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* [gcc r13-23] c++: Add diagnostic when operator= is used as truth cond [PR25689]
@ 2022-04-29 2:59 Jason Merrill
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From: Jason Merrill @ 2022-04-29 2:59 UTC (permalink / raw)
To: gcc-cvs
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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