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coverage: Consolidate creation of covmap/covfun records #132124

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merged 4 commits into from
Oct 26, 2024
Merged

coverage: Consolidate creation of covmap/covfun records #132124

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9f8a6be
coverage: Consolidate creation of covmap/covfun records
Zalathar Oct 24, 2024
0a96176
coverage: Make obtaining the codegen coverage context infallible
Zalathar Oct 24, 2024
0356908
coverage: Store `covfun_section_name` in the codegen context
Zalathar Oct 24, 2024
0d653a5
coverage: Add links to LLVM docs for the coverage mapping format
Zalathar Oct 26, 2024
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83 changes: 61 additions & 22 deletions compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,7 +1,10 @@
use std::ffi::CStr;
use std::ffi::{CStr, CString};

use itertools::Itertools as _;
use rustc_codegen_ssa::traits::{BaseTypeCodegenMethods, ConstCodegenMethods};
use rustc_abi::Align;
use rustc_codegen_ssa::traits::{
BaseTypeCodegenMethods, ConstCodegenMethods, StaticCodegenMethods,
};
use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_index::IndexVec;
Expand All @@ -10,6 +13,7 @@ use rustc_middle::ty::{self, TyCtxt};
use rustc_middle::{bug, mir};
use rustc_span::Symbol;
use rustc_span::def_id::DefIdSet;
use rustc_target::spec::HasTargetSpec;
use tracing::debug;

use crate::common::CodegenCx;
Expand Down Expand Up @@ -78,8 +82,7 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {

// Generate the coverage map header, which contains the filenames used by
// this CGU's coverage mappings, and store it in a well-known global.
let cov_data_val = generate_coverage_map(cx, covmap_version, filenames_size, filenames_val);
coverageinfo::save_cov_data_to_mod(cx, cov_data_val);
generate_covmap_record(cx, covmap_version, filenames_size, filenames_val);

let mut unused_function_names = Vec::new();
let covfun_section_name = coverageinfo::covfun_section_name(cx);
Expand Down Expand Up @@ -111,7 +114,7 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
unused_function_names.push(mangled_function_name);
}

save_function_record(
generate_covfun_record(
cx,
&covfun_section_name,
mangled_function_name,
Expand Down Expand Up @@ -308,15 +311,15 @@ fn encode_mappings_for_function(
})
}

/// Construct coverage map header and the array of function records, and combine them into the
/// coverage map. Save the coverage map data into the LLVM IR as a static global using a
/// specific, well-known section and name.
fn generate_coverage_map<'ll>(
/// Generates the contents of the covmap record for this CGU, which mostly
/// consists of a header and a list of filenames. The record is then stored
/// as a global variable in the `__llvm_covmap` section.
fn generate_covmap_record<'ll>(
cx: &CodegenCx<'ll, '_>,
version: u32,
filenames_size: usize,
filenames_val: &'ll llvm::Value,
) -> &'ll llvm::Value {
) {
debug!("cov map: filenames_size = {}, 0-based version = {}", filenames_size, version);

// Create the coverage data header (Note, fields 0 and 2 are now always zero,
Expand All @@ -331,13 +334,35 @@ fn generate_coverage_map<'ll>(
);

// Create the complete LLVM coverage data value to add to the LLVM IR
cx.const_struct(&[cov_data_header_val, filenames_val], /*packed=*/ false)
let covmap_data =
cx.const_struct(&[cov_data_header_val, filenames_val], /*packed=*/ false);

let covmap_var_name = CString::new(llvm::build_byte_buffer(|s| unsafe {
llvm::LLVMRustCoverageWriteMappingVarNameToString(s);
}))
.unwrap();
debug!("covmap var name: {:?}", covmap_var_name);

let covmap_section_name = CString::new(llvm::build_byte_buffer(|s| unsafe {
llvm::LLVMRustCoverageWriteMapSectionNameToString(cx.llmod, s);
}))
.expect("covmap section name should not contain NUL");
debug!("covmap section name: {:?}", covmap_section_name);

let llglobal = llvm::add_global(cx.llmod, cx.val_ty(covmap_data), &covmap_var_name);
llvm::set_initializer(llglobal, covmap_data);
llvm::set_global_constant(llglobal, true);
llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
llvm::set_section(llglobal, &covmap_section_name);
// LLVM's coverage mapping format specifies 8-byte alignment for items in this section.
llvm::set_alignment(llglobal, Align::EIGHT);
cx.add_used_global(llglobal);
}

/// Construct a function record and combine it with the function's coverage mapping data.
/// Save the function record into the LLVM IR as a static global using a
/// specific, well-known section and name.
fn save_function_record(
/// Generates the contents of the covfun record for this function, which
/// contains the function's coverage mapping data. The record is then stored
/// as a global variable in the `__llvm_covfun` section.
fn generate_covfun_record(
cx: &CodegenCx<'_, '_>,
covfun_section_name: &CStr,
mangled_function_name: &str,
Expand Down Expand Up @@ -366,13 +391,27 @@ fn save_function_record(
/*packed=*/ true,
);

coverageinfo::save_func_record_to_mod(
cx,
covfun_section_name,
func_name_hash,
func_record_val,
is_used,
);
// Choose a variable name to hold this function's covfun data.
// Functions that are used have a suffix ("u") to distinguish them from
// unused copies of the same function (from different CGUs), so that if a
// linker sees both it won't discard the used copy's data.
let func_record_var_name =
CString::new(format!("__covrec_{:X}{}", func_name_hash, if is_used { "u" } else { "" }))
.unwrap();
debug!("function record var name: {:?}", func_record_var_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's coverage mapping format specifies 8-byte alignment for items in this section.
llvm::set_alignment(llglobal, Align::EIGHT);
if cx.target_spec().supports_comdat() {
llvm::set_comdat(cx.llmod, llglobal, &func_record_var_name);
}
cx.add_used_global(llglobal);
}

/// Each CGU will normally only emit coverage metadata for the functions that it actually generates.
Expand Down
69 changes: 3 additions & 66 deletions compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,19 +1,17 @@
use std::cell::RefCell;
use std::ffi::{CStr, CString};
use std::ffi::CString;

use libc::c_uint;
use rustc_codegen_ssa::traits::{
BaseTypeCodegenMethods, BuilderMethods, ConstCodegenMethods, CoverageInfoBuilderMethods,
MiscCodegenMethods, StaticCodegenMethods,
BuilderMethods, ConstCodegenMethods, CoverageInfoBuilderMethods, MiscCodegenMethods,
};
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_llvm::RustString;
use rustc_middle::bug;
use rustc_middle::mir::coverage::CoverageKind;
use rustc_middle::ty::Instance;
use rustc_middle::ty::layout::HasTyCtxt;
use rustc_target::abi::{Align, Size};
use rustc_target::spec::HasTargetSpec;
use rustc_target::abi::Size;
use tracing::{debug, instrument};

use crate::builder::Builder;
Expand Down Expand Up @@ -290,67 +288,6 @@ 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 = CString::new(llvm::build_byte_buffer(|s| unsafe {
llvm::LLVMRustCoverageWriteMappingVarNameToString(s);
}))
.unwrap();
debug!("covmap var name: {:?}", covmap_var_name);

let covmap_section_name = CString::new(llvm::build_byte_buffer(|s| unsafe {
llvm::LLVMRustCoverageWriteMapSectionNameToString(cx.llmod, s);
}))
.expect("covmap section name should not contain NUL");
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's coverage mapping format specifies 8-byte alignment for items in this section.
llvm::set_alignment(llglobal, Align::EIGHT);
cx.add_used_global(llglobal);
}

pub(crate) fn save_func_record_to_mod<'ll, 'tcx>(
cx: &CodegenCx<'ll, 'tcx>,
covfun_section_name: &CStr,
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 =
CString::new(format!("__covrec_{:X}{}", func_name_hash, if is_used { "u" } else { "" }))
.unwrap();
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's coverage mapping format specifies 8-byte alignment for items in this section.
llvm::set_alignment(llglobal, Align::EIGHT);
if cx.target_spec().supports_comdat() {
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.
Expand Down