coverage: Emit mappings for unused functions without generating stubs

1 files changed, 7 insertions, 69 deletions

diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
index 204a73b788a..5a5f6eb89f6 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
@@ -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};
@@ -12,17 +11,13 @@ 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;
 
@@ -30,8 +25,6 @@ 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.
@@ -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);
     }
 }
@@ -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 {
@@ -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>(