fix ices on vfe about principal trait

compiler/rustc_codegen_ssa/src/base.rs

@@ -37,6 +37,7 @@ use crate::back::write::{
     submit_post_lto_module_to_llvm, submit_pre_lto_module_to_llvm, ComputedLtoType, OngoingCodegen,
 };
 use crate::common::{self, IntPredicate, RealPredicate, TypeKind};
+use crate::meth::load_vtable;
 use crate::mir::operand::OperandValue;
 use crate::mir::place::PlaceRef;
 use crate::traits::*;
@@ -135,14 +136,8 @@ fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
             if let Some(entry_idx) = vptr_entry_idx {
                 let ptr_size = bx.data_layout().pointer_size;
-                let ptr_align = bx.data_layout().pointer_align.abi;
                 let vtable_byte_offset = u64::try_from(entry_idx).unwrap() * ptr_size.bytes();
-                let gep = bx.inbounds_ptradd(old_info, bx.const_usize(vtable_byte_offset));
-                let new_vptr = bx.load(bx.type_ptr(), gep, ptr_align);
-                bx.nonnull_metadata(new_vptr);
-                // VTable loads are invariant.
-                bx.set_invariant_load(new_vptr);
-                new_vptr
+                load_vtable(bx, old_info, bx.type_ptr(), vtable_byte_offset, source, true)
             } else {
                 old_info
             }

compiler/rustc_codegen_ssa/src/meth.rs

@@ -28,27 +28,9 @@ impl<'a, 'tcx> VirtualIndex {
 
         let llty = bx.fn_ptr_backend_type(fn_abi);
         let ptr_size = bx.data_layout().pointer_size;
-        let ptr_align = bx.data_layout().pointer_align.abi;
         let vtable_byte_offset = self.0 * ptr_size.bytes();
 
-        if bx.cx().sess().opts.unstable_opts.virtual_function_elimination
-            && bx.cx().sess().lto() == Lto::Fat
-        {
-            let typeid = bx
-                .typeid_metadata(typeid_for_trait_ref(bx.tcx(), expect_dyn_trait_in_self(ty)))
-                .unwrap();
-            let func = bx.type_checked_load(llvtable, vtable_byte_offset, typeid);
-            func
-        } else {
-            let gep = bx.inbounds_ptradd(llvtable, bx.const_usize(vtable_byte_offset));
-            let ptr = bx.load(llty, gep, ptr_align);
-            // VTable loads are invariant.
-            bx.set_invariant_load(ptr);
-            if nonnull {
-                bx.nonnull_metadata(ptr);
-            }
-            ptr
-        }
+        load_vtable(bx, llvtable, llty, vtable_byte_offset, ty, nonnull)
     }
 
     pub(crate) fn get_optional_fn<Bx: BuilderMethods<'a, 'tcx>>(
@@ -75,31 +57,27 @@ impl<'a, 'tcx> VirtualIndex {
         self,
         bx: &mut Bx,
         llvtable: Bx::Value,
+        ty: Ty<'tcx>,
     ) -> Bx::Value {
         // Load the data pointer from the object.
         debug!("get_int({:?}, {:?})", llvtable, self);
 
         let llty = bx.type_isize();
         let ptr_size = bx.data_layout().pointer_size;
-        let ptr_align = bx.data_layout().pointer_align.abi;
         let vtable_byte_offset = self.0 * ptr_size.bytes();
 
-        let gep = bx.inbounds_ptradd(llvtable, bx.const_usize(vtable_byte_offset));
-        let ptr = bx.load(llty, gep, ptr_align);
-        // VTable loads are invariant.
-        bx.set_invariant_load(ptr);
-        ptr
+        load_vtable(bx, llvtable, llty, vtable_byte_offset, ty, false)
     }
 }
 
 /// This takes a valid `self` receiver type and extracts the principal trait
-/// ref of the type.
-fn expect_dyn_trait_in_self(ty: Ty<'_>) -> ty::PolyExistentialTraitRef<'_> {
+/// ref of the type. Return `None` if there is no principal trait.
+fn dyn_trait_in_self(ty: Ty<'_>) -> Option<ty::PolyExistentialTraitRef<'_>> {
     for arg in ty.peel_refs().walk() {
         if let GenericArgKind::Type(ty) = arg.unpack()
             && let ty::Dynamic(data, _, _) = ty.kind()
         {
-            return data.principal().expect("expected principal trait object");
+            return data.principal();
         }
     }
 
@@ -138,3 +116,36 @@ pub(crate) fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
     cx.vtables().borrow_mut().insert((ty, trait_ref), vtable);
     vtable
 }
+
+/// Call this function whenever you need to load a vtable.
+pub(crate) fn load_vtable<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
+    bx: &mut Bx,
+    llvtable: Bx::Value,
+    llty: Bx::Type,
+    vtable_byte_offset: u64,
+    ty: Ty<'tcx>,
+    nonnull: bool,
+) -> Bx::Value {
+    let ptr_align = bx.data_layout().pointer_align.abi;
+
+    if bx.cx().sess().opts.unstable_opts.virtual_function_elimination
+        && bx.cx().sess().lto() == Lto::Fat
+    {
+        if let Some(trait_ref) = dyn_trait_in_self(ty) {
+            let typeid = bx.typeid_metadata(typeid_for_trait_ref(bx.tcx(), trait_ref)).unwrap();
+            let func = bx.type_checked_load(llvtable, vtable_byte_offset, typeid);
+            return func;
+        } else if nonnull {
+            bug!("load nonnull value from a vtable without a principal trait")
+        }
+    }
+
+    let gep = bx.inbounds_ptradd(llvtable, bx.const_usize(vtable_byte_offset));
+    let ptr = bx.load(llty, gep, ptr_align);
+    // VTable loads are invariant.
+    bx.set_invariant_load(ptr);
+    if nonnull {
+        bx.nonnull_metadata(ptr);
+    }
+    ptr
+}

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -126,7 +126,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     sym::vtable_align => ty::COMMON_VTABLE_ENTRIES_ALIGN,
                     _ => bug!(),
                 };
-                let value = meth::VirtualIndex::from_index(idx).get_usize(bx, vtable);
+                let value = meth::VirtualIndex::from_index(idx).get_usize(bx, vtable, callee_ty);
                 match name {
                     // Size is always <= isize::MAX.
                     sym::vtable_size => {

compiler/rustc_codegen_ssa/src/size_of_val.rs

@@ -28,9 +28,9 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
             // Load size/align from vtable.
             let vtable = info.unwrap();
             let size = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_SIZE)
-                .get_usize(bx, vtable);
+                .get_usize(bx, vtable, t);
             let align = meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_ALIGN)
-                .get_usize(bx, vtable);
+                .get_usize(bx, vtable, t);
 
             // Size is always <= isize::MAX.
             let size_bound = bx.data_layout().ptr_sized_integer().signed_max() as u128;

tests/ui/codegen/virtual-function-elimination.rs

@@ -0,0 +1,17 @@
+//@ build-pass
+//@ compile-flags: -Zvirtual-function-elimination=true -Clto=true
+//@ only-x86_64
+//@ no-prefer-dynamic
+
+// issue #123955
+pub fn test0() {
+    _ = Box::new(()) as Box<dyn Send>;
+}
+
+// issue #124092
+const X: for<'b> fn(&'b ()) = |&()| ();
+pub fn test1() {
+    let _dyn_debug = Box::new(X) as Box<fn(&'static ())> as Box<dyn Send>;
+}
+
+fn main() {}