diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs index 2b7d9be6d350b..1002746e553d7 100644 --- a/compiler/rustc_mir_transform/src/gvn.rs +++ b/compiler/rustc_mir_transform/src/gvn.rs @@ -1391,11 +1391,15 @@ fn op_to_prop_const<'tcx>( let (prov, offset) = pointer.into_parts(); let alloc_id = prov.alloc_id(); intern_const_alloc_for_constprop(ecx, alloc_id).ok()?; - if matches!(ecx.tcx.global_alloc(alloc_id), GlobalAlloc::Memory(_)) { - // `alloc_id` may point to a static. Codegen will choke on an `Indirect` with anything - // by `GlobalAlloc::Memory`, so do fall through to copying if needed. - // FIXME: find a way to treat this more uniformly - // (probably by fixing codegen) + + // `alloc_id` may point to a static. Codegen will choke on an `Indirect` with anything + // by `GlobalAlloc::Memory`, so do fall through to copying if needed. + // FIXME: find a way to treat this more uniformly (probably by fixing codegen) + if let GlobalAlloc::Memory(alloc) = ecx.tcx.global_alloc(alloc_id) + // Transmuting a constant is just an offset in the allocation. If the alignment of the + // allocation is not enough, fallback to copying into a properly aligned value. + && alloc.inner().align >= op.layout.align.abi + { return Some(ConstValue::Indirect { alloc_id, offset }); } } diff --git a/tests/ui/mir/alignment/misaligned-constant-gvn.rs b/tests/ui/mir/alignment/misaligned-constant-gvn.rs new file mode 100644 index 0000000000000..363d5c0ed34c6 --- /dev/null +++ b/tests/ui/mir/alignment/misaligned-constant-gvn.rs @@ -0,0 +1,8 @@ +//@ build-pass +//@ compile-flags: -Zmir-opt-level=0 -Zmir-enable-passes=+GVN + +fn main() { + let variant: Option = None; + let transmuted: u64 = unsafe { std::mem::transmute(variant) }; + println!("{transmuted}"); +}