don't collect #[rustc_force_inline] in eager mode

Author: davidtwco

compiler/rustc_monomorphize/src/collector.rs

@@ -225,8 +225,8 @@ use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCoercion};
 use rustc_middle::ty::layout::ValidityRequirement;
 use rustc_middle::ty::print::{shrunk_instance_name, with_no_trimmed_paths};
 use rustc_middle::ty::{
-    self, GenericArgs, GenericParamDefKind, Instance, InstanceKind, Ty, TyCtxt, TypeFoldable,
-    TypeVisitableExt, VtblEntry,
+    self, GenericArgs, GenericParamDefKind, Instance, InstanceKind, Interner, Ty, TyCtxt,
+    TypeFoldable, TypeVisitableExt, VtblEntry,
 };
 use rustc_middle::util::Providers;
 use rustc_middle::{bug, span_bug};
@@ -965,7 +965,7 @@ fn should_codegen_locally<'tcx>(tcx: TyCtxtAt<'tcx>, instance: Instance<'tcx>) -
     {
         // `#[rustc_force_inline]` items should never be codegened. This should be caught by
         // the MIR validator.
-        return false;
+        tcx.delay_bug("attempt to codegen `#[rustc_force_inline]` item");
     }
 
     if def_id.is_local() {
@@ -1462,7 +1462,9 @@ impl<'v> RootCollector<'_, 'v> {
     fn is_root(&self, def_id: LocalDefId) -> bool {
         !self.tcx.generics_of(def_id).requires_monomorphization(self.tcx)
             && match self.strategy {
-                MonoItemCollectionStrategy::Eager => true,
+                MonoItemCollectionStrategy::Eager => {
+                    !matches!(self.tcx.codegen_fn_attrs(def_id).inline, InlineAttr::Force { .. })
+                }
                 MonoItemCollectionStrategy::Lazy => {
                     self.entry_fn.and_then(|(id, _)| id.as_local()) == Some(def_id)
                         || self.tcx.is_reachable_non_generic(def_id)

tests/mir-opt/inline/forced_dead_code.caller.ForceInline.diff

@@ -0,0 +1,21 @@
+- // MIR for `caller` before ForceInline
++ // MIR for `caller` after ForceInline
+  
+  fn caller() -> () {
+      let mut _0: ();
+      let _1: ();
++     scope 1 (inlined callee_forced) {
++     }
+  
+      bb0: {
+          StorageLive(_1);
+-         _1 = callee_forced() -> [return: bb1, unwind continue];
+-     }
+- 
+-     bb1: {
+          StorageDead(_1);
+          _0 = const ();
+          return;
+      }
+  }
+  

tests/mir-opt/inline/forced_dead_code.rs

@@ -0,0 +1,17 @@
+// EMIT_MIT_FOR_EACH_PANIC_STRATEGY
+//@ compile-flags: -Copt-level=0 -Clink-dead-code
+#![feature(rustc_attrs)]
+
+#[rustc_force_inline]
+pub fn callee_forced() {}
+
+// EMIT_MIR forced_dead_code.caller.ForceInline.diff
+pub fn caller() {
+    callee_forced();
+    // CHECK-LABEL: fn caller(
+    // CHECK: (inlined callee_forced)
+}
+
+fn main() {
+    caller();
+}