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From: Jason Merrill <jason@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-23] c++: Add diagnostic when operator= is used as truth cond [PR25689] Date: Fri, 29 Apr 2022 02:59:10 +0000 (GMT) [thread overview] Message-ID: <20220429025910.158113858D28@sourceware.org> (raw) https://gcc.gnu.org/g:654f6978cdc85a3970ff2c478d4df3e55cf4d3ab commit r13-23-g654f6978cdc85a3970ff2c478d4df3e55cf4d3ab Author: Zhao Wei Liew <zhaoweiliew@gmail.com> Date: Tue Feb 15 17:44:29 2022 +0800 c++: Add diagnostic when operator= is used as truth cond [PR25689] When compiling the following code with g++ -Wparentheses, GCC does not warn on the if statement. For example, there is no warning for this code: struct A { A& operator=(int); operator bool(); }; void f(A a) { if (a = 0); // no warning } This is because a = 0 is a call to operator=, which GCC does not handle. This patch fixes this issue by handling calls to operator= when deciding to warn. Bootstrapped and regression tested on x86_64-pc-linux-gnu. PR c++/25689 gcc/cp/ChangeLog: * call.cc (extract_call_expr): Return a NULL_TREE on failure instead of asserting. (build_new_method_call): Suppress -Wparentheses diagnostic for MODIFY_EXPR. * semantics.cc (is_assignment_op_expr_p): Add function to check if an expression is a call to an op= operator expression. (maybe_convert_cond): Handle the case of a op= operator expression for the -Wparentheses diagnostic. gcc/testsuite/ChangeLog: * g++.dg/warn/Wparentheses-31.C: New test. Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com> Diff: --- gcc/cp/call.cc | 13 +++++-- gcc/cp/semantics.cc | 22 ++++++++++- gcc/testsuite/g++.dg/warn/Wparentheses-31.C | 59 +++++++++++++++++++++++++++++ 3 files changed, 90 insertions(+), 4 deletions(-) diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index fa18d7f8f9d..959279d6216 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -7111,9 +7111,10 @@ extract_call_expr (tree call) default:; } - gcc_assert (TREE_CODE (call) == CALL_EXPR - || TREE_CODE (call) == AGGR_INIT_EXPR - || call == error_mark_node); + if (TREE_CODE (call) != CALL_EXPR + && TREE_CODE (call) != AGGR_INIT_EXPR + && call != error_mark_node) + return NULL_TREE; return call; } @@ -11180,6 +11181,12 @@ build_new_method_call (tree instance, tree fns, vec<tree, va_gc> **args, *fn_p = fn; /* Build the actual CALL_EXPR. */ call = build_over_call (cand, flags, complain); + + /* Suppress warnings for if (my_struct.operator= (x)) where + my_struct is implicitly converted to bool. */ + if (TREE_CODE (call) == MODIFY_EXPR) + suppress_warning (call, OPT_Wparentheses); + /* In an expression of the form `a->f()' where `f' turns out to be a static member function, `a' is none-the-less evaluated. */ diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc index ab48f11c9be..9567559c962 100644 --- a/gcc/cp/semantics.cc +++ b/gcc/cp/semantics.cc @@ -826,6 +826,26 @@ finish_goto_stmt (tree destination) return add_stmt (build_stmt (input_location, GOTO_EXPR, destination)); } +/* Returns true if CALL is a (possibly wrapped) CALL_EXPR or AGGR_INIT_EXPR + to operator= () that is written as an operator expression. */ +static bool +is_assignment_op_expr_p (tree call) +{ + if (call == NULL_TREE) + return false; + + call = extract_call_expr (call); + if (call == NULL_TREE + || call == error_mark_node + || !CALL_EXPR_OPERATOR_SYNTAX (call)) + return false; + + tree fndecl = cp_get_callee_fndecl_nofold (call); + return fndecl != NULL_TREE + && DECL_ASSIGNMENT_OPERATOR_P (fndecl) + && DECL_OVERLOADED_OPERATOR_IS (fndecl, NOP_EXPR); +} + /* COND is the condition-expression for an if, while, etc., statement. Convert it to a boolean value, if appropriate. In addition, verify sequence points if -Wsequence-point is enabled. */ @@ -847,7 +867,7 @@ maybe_convert_cond (tree cond) /* Do the conversion. */ cond = convert_from_reference (cond); - if (TREE_CODE (cond) == MODIFY_EXPR + if ((TREE_CODE (cond) == MODIFY_EXPR || is_assignment_op_expr_p (cond)) && warn_parentheses && !warning_suppressed_p (cond, OPT_Wparentheses) && warning_at (cp_expr_loc_or_input_loc (cond), diff --git a/gcc/testsuite/g++.dg/warn/Wparentheses-31.C b/gcc/testsuite/g++.dg/warn/Wparentheses-31.C new file mode 100644 index 00000000000..f29234ce589 --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/Wparentheses-31.C @@ -0,0 +1,59 @@ +/* Test that -Wparentheses warns for struct/class assignments, + except for explicit calls to operator= (). */ +/* PR c++/25689 */ +/* { dg-options "-Wparentheses" } */ + +struct A +{ + A& operator= (int); + A operator= (double); + operator bool (); +}; + +struct B +{ + bool x; + B& operator= (int); + B operator= (double); + operator bool (); +}; + +struct C +{ + C& operator= (int); + virtual C operator= (double); + operator bool (); +}; + +/* Test empty class */ +void f1 (A a1, A a2) +{ + if (a1 = 0); /* { dg-warning "suggest parentheses" } */ + if (a1 = 0.); /* { dg-warning "suggest parentheses" } */ + if (a1.operator= (0)); + if (a1.operator= (a2)); + + /* Ideally, we'd warn for empty classes using trivial operator= (below), + but we don't do so yet as it is a non-trivial COMPOUND_EXPR. */ + if (a1 = a2); /* { dg-warning "suggest parentheses" "" { xfail *-*-* } } */ +} + +/* Test non-empty class */ +void f2 (B b1, B b2) +{ + if (b1 = 0); /* { dg-warning "suggest parentheses" } */ + if (b1 = 0.); /* { dg-warning "suggest parentheses" } */ + if (b1 = b2); /* { dg-warning "suggest parentheses" } */ + if (b1.operator= (0)); + if (b1.operator= (b2)); +} + +/* Test class with vtable */ +void f3 (C c1, C c2) +{ + if (c1 = 0); /* { dg-warning "suggest parentheses" } */ + if (c1 = 0.); /* { dg-warning "suggest parentheses" } */ + if (c1 = c2); /* { dg-warning "suggest parentheses" } */ + if (c1.operator= (0)); + if (c1.operator= (c2)); +}
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