Auto merge of #107772 - compiler-errors:dyn-star-backend-is-ptr, r=eholk

Make `dyn*`'s value backend type a pointer

One tweak on top of Ralf's commit should fix using `usize` as a `dyn*`-coercible type, and should fix when we're using various other pointer types when LLVM opaque pointers is disabled.

r? `@eholk` but feel free to reassign
cc https://github.com/rust-lang/rust/pull/107728#issuecomment-1421231823 `@RalfJung`

2 files changed, 86 insertions, 87 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 023d38e9312..4e13d4dbcb7 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -39,7 +39,7 @@ use rustc_session::Session;
 use rustc_span::symbol::sym;
 use rustc_span::Symbol;
 use rustc_span::{DebuggerVisualizerFile, DebuggerVisualizerType};
-use rustc_target::abi::{Align, Size, VariantIdx};
+use rustc_target::abi::{Align, VariantIdx};
 
 use std::collections::BTreeSet;
 use std::time::{Duration, Instant};
@@ -273,12 +273,13 @@ pub fn cast_to_dyn_star<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         matches!(dst_ty.kind(), ty::Dynamic(_, _, ty::DynStar)),
         "destination type must be a dyn*"
     );
-    // FIXME(dyn-star): this is probably not the best way to check if this is
-    // a pointer, and really we should ensure that the value is a suitable
-    // pointer earlier in the compilation process.
-    let src = match src_ty_and_layout.pointee_info_at(bx.cx(), Size::ZERO) {
-        Some(_) => bx.ptrtoint(src, bx.cx().type_isize()),
-        None => bx.bitcast(src, bx.type_isize()),
+    // FIXME(dyn-star): We can remove this when all supported LLVMs use opaque ptrs only.
+    let unit_ptr = bx.cx().type_ptr_to(bx.cx().type_struct(&[], false));
+    let src = match bx.cx().type_kind(bx.cx().backend_type(src_ty_and_layout)) {
+        TypeKind::Pointer => bx.pointercast(src, unit_ptr),
+        TypeKind::Integer => bx.inttoptr(src, unit_ptr),
+        // FIXME(dyn-star): We probably have to do a bitcast first, then inttoptr.
+        kind => bug!("unexpected TypeKind for left-hand side of `dyn*` cast: {kind:?}"),
     };
     (src, unsized_info(bx, src_ty_and_layout.ty, dst_ty, old_info))
 }
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 9af408646ae..daaa4de1a7c 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -452,86 +452,84 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             args1 = [place.llval];
             &args1[..]
         };
-        let (drop_fn, fn_abi) = match ty.kind() {
-            // FIXME(eddyb) perhaps move some of this logic into
-            // `Instance::resolve_drop_in_place`?
-            ty::Dynamic(_, _, ty::Dyn) => {
-                // IN THIS ARM, WE HAVE:
-                // ty = *mut (dyn Trait)
-                // which is: exists<T> ( *mut T,    Vtable<T: Trait> )
-                //                       args[0]    args[1]
-                //
-                // args = ( Data, Vtable )
-                //                  |
-                //                  v
-                //                /-------\
-                //                | ...   |
-                //                \-------/
-                //
-                let virtual_drop = Instance {
-                    def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
-                    substs: drop_fn.substs,
-                };
-                debug!("ty = {:?}", ty);
-                debug!("drop_fn = {:?}", drop_fn);
-                debug!("args = {:?}", args);
-                let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
-                let vtable = args[1];
-                // Truncate vtable off of args list
-                args = &args[..1];
-                (
-                    meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
-                        .get_fn(bx, vtable, ty, &fn_abi),
-                    fn_abi,
-                )
-            }
-            ty::Dynamic(_, _, ty::DynStar) => {
-                // IN THIS ARM, WE HAVE:
-                // ty = *mut (dyn* Trait)
-                // which is: *mut exists<T: sizeof(T) == sizeof(usize)> (T, Vtable<T: Trait>)
-                //
-                // args = [ * ]
-                //          |
-                //          v
-                //      ( Data, Vtable )
-                //                |
-                //                v
-                //              /-------\
-                //              | ...   |
-                //              \-------/
-                //
-                //
-                // WE CAN CONVERT THIS INTO THE ABOVE LOGIC BY DOING
-                //
-                // data = &(*args[0]).0    // gives a pointer to Data above (really the same pointer)
-                // vtable = (*args[0]).1   // loads the vtable out
-                // (data, vtable)          // an equivalent Rust `*mut dyn Trait`
-                //
-                // SO THEN WE CAN USE THE ABOVE CODE.
-                let virtual_drop = Instance {
