From 9389373127705dd4ceb460e6e152cfb9126e6be5 Mon Sep 17 00:00:00 2001
From: Camille GILLOT <gillot.camille@gmail.com>
Date: Sat, 23 Sep 2023 07:23:14 +0000
Subject: [PATCH] Do not transmute immediates to non-immediates.

---
 compiler/rustc_mir_transform/src/gvn.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index 7800aa637292..60ff1dd0d782 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -443,6 +443,16 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 CastKind::Transmute => {
                     let value = self.evaluated[value].as_ref()?;
                     let to = self.ecx.layout_of(to).ok()?;
+                    // `offset` for immediates only supports scalar/scalar-pair ABIs,
+                    // so bail out if the target is not one.
+                    if value.as_mplace_or_imm().is_right() {
+                        match to.abi {
+                            Abi::Scalar(..) | Abi::ScalarPair(..) => {}
+                            _ if to.is_zst() => {}
+                            Abi::Aggregate { .. } if to.fields.count() == 0 => {}
+                            _ => return None,
+                        }
+                    }
                     value.offset(Size::ZERO, to, &self.ecx).ok()?
                 }
                 _ => return None,