Rollup merge of #100887 - eholk:codegen_call_terminator-cleanup, r=fee1-dead

Refactor part of codegen_call_terminator

I was reading through this code and found the chain of `if let` and a nested match on the same value that was matched in the `if let` to be kind of hard to follow. This PR cleans it up by flattening the `if let` chain and nested match into a single `match` expression.

Author: matthiaskrgr

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -798,58 +798,55 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             let mut op = self.codegen_operand(&mut bx, arg);
 
             if let (0, Some(ty::InstanceDef::Virtual(_, idx))) = (i, def) {
-                if let Pair(..) = op.val {
-                    // In the case of Rc<Self>, we need to explicitly pass a
-                    // *mut RcBox<Self> with a Scalar (not ScalarPair) ABI. This is a hack
-                    // that is understood elsewhere in the compiler as a method on
-                    // `dyn Trait`.
-                    // To get a `*mut RcBox<Self>`, we just keep unwrapping newtypes until
-                    // we get a value of a built-in pointer type
-                    'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
-                        && !op.layout.ty.is_region_ptr()
-                    {
-                        for i in 0..op.layout.fields.count() {
-                            let field = op.extract_field(&mut bx, i);
-                            if !field.layout.is_zst() {
-                                // we found the one non-zero-sized field that is allowed
-                                // now find *its* non-zero-sized field, or stop if it's a
-                                // pointer
-                                op = field;
-                                continue 'descend_newtypes;
+                match op.val {
+                    Pair(data_ptr, meta) => {
+                        // In the case of Rc<Self>, we need to explicitly pass a
+                        // *mut RcBox<Self> with a Scalar (not ScalarPair) ABI. This is a hack
+                        // that is understood elsewhere in the compiler as a method on
+                        // `dyn Trait`.
+                        // To get a `*mut RcBox<Self>`, we just keep unwrapping newtypes until
+                        // we get a value of a built-in pointer type
+                        'descend_newtypes: while !op.layout.ty.is_unsafe_ptr()
+                            && !op.layout.ty.is_region_ptr()
+                        {
+                            for i in 0..op.layout.fields.count() {
+                                let field = op.extract_field(&mut bx, i);
+                                if !field.layout.is_zst() {
+                                    // we found the one non-zero-sized field that is allowed
+                                    // now find *its* non-zero-sized field, or stop if it's a
+                                    // pointer
+                                    op = field;
+                                    continue 'descend_newtypes;
+                                }
                             }
+
+                            span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
                         }
 
-                        span_bug!(span, "receiver has no non-zero-sized fields {:?}", op);
+                        // now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
+                        // data pointer and vtable. Look up the method in the vtable, and pass
+                        // the data pointer as the first argument
+                        llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
+                            &mut bx,
+                            meta,
+                            op.layout.ty,
+                            &fn_abi,
+                        ));
+                        llargs.push(data_ptr);
+                        continue 'make_args;
                     }
-
-                    // now that we have `*dyn Trait` or `&dyn Trait`, split it up into its
-                    // data pointer and vtable. Look up the method in the vtable, and pass
-                    // the data pointer as the first argument
-                    match op.val {
-                        Pair(data_ptr, meta) => {
-                            llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
-                                &mut bx,
-                                meta,
-                                op.layout.ty,
-                                &fn_abi,
-                            ));
-                            llargs.push(data_ptr);
-                            continue 'make_args;
-                        }
-                        other => bug!("expected a Pair, got {:?}", other),
+                    Ref(data_ptr, Some(meta), _) => {
+                        // by-value dynamic dispatch
+                        llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
+                            &mut bx,
+                            meta,
+                            op.layout.ty,
+                            &fn_abi,
+                        ));
+                        llargs.push(data_ptr);
+                        continue;
                     }
-                } else if let Ref(data_ptr, Some(meta), _) = op.val {
-                    // by-value dynamic dispatch
-                    llfn = Some(meth::VirtualIndex::from_index(idx).get_fn(
-                        &mut bx,
-                        meta,
-                        op.layout.ty,
-                        &fn_abi,
-                    ));
-                    llargs.push(data_ptr);
-                    continue;
-                } else {
-                    span_bug!(span, "can't codegen a virtual call on {:?}", op);
+                    _ => span_bug!(span, "can't codegen a virtual call on {:?}", op),
                 }
             }