Rollup merge of rust-lang#137894 - compiler-errors:no-scalar-pair-opt, r=oli-obk

Revert "store ScalarPair via memset when one side is undef and the other side can be memset"

cc rust-lang#137892
reverts rust-lang#135335

r? oli-obk

Author: matthiaskrgr

src/common.rs

@@ -64,11 +64,6 @@ impl<'gcc, 'tcx> ConstCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         if type_is_pointer(typ) { self.context.new_null(typ) } else { self.const_int(typ, 0) }
     }
 
-    fn is_undef(&self, _val: RValue<'gcc>) -> bool {
-        // FIXME: actually check for undef
-        false
-    }
-
     fn const_undef(&self, typ: Type<'gcc>) -> RValue<'gcc> {
         let local = self.current_func.borrow().expect("func").new_local(None, typ, "undefined");
         if typ.is_struct().is_some() {