From d8ed2fb0bb8aecfe7622134d5aba7b670056ee6d Mon Sep 17 00:00:00 2001
From: Jakob Degen <jakob.e.degen@gmail.com>
Date: Tue, 4 Apr 2023 23:07:10 -0700
Subject: [PATCH] Fix transmute intrinsic mir validation ICE

---
 .../rustc_const_eval/src/transform/validate.rs  | 12 ++++++++++--
 tests/ui/mir/validate/transmute_cast_sized.rs   | 17 +++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 tests/ui/mir/validate/transmute_cast_sized.rs

diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 0f56fda18f5..d4bed97380b 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -679,13 +679,21 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                             // Unlike `mem::transmute`, a MIR `Transmute` is well-formed
                             // for any two `Sized` types, just potentially UB to run.
 
-                            if !op_ty.is_sized(self.tcx, self.param_env) {
+                            if !self
+                                .tcx
+                                .normalize_erasing_regions(self.param_env, op_ty)
+                                .is_sized(self.tcx, self.param_env)
+                            {
                                 self.fail(
                                     location,
                                     format!("Cannot transmute from non-`Sized` type {op_ty:?}"),
                                 );
                             }
-                            if !target_type.is_sized(self.tcx, self.param_env) {
+                            if !self
+                                .tcx
+                                .normalize_erasing_regions(self.param_env, *target_type)
+                                .is_sized(self.tcx, self.param_env)
+                            {
                                 self.fail(
                                     location,
                                     format!("Cannot transmute to non-`Sized` type {target_type:?}"),
diff --git a/tests/ui/mir/validate/transmute_cast_sized.rs b/tests/ui/mir/validate/transmute_cast_sized.rs
new file mode 100644
index 00000000000..eaaf7eb3ecd
--- /dev/null
+++ b/tests/ui/mir/validate/transmute_cast_sized.rs
@@ -0,0 +1,17 @@
+// build-pass
+// compile-flags: -Zvalidate-mir
+// edition: 2021
+
+#![crate_type = "lib"]
+
+// Use `PhantomData` to get target-independent size
+async fn get(_r: std::marker::PhantomData<&i32>) {
+    loop {}
+}
+
+pub fn check() {
+    let mut v = get(loop {});
+    let _ = || unsafe {
+        v = std::mem::transmute([0_u8; 1]);
+    };
+}