From dabcfff40df5b1edbfca8bd808250f0130c81b7f Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Thu, 15 Jun 2023 18:02:55 -0400
Subject: [PATCH 1/2] Disable alignment checks on i686-pc-windows-msvc

---
 .../src/check_alignment.rs                    |  3 +++
 ...ir_alignment_check_i686-pc-windows-msvc.rs | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 tests/ui/mir/mir_alignment_check_i686-pc-windows-msvc.rs

diff --git a/compiler/rustc_mir_transform/src/check_alignment.rs b/compiler/rustc_mir_transform/src/check_alignment.rs
index 1fe8ea0789286..d7141b91bc135 100644
--- a/compiler/rustc_mir_transform/src/check_alignment.rs
+++ b/compiler/rustc_mir_transform/src/check_alignment.rs
@@ -14,6 +14,9 @@ pub struct CheckAlignment;
 
 impl<'tcx> MirPass<'tcx> for CheckAlignment {
     fn is_enabled(&self, sess: &Session) -> bool {
+        if sess.target.llvm_target == "i686-pc-windows-msvc" {
+            return false;
+        }
         sess.opts.debug_assertions
     }
 
diff --git a/tests/ui/mir/mir_alignment_check_i686-pc-windows-msvc.rs b/tests/ui/mir/mir_alignment_check_i686-pc-windows-msvc.rs
new file mode 100644
index 0000000000000..56388c1047e9a
--- /dev/null
+++ b/tests/ui/mir/mir_alignment_check_i686-pc-windows-msvc.rs
@@ -0,0 +1,21 @@
+// run-pass
+// only-i686-pc-windows-msvc
+// compile-flags: -Copt-level=0 -Cdebug-assertions=yes
+
+// MSVC isn't sure if on 32-bit Windows its u64 type is 8-byte-aligned or 4-byte-aligned.
+// So this test ensures that on i686-pc-windows-msvc, we do not insert a runtime check
+// that will fail on dereferencing of a pointer to u64 which is not 8-byte-aligned but is
+// 4-byte-aligned.
+
+#![feature(strict_provenance)]
+
+fn main() {
+    let mut x = [0u64; 2];
+    let ptr: *mut u8 = x.as_mut_ptr().cast::<u8>();
+    unsafe {
+        let misaligned = ptr.add(4).cast::<u64>();
+        assert!(misaligned.addr() % 8 != 0);
+        assert!(misaligned.addr() % 4 == 0);
+        *misaligned = 42;
+    }
+}

From 55d680b4128007c34a328ffc3e4346ff6ae1d9cd Mon Sep 17 00:00:00 2001
From: Wesley Wiser <wwiser@gmail.com>
Date: Thu, 15 Jun 2023 19:48:06 -0400
Subject: [PATCH 2/2] Update
 compiler/rustc_mir_transform/src/check_alignment.rs

---
 compiler/rustc_mir_transform/src/check_alignment.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/compiler/rustc_mir_transform/src/check_alignment.rs b/compiler/rustc_mir_transform/src/check_alignment.rs
index d7141b91bc135..ea07806887ae8 100644
--- a/compiler/rustc_mir_transform/src/check_alignment.rs
+++ b/compiler/rustc_mir_transform/src/check_alignment.rs
@@ -14,6 +14,7 @@ pub struct CheckAlignment;
 
 impl<'tcx> MirPass<'tcx> for CheckAlignment {
     fn is_enabled(&self, sess: &Session) -> bool {
+        // FIXME(#112480) MSVC and rustc disagree on minimum stack alignment on x86 Windows
         if sess.target.llvm_target == "i686-pc-windows-msvc" {
             return false;
         }