Fix to make the test zst_no_llvm_alloc pass

Author: antoyo

src/common.rs

@@ -265,6 +265,19 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
                 let alloc_id = prov.alloc_id();
                 let base_addr = match self.tcx.global_alloc(alloc_id) {
                     GlobalAlloc::Memory(alloc) => {
+                        // For ZSTs directly codegen an aligned pointer.
+                        // This avoids generating a zero-sized constant value and actually needing a
+                        // real address at runtime.
+                        if alloc.inner().len() == 0 {
+                            assert_eq!(offset.bytes(), 0);
+                            let val = self.const_usize(alloc.inner().align.bytes());
+                            return if matches!(layout.primitive(), Pointer(_)) {
+                                self.context.new_cast(None, val, ty)
+                            } else {
+                                self.const_bitcast(val, ty)
+                            };
+                        }
+
                         let init = self.const_data_from_alloc(alloc);
                         let alloc = alloc.inner();
                         let value = match alloc.mutability {

src/consts.rs

@@ -330,7 +330,7 @@ pub(crate) fn const_alloc_to_gcc_uncached<'gcc>(
             // and we properly interpret the provenance as a relocation pointer offset.
             alloc.inspect_with_uninit_and_ptr_outside_interpreter(offset..(offset + pointer_size)),
         )
-        .expect("const_alloc_to_llvm: could not read relocation pointer")
+        .expect("const_alloc_to_gcc_uncached: could not read relocation pointer")
             as u64;
 
         let address_space = cx.tcx.global_alloc(alloc_id).address_space(cx);

tests/failing-ui-tests.txt

@@ -56,7 +56,6 @@ tests/ui/sanitizer/kcfi-mangling.rs
 tests/ui/statics/const_generics.rs
 tests/ui/backtrace/dylib-dep.rs
 tests/ui/delegation/fn-header.rs
-tests/ui/consts/zst_no_llvm_alloc.rs
 tests/ui/consts/const-eval/parse_ints.rs
 tests/ui/simd/intrinsic/generic-as.rs
 tests/ui/runtime/rt-explody-panic-payloads.rs