Hi! We emit a bogus warning on the following testcase, suggesting that the operator should return *this even when it does that already. The problem is that normally cp_build_indirect_ref_1 ensures that *this is folded as current_class_ref, but in templates (if return type is non-dependent, otherwise check_return_expr doesn't check it) it didn't go through cp_build_indirect_ref_1, but just built another INDIRECT_REF. Which means it then doesn't compare pointer-equal to current_class_ref.
The following patch just checks if it is the same thing like cp_build_indirect_ref_1 would check if it would be called. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2021-01-27 Jakub Jelinek <ja...@redhat.com> PR c++/98841 * typeck.c (check_return_expr): If processing_template_decl, don't rely on *this expression being always pointer-equal to current_class_ref. * g++.dg/warn/effc5.C: New test. --- gcc/cp/typeck.c.jj 2021-01-25 10:02:28.380126847 +0100 +++ gcc/cp/typeck.c 2021-01-27 11:21:13.117875551 +0100 @@ -10188,6 +10188,19 @@ check_return_expr (tree retval, bool *no /* Returning '*this' is obviously OK. */ if (retval == current_class_ref) warn = false; + /* In templates, '*this' might not compare pointer equal to + current_class_ref. */ + else if (processing_template_decl + && retval + && TREE_CODE (retval) == INDIRECT_REF + && (TREE_OPERAND (retval, 0) == current_class_ptr + || (TREE_CODE (TREE_OPERAND (retval, 0)) == NOP_EXPR + && (TREE_OPERAND (TREE_OPERAND (retval, 0), 0) + == current_class_ptr) + && (same_type_ignoring_top_level_qualifiers_p + (TREE_TYPE (TREE_OPERAND (retval, 0)), + TREE_TYPE (current_class_ptr)))))) + warn = false; /* If we are calling a function whose return type is the same of the current class reference, it is ok. */ else if (INDIRECT_REF_P (retval) --- gcc/testsuite/g++.dg/warn/effc5.C.jj 2021-01-27 11:24:34.451565246 +0100 +++ gcc/testsuite/g++.dg/warn/effc5.C 2021-01-27 11:23:23.836375556 +0100 @@ -0,0 +1,17 @@ +// PR c++/98841 +// { dg-do compile } +// { dg-options "-Weffc++" } + +struct S { + template <typename T> + S& operator=(const T&) { return *this; } // { dg-bogus "should return a reference to" } + S& operator=(const S&) { return *this; } +}; + +void +foo () +{ + S s, t; + s = 1; + s = t; +} Jakub