Auto merge of #54693 - RalfJung:ctfe-scalar-pair-undef, r=oli-obk

do not normalize all non-scalar constants to a ConstValue::ScalarPair

We still need `ConstValue::ScalarPair` for match handling (matching slices and strings), but that will never see anything `Undef`. For non-fat-ptr `ScalarPair`, just point to the allocation like larger data structures do.

Fixes https://github.com/rust-lang/rust/issues/54387

r? @eddyb

1 files changed, 7 insertions, 11 deletions

diff --git a/src/librustc_codegen_llvm/mir/operand.rs b/src/librustc_codegen_llvm/mir/operand.rs
index bfa0e0a451e..ab43531240f 100644
--- a/src/librustc_codegen_llvm/mir/operand.rs
+++ b/src/librustc_codegen_llvm/mir/operand.rs
@@ -8,9 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use rustc::mir::interpret::ConstEvalErr;
+use rustc::mir::interpret::{ConstValue, ConstEvalErr};
 use rustc::mir;
-use rustc::mir::interpret::{ConstValue, ScalarMaybeUndef};
 use rustc::ty;
 use rustc::ty::layout::{self, Align, LayoutOf, TyLayout};
 use rustc_data_structures::sync::Lrc;
@@ -114,15 +113,12 @@ impl OperandRef<'ll, 'tcx> {
                     layout.scalar_pair_element_llvm_type(bx.cx, 0, true),
                 );
                 let b_layout = layout.scalar_pair_element_llvm_type(bx.cx, 1, true);
-                let b_llval = match b {
-                    ScalarMaybeUndef::Scalar(b) => scalar_to_llvm(
-                        bx.cx,
-                        b,
-                        b_scalar,
-                        b_layout,
-                    ),
-                    ScalarMaybeUndef::Undef => C_undef(b_layout),
-                };
+                let b_llval = scalar_to_llvm(
+                    bx.cx,
+                    b,
+                    b_scalar,
+                    b_layout,
+                );
                 OperandValue::Pair(a_llval, b_llval)
             },
             ConstValue::ByRef(_, alloc, offset) => {