@@ -1260,7 +1260,10 @@ finish_return_stmt (tree expr)
r = build_stmt (input_location, RETURN_EXPR, expr);
if (no_warning)
- suppress_warning (r, OPT_Wreturn_type);
+ {
+ suppress_warning (r, OPT_Wreturn_type);
+ suppress_warning (r, OPT_Wdangling_pointer_);
+ }
r = maybe_cleanup_point_expr_void (r);
r = add_stmt (r);
@@ -11273,8 +11273,9 @@ check_return_expr (tree retval, bool *no_warning)
else if (!processing_template_decl
&& maybe_warn_about_returning_address_of_local (retval, loc)
&& INDIRECT_TYPE_P (valtype))
- retval = build2 (COMPOUND_EXPR, TREE_TYPE (retval), retval,
- build_zero_cst (TREE_TYPE (retval)));
+ /* Suppress the Wdangling-pointer warning in the return statement
+ that would otherwise occur. */
+ *no_warning = true;
}
/* A naive attempt to reduce the number of -Wdangling-reference false
@@ -1,11 +1,11 @@
// { dg-do compile { target c++14 } }
// { dg-options "-Wno-return-local-addr" }
-constexpr const int& id(int x) { return x; }
+constexpr const int& id(int x) { return x; } // { dg-message "note: declared here" }
constexpr bool test() {
const int& y = id(3);
return y == 3;
}
-constexpr bool x = test(); // { dg-error "" }
+constexpr bool x = test(); // { dg-error "accessing object outside its lifetime" }
@@ -24,6 +24,3 @@ return_addr_local_as_intref (void)
return (const intptr_t&)a; // { dg-warning "\\\[-Wreturn-local-addr]" } */
}
-
-/* Verify that the return value has been replaced with zero:
- { dg-final { scan-tree-dump-times "return 0;" 2 "optimized" } } */
Currently, when typeck discovers that a return statement will refer to a local variable it rewrites to return a null pointer. This causes the error messages for using the return value in a constant expression to be unhelpful, especially for reference return values. This patch removes this "optimisation". Relying on this raises a warning by default and causes UB anyway, so there should be no issue in doing so. We also suppress additional warnings from later passes that detect this as a dangling pointer, since we've already indicated this anyway. gcc/cp/ChangeLog: * semantics.cc (finish_return_stmt): Suppress dangling pointer reporting on return statement if already reported. * typeck.cc (check_return_expr): Don't set return expression to zero for dangling addresses. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/constexpr-lifetime5.C: Test reported message is correct. * g++.dg/warn/Wreturn-local-addr-6.C: Remove check for return value optimisation. Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com> --- gcc/cp/semantics.cc | 5 ++++- gcc/cp/typeck.cc | 5 +++-- gcc/testsuite/g++.dg/cpp1y/constexpr-lifetime5.C | 4 ++-- gcc/testsuite/g++.dg/warn/Wreturn-local-addr-6.C | 3 --- 4 files changed, 9 insertions(+), 8 deletions(-)