-                    def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
-                    substs: drop_fn.substs,
-                };
-                debug!("ty = {:?}", ty);
-                debug!("drop_fn = {:?}", drop_fn);
-                debug!("args = {:?}", args);
-                let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
-                let data = args[0];
-                let data_ty = bx.cx().backend_type(place.layout);
-                let vtable_ptr =
-                    bx.gep(data_ty, data, &[bx.cx().const_i32(0), bx.cx().const_i32(1)]);
-                let vtable = bx.load(bx.type_i8p(), vtable_ptr, abi::Align::ONE);
-                // Truncate vtable off of args list
-                args = &args[..1];
-                debug!("args' = {:?}", args);
-                (
-                    meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
-                        .get_fn(bx, vtable, ty, &fn_abi),
-                    fn_abi,
-                )
-            }
-            _ => (bx.get_fn_addr(drop_fn), bx.fn_abi_of_instance(drop_fn, ty::List::empty())),
-        };
+        let (drop_fn, fn_abi) =
+            match ty.kind() {
+                // FIXME(eddyb) perhaps move some of this logic into
+                // `Instance::resolve_drop_in_place`?
+                ty::Dynamic(_, _, ty::Dyn) => {
+                    // IN THIS ARM, WE HAVE:
+                    // ty = *mut (dyn Trait)
+                    // which is: exists<T> ( *mut T,    Vtable<T: Trait> )
+                    //                       args[0]    args[1]
+                    //
+                    // args = ( Data, Vtable )
+                    //                  |
+                    //                  v
+                    //                /-------\
+                    //                | ...   |
+                    //                \-------/
+                    //
+                    let virtual_drop = Instance {
+                        def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
+                        substs: drop_fn.substs,
+                    };
+                    debug!("ty = {:?}", ty);
+                    debug!("drop_fn = {:?}", drop_fn);
+                    debug!("args = {:?}", args);
+                    let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
+                    let vtable = args[1];
+                    // Truncate vtable off of args list
+                    args = &args[..1];
+                    (
+                        meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
+                            .get_fn(bx, vtable, ty, &fn_abi),
+                        fn_abi,
+                    )
+                }
+                ty::Dynamic(_, _, ty::DynStar) => {
+                    // IN THIS ARM, WE HAVE:
+                    // ty = *mut (dyn* Trait)
+                    // which is: *mut exists<T: sizeof(T) == sizeof(usize)> (T, Vtable<T: Trait>)
+                    //
+                    // args = [ * ]
+                    //          |
+                    //          v
+                    //      ( Data, Vtable )
+                    //                |
+                    //                v
+                    //              /-------\
+                    //              | ...   |
+                    //              \-------/
+                    //
+                    //
+                    // WE CAN CONVERT THIS INTO THE ABOVE LOGIC BY DOING
+                    //
+                    // data = &(*args[0]).0    // gives a pointer to Data above (really the same pointer)
+                    // vtable = (*args[0]).1   // loads the vtable out
+                    // (data, vtable)          // an equivalent Rust `*mut dyn Trait`
+                    //
+                    // SO THEN WE CAN USE THE ABOVE CODE.
+                    let virtual_drop = Instance {
+                        def: ty::InstanceDef::Virtual(drop_fn.def_id(), 0),
+                        substs: drop_fn.substs,
+                    };
+                    debug!("ty = {:?}", ty);
+                    debug!("drop_fn = {:?}", drop_fn);
+                    debug!("args = {:?}", args);
+                    let fn_abi = bx.fn_abi_of_instance(virtual_drop, ty::List::empty());
+                    let meta_ptr = place.project_field(bx, 1);
+                    let meta = bx.load_operand(meta_ptr);
+                    // Truncate vtable off of args list
+                    args = &args[..1];
+                    debug!("args' = {:?}", args);
+                    (
+                        meth::VirtualIndex::from_index(ty::COMMON_VTABLE_ENTRIES_DROPINPLACE)
+                            .get_fn(bx, meta.immediate(), ty, &fn_abi),
+                        fn_abi,
+                    )
+                }
+                _ => (bx.get_fn_addr(drop_fn), bx.fn_abi_of_instance(drop_fn, ty::List::empty())),
+            };
         helper.do_call(
             self,
             bx,