c_uint,
            buffer,
        );
    }
}

pub(crate) fn hash_bytes(bytes: &[u8]) -> u64 {
    unsafe { llvm::LLVMRustCoverageHashByteArray(bytes.as_ptr().cast(), bytes.len()) }
}

pub(crate) fn mapping_version() -> u32 {
    unsafe { llvm::LLVMRustCoverageMappingVersion() }
}

pub(crate) fn save_cov_data_to_mod<'ll, 'tcx>(
    cx: &CodegenCx<'ll, 'tcx>,
    cov_data_val: &'ll llvm::Value,
) {
    let covmap_var_name = llvm::build_string(|s| unsafe {
        llvm::LLVMRustCoverageWriteMappingVarNameToString(s);
    })
    .expect("Rust Coverage Mapping var name failed UTF-8 conversion");
    debug!("covmap var name: {:?}", covmap_var_name);

    let covmap_section_name = llvm::build_string(|s| unsafe {
        llvm::LLVMRustCoverageWriteMapSectionNameToString(cx.llmod, s);
    })
    .expect("Rust Coverage section name failed UTF-8 conversion");
    debug!("covmap section name: {:?}", covmap_section_name);

    let llglobal = llvm::add_global(cx.llmod, cx.val_ty(cov_data_val), &covmap_var_name);
    llvm::set_initializer(llglobal, cov_data_val);
    llvm::set_global_constant(llglobal, true);
    llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
    llvm::set_section(llglobal, &covmap_section_name);
    llvm::set_alignment(llglobal, VAR_ALIGN_BYTES);
    cx.add_used_global(llglobal);
}

pub(crate) fn save_func_record_to_mod<'ll, 'tcx>(
    cx: &CodegenCx<'ll, 'tcx>,
    covfun_section_name: &str,
    func_name_hash: u64,
    func_record_val: &'ll llvm::Value,
    is_used: bool,
) {
    // Assign a name to the function record. This is used to merge duplicates.
    //
    // In LLVM, a "translation unit" (effectively, a `Crate` in Rust) can describe functions that
    // are included-but-not-used. If (or when) Rust generates functions that are
    // included-but-not-used, note that a dummy description for a function included-but-not-used
    // in a Crate can be replaced by full description provided by a different Crate. The two kinds
    // of descriptions play distinct roles in LLVM IR; therefore, assign them different names (by
    // appending "u" to the end of the function record var name, to prevent `linkonce_odr` merging.
    let func_record_var_name =
        format!("__covrec_{:X}{}", func_name_hash, if is_used { "u" } else { "" });
    debug!("function record var name: {:?}", func_record_var_name);
    debug!("function record section name: {:?}", covfun_section_name);

    let llglobal = llvm::add_global(cx.llmod, cx.val_ty(func_record_val), &func_record_var_name);
    llvm::set_initializer(llglobal, func_record_val);
    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_alignment(llglobal, VAR_ALIGN_BYTES);
    llvm::set_comdat(cx.llmod, llglobal, &func_record_var_name);
    cx.add_used_global(llglobal);
}

/// 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<'_, '_>) -> String {
    llvm::build_string(|s| unsafe {
        llvm::LLVMRustCoverageWriteFuncSectionNameToString(cx.llmod, s);
    })
    .expect("Rust Coverage function record section name failed UTF-8 conversion")
}