constant: avoid div-by-0 due to ZST arrays/slices.

Author: eddyb

crates/rustc_codegen_spirv/src/codegen_cx/constant.rs

@@ -573,9 +573,10 @@ impl<'tcx> CodegenCx<'tcx> {
                     SpirvType::Array { count, .. } => {
                         u64::try_from(self.builder.lookup_const_scalar(count).unwrap()).unwrap()
                     }
-                    SpirvType::RuntimeArray { .. } => {
-                        (alloc.inner().size() - offset).bytes() / stride.bytes()
-                    }
+                    SpirvType::RuntimeArray { .. } => (alloc.inner().size() - offset)
+                        .bytes()
+                        .checked_div(stride.bytes())
+                        .unwrap_or(0),
                     _ => unreachable!(),
                 };
 

tests/compiletests/ui/lang/core/mem/size_of_val_unsized.stderr

@@ -0,0 +1,23 @@
+error: unsupported unsized `[struct () {  }]` constant
+   |
+   = note: used by unnamed global (%68)
+   = note: used by unnamed global (%69)
+note: used from within `size_of_val_unsized::main`
+  --> <$DIR/size_of_val_unsized.rs>:5:12
+   |
+LL |       *out = core::mem::size_of_val(
+   |  ____________^
+LL | |         const {
+LL | |             struct S<T: ?Sized>(T);
+LL | |             &S([]) as &S<[()]>
+LL | |         },
+LL | |     );
+   | |_____^
+note: called by `main`
+  --> <$DIR/size_of_val_unsized.rs>:4:8
+   |
+LL | pub fn main(out: &mut usize) {
+   |        ^^^^
+
+error: aborting due to 1 previous error
+