Here is an updated version of the patch with, hopefully, all your
suggestions made. I decided to add calls to STRIP_NOPS before emitting
the warning so that we properly warn for cases where there's a cast in
between the whole thing, e.g.
if (!&(int &)a)
I also added guards to emit the warnings only when the stripped operand
is actually a decl so that we don't pass a non-decl argument to
warning_at() which can happen in a case like
if (!&(int &)*(int *)0)
Does this look OK now after testing?
gcc/c-family/ChangeLog:
PR c++/65168
* c-common.c (c_common_truthvalue_conversion): Warn when
converting an address of a reference to a truth value.
gcc/cp/ChangeLog:
PR c++/65168
* typeck.c (cp_build_binary_op): Warn when comparing an address
of a reference against NULL.
gcc/testsuite/ChangeLog:
PR c++/65168
g++.dg/warn/Walways-true-3.C: New test.
---
gcc/c-family/c-common.c | 14 ++++++++++
gcc/cp/typeck.c | 34 ++++++++++++++++++++++
gcc/testsuite/g++.dg/warn/Walways-true-3.C | 45 ++++++++++++++++++++++++++++++
3 files changed, 93 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/warn/Walways-true-3.C
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 9797e17..c353c72 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -4806,6 +4806,20 @@ c_common_truthvalue_conversion (location_t location,
tree expr)
tree totype = TREE_TYPE (expr);
tree fromtype = TREE_TYPE (TREE_OPERAND (expr, 0));
+ if (POINTER_TYPE_P (totype)
+ && TREE_CODE (fromtype) == REFERENCE_TYPE)
+ {
+ tree inner = expr;
+ STRIP_NOPS (inner);
+
+ if (DECL_P (inner))
+ warning_at (location,
+ OPT_Waddress,
+ "the compiler can assume that the address of "
+ "%qD will always evaluate to %<true%>",
+ inner);
+ }
+
/* Don't cancel the effect of a CONVERT_EXPR from a REFERENCE_TYPE,
since that affects how `default_conversion' will behave. */
if (TREE_CODE (totype) == REFERENCE_TYPE
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 91db32a..13fb401 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -4423,6 +4423,23 @@ cp_build_binary_op (location_t location,
warning (OPT_Waddress, "the address of %qD will never be NULL",
TREE_OPERAND (op0, 0));
}
+
+ if (CONVERT_EXPR_P (op0)
+ && TREE_CODE (TREE_TYPE (TREE_OPERAND (op0, 0)))
+ == REFERENCE_TYPE)
+ {
+ tree inner_op0 = op0;
+ STRIP_NOPS (inner_op0);
+
+ if ((complain & tf_warning)
+ && c_inhibit_evaluation_warnings == 0
+ && !TREE_NO_WARNING (op0)
+ && DECL_P (inner_op0))
+ warning (OPT_Waddress,
+ "the compiler can assume that the address of "
+ "%qD will never be NULL",
+ inner_op0);
+ }
}
else if (((code1 == POINTER_TYPE || TYPE_PTRDATAMEM_P (type1))
&& null_ptr_cst_p (op0))
@@ -4445,6 +4462,23 @@ cp_build_binary_op (location_t location,
warning (OPT_Waddress, "the address of %qD will never be NULL",
TREE_OPERAND (op1, 0));
}
+
+ if (CONVERT_EXPR_P (op1)
+ && TREE_CODE (TREE_TYPE (TREE_OPERAND (op1, 0)))
+ == REFERENCE_TYPE)
+ {
+ tree inner_op1 = op1;
+ STRIP_NOPS (inner_op1);
+
+ if ((complain & tf_warning)
+ && c_inhibit_evaluation_warnings == 0
+ && !TREE_NO_WARNING (op1)
+ && DECL_P (inner_op1))
+ warning (OPT_Waddress,
+ "the compiler can assume that the address of "
+ "%qD will never be NULL",
+ inner_op1);
+ }
}
else if ((code0 == POINTER_TYPE && code1 == POINTER_TYPE)
|| (TYPE_PTRDATAMEM_P (type0) && TYