From ae32f43c50fc72ba2812c18053c34d1b94aa5e3f Mon Sep 17 00:00:00 2001
From: DrMeepster <19316085+DrMeepster@users.noreply.github.com>
Date: Tue, 15 Feb 2022 19:24:12 -0800
Subject: [PATCH 1/2] fix assumption that ScalarPair Box is always a fat
 pointer

---
 compiler/rustc_codegen_llvm/src/type_of.rs | 2 +-
 src/test/ui/box/issue-78459-ice.rs         | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/box/issue-78459-ice.rs

diff --git a/compiler/rustc_codegen_llvm/src/type_of.rs b/compiler/rustc_codegen_llvm/src/type_of.rs
index 81d0603bc5200..24e158b489bdf 100644
--- a/compiler/rustc_codegen_llvm/src/type_of.rs
+++ b/compiler/rustc_codegen_llvm/src/type_of.rs
@@ -330,7 +330,7 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
             ty::Ref(..) | ty::RawPtr(_) => {
                 return self.field(cx, index).llvm_type(cx);
             }
-            ty::Adt(def, _) if def.is_box() => {
+            ty::Adt(def, substs) if def.is_box() && cx.layout_of(substs.type_at(1)).is_zst() => {
                 let ptr_ty = cx.tcx.mk_mut_ptr(self.ty.boxed_ty());
                 return cx.layout_of(ptr_ty).scalar_pair_element_llvm_type(cx, index, immediate);
             }
diff --git a/src/test/ui/box/issue-78459-ice.rs b/src/test/ui/box/issue-78459-ice.rs
new file mode 100644
index 0000000000000..89f75fea15b1d
--- /dev/null
+++ b/src/test/ui/box/issue-78459-ice.rs
@@ -0,0 +1,6 @@
+// check-pass
+#![feature(allocator_api)]
+
+fn main() {
+    Box::new_in((), &std::alloc::Global);
+}

From d0b508e1a7d7f0408a782193c78e7b2ee052ef3b Mon Sep 17 00:00:00 2001
From: DrMeepster <19316085+DrMeepster@users.noreply.github.com>
Date: Wed, 16 Feb 2022 16:52:06 -0800
Subject: [PATCH 2/2] add comment explaining the check

---
 compiler/rustc_codegen_llvm/src/type_of.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler/rustc_codegen_llvm/src/type_of.rs b/compiler/rustc_codegen_llvm/src/type_of.rs
index 24e158b489bdf..fafb9a6dbdecc 100644
--- a/compiler/rustc_codegen_llvm/src/type_of.rs
+++ b/compiler/rustc_codegen_llvm/src/type_of.rs
@@ -330,6 +330,8 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
             ty::Ref(..) | ty::RawPtr(_) => {
                 return self.field(cx, index).llvm_type(cx);
             }
+            // only wide pointer boxes are handled as pointers
+            // thin pointer boxes with scalar allocators are handled by the general logic below
             ty::Adt(def, substs) if def.is_box() && cx.layout_of(substs.type_at(1)).is_zst() => {
                 let ptr_ty = cx.tcx.mk_mut_ptr(self.ty.boxed_ty());
                 return cx.layout_of(ptr_ty).scalar_pair_element_llvm_type(cx, index, immediate);