Skip to content

Commit

Permalink
coverage: Emit mappings for unused functions without generating stubs
Browse files Browse the repository at this point in the history
  • Loading branch information
@Zalathar
Zalathar committed Oct 19, 2023
1 parent 36b61e5 commit b8688f9
Show file tree
Hide file tree
Showing 2 changed files with 37 additions and 74 deletions.
35 changes: 30 additions & 5 deletions compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use crate::coverageinfo::ffi::CounterMappingRegion;
use crate::coverageinfo::map_data::FunctionCoverage;
use crate::llvm;

use rustc_codegen_ssa::traits::ConstMethods;
use rustc_codegen_ssa::traits::{BaseTypeMethods, ConstMethods};
use rustc_data_structures::fx::FxIndexSet;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
Expand Down Expand Up @@ -94,8 +94,14 @@ pub fn finalize(cx: &CodegenCx<'_, '_>) {
// Generate the LLVM IR representation of the coverage map and store it in a well-known global
let cov_data_val = generate_coverage_map(cx, version, filenames_size, filenames_val);

let mut unused_function_names = Vec::new();

let covfun_section_name = coverageinfo::covfun_section_name(cx);
for (mangled_function_name, source_hash, is_used, coverage_mapping_buffer) in function_data {
if !is_used {
unused_function_names.push(mangled_function_name);
}

save_function_record(
cx,
&covfun_section_name,
Expand All @@ -107,6 +113,25 @@ pub fn finalize(cx: &CodegenCx<'_, '_>) {
);
}

// For unused functions, we need to take their mangled names and store them
// in a specially-named global array. LLVM's `InstrProfiling` pass will
// detect this global and include those names in its `__llvm_prf_names`
// section. (See `llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp`.)
if !unused_function_names.is_empty() {
assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());

let name_globals = unused_function_names
.into_iter()
.map(|mangled_function_name| cx.const_str(mangled_function_name).0)
.collect::<Vec<_>>();
let initializer = cx.const_array(cx.type_ptr(), &name_globals);

let array = llvm::add_global(cx.llmod, cx.val_ty(initializer), "__llvm_coverage_names");
llvm::set_global_constant(array, true);
llvm::set_linkage(array, llvm::Linkage::InternalLinkage);
llvm::set_initializer(array, initializer);
}

// Save the coverage data value to LLVM IR
coverageinfo::save_cov_data_to_mod(cx, cov_data_val);
}
Expand Down Expand Up @@ -290,10 +315,10 @@ fn save_function_record(
/// `DefId`s (`tcx` query `mir_keys`) minus the codegenned `DefId`s (`tcx` query
/// `codegened_and_inlined_items`).
///
/// These unused functions are then codegen'd in one of the CGUs which is marked as the
/// "code coverage dead code cgu" during the partitioning process. This prevents us from generating
/// code regions for the same function more than once which can lead to linker errors regarding
/// duplicate symbols.
/// These unused functions don't need to be codegenned, but we do need to add them to the function
/// coverage map (in a single designated CGU) so that we still emit coverage mappings for them.
/// We also end up adding their symbol names to a special global array that LLVM will include in
/// its embedded coverage data.
fn add_unused_functions(cx: &CodegenCx<'_, '_>) {
assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());

Expand Down
76 changes: 7 additions & 69 deletions compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
use crate::llvm;

use crate::abi::Abi;
use crate::builder::Builder;
use crate::common::CodegenCx;
use crate::coverageinfo::ffi::{CounterExpression, CounterMappingRegion};
Expand All @@ -12,26 +11,20 @@ use rustc_codegen_ssa::traits::{
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::{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 rustc_middle::ty::layout::HasTyCtxt;
use rustc_middle::ty::{self, GenericArgs, Instance, TyCtxt};

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.
Expand Down Expand Up @@ -77,22 +70,8 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
}
}

/// 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);
let instance = declare_unused_fn(self.tcx, def_id);
add_unused_function_coverage(self, instance, function_coverage_info);
}
}
Expand Down Expand Up @@ -159,10 +138,8 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
}
}

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

let instance = Instance::new(
fn declare_unused_fn<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Instance<'tcx> {
Instance::new(
def_id,
GenericArgs::for_item(tcx, def_id, |param, _| {
if let ty::GenericParamDefKind::Lifetime = param.kind {
Expand All @@ -171,46 +148,7 @@ fn declare_unused_fn<'tcx>(cx: &CodegenCx<'_, 'tcx>, def_id: DefId) -> Instance<
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>(
Expand Down

0 comments on commit b8688f9

Please sign in to comment.