From 3c8563abcf91eda340aa77d238954dd00fa0cb34 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sat, 6 Aug 2022 17:18:59 -0400 Subject: make NOP dyn casts not require anything about the vtable --- compiler/rustc_codegen_cranelift/src/unsize.rs | 1 + compiler/rustc_codegen_ssa/src/base.rs | 1 + compiler/rustc_const_eval/src/interpret/cast.rs | 7 ++++++- 3 files changed, 8 insertions(+), 1 deletion(-) (limited to 'compiler') diff --git a/compiler/rustc_codegen_cranelift/src/unsize.rs b/compiler/rustc_codegen_cranelift/src/unsize.rs index 052ca0a082b..dd9d891ddbd 100644 --- a/compiler/rustc_codegen_cranelift/src/unsize.rs +++ b/compiler/rustc_codegen_cranelift/src/unsize.rs @@ -29,6 +29,7 @@ pub(crate) fn unsized_info<'tcx>( let old_info = old_info.expect("unsized_info: missing old info for trait upcasting coercion"); if data_a.principal_def_id() == data_b.principal_def_id() { + // A NOP cast that doesn't actually change anything, should be allowed even with invalid vtables. return old_info; } diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs index a840b270974..4c6be3f9108 100644 --- a/compiler/rustc_codegen_ssa/src/base.rs +++ b/compiler/rustc_codegen_ssa/src/base.rs @@ -151,6 +151,7 @@ pub fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( let old_info = old_info.expect("unsized_info: missing old info for trait upcasting coercion"); if data_a.principal_def_id() == data_b.principal_def_id() { + // A NOP cast that doesn't actually change anything, should be allowed even with invalid vtables. return old_info; } diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs index c97c31eb9da..14eb2a1537b 100644 --- a/compiler/rustc_const_eval/src/interpret/cast.rs +++ b/compiler/rustc_const_eval/src/interpret/cast.rs @@ -298,7 +298,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { self.write_immediate(val, dest) } (&ty::Dynamic(ref data_a, ..), &ty::Dynamic(ref data_b, ..)) => { - let (old_data, old_vptr) = self.read_immediate(src)?.to_scalar_pair()?; + let val = self.read_immediate(src)?; + if data_a.principal() == data_b.principal() { + // A NOP cast that doesn't actually change anything, should be allowed even with mismatching vtables. + return self.write_immediate(*val, dest); + } + let (old_data, old_vptr) = val.to_scalar_pair()?; let old_vptr = old_vptr.to_pointer(self)?; let (ty, old_trait) = self.get_ptr_vtable(old_vptr)?; if old_trait != data_a.principal() { -- cgit 1.4.1-3-g733a5