Auto merge of #146614 - Zalathar:rollup-hcxvdi1, r=Zalathar

Rollup of 9 pull requests

Successful merges:

 - rust-lang/rust#145095 (Migrate `UnsizedConstParamTy`  to unstable impl of `ConstParamTy_`)
 - rust-lang/rust#145960 (Split `FnCtxt::report_args_error` into subfunctions)
 - rust-lang/rust#146402 (interpret: fix overlapping aggregate initialization)
 - rust-lang/rust#146466 (llvm-wrapper: other cleanup)
 - rust-lang/rust#146574 (compiletest: Enable new-output-capture by default)
 - rust-lang/rust#146599 (replace some `#[const_trait]` with `const trait`)
 - rust-lang/rust#146601 (compiletest: Make `./x test --test-args ...` work again)
 - rust-lang/rust#146608 (improve internal bootstrap docs)
 - rust-lang/rust#146609 (bootstrap: lower verbosity of cargo to one less than bootstrap's)

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 10 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index f6f2e3f2a3a..f8755874014 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -1,5 +1,5 @@
 use itertools::Itertools as _;
-use rustc_abi::{self as abi, FIRST_VARIANT};
+use rustc_abi::{self as abi, BackendRepr, FIRST_VARIANT};
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
@@ -25,6 +25,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         match *rvalue {
             mir::Rvalue::Use(ref operand) => {
                 let cg_operand = self.codegen_operand(bx, operand);
+                // Crucially, we do *not* use `OperandValue::Ref` for types with
+                // `BackendRepr::Scalar | BackendRepr::ScalarPair`. This ensures we match the MIR
+                // semantics regarding when assignment operators allow overlap of LHS and RHS.
+                if matches!(
+                    cg_operand.layout.backend_repr,
+                    BackendRepr::Scalar(..) | BackendRepr::ScalarPair(..),
+                ) {
+                    debug_assert!(!matches!(cg_operand.val, OperandValue::Ref(..)));
+                }
                 // FIXME: consider not copying constants through stack. (Fixable by codegen'ing
                 // constants into `OperandValue::Ref`; why don’t we do that yet if we don’t?)
                 cg_operand.val.store(bx, dest);