Fold length constant in Rvalue::Repeat

compiler/rustc_middle/src/mir/type_foldable.rs

@@ -175,7 +175,7 @@ impl<'tcx> TypeFoldable<'tcx> for Rvalue<'tcx> {
         use crate::mir::Rvalue::*;
         match *self {
             Use(ref op) => Use(op.fold_with(folder)),
-            Repeat(ref op, len) => Repeat(op.fold_with(folder), len),
+            Repeat(ref op, len) => Repeat(op.fold_with(folder), len.fold_with(folder)),
             ThreadLocalRef(did) => ThreadLocalRef(did.fold_with(folder)),
             Ref(region, bk, ref place) => {
                 Ref(region.fold_with(folder), bk, place.fold_with(folder))

src/test/ui/mir/issue-76248.rs

@@ -0,0 +1,29 @@
+// This used to ICE during codegen after MIR inlining of g into f.
+// The root cause was a missing fold of length constant in Rvalue::Repeat.
+// Regression test for #76248.
+//
+// build-pass
+// compile-flags: -Zmir-opt-level=2
+
+const N: usize = 1;
+
+pub struct Elem<M> {
+    pub x: [usize; N],
+    pub m: M,
+}
+
+pub fn f() -> Elem<()> {
+    g(())
+}
+
+#[inline]
+pub fn g<M>(m: M) -> Elem<M> {
+    Elem {
+        x: [0; N],
+        m,
+    }
+}
+
+pub fn main() {
+    f();
+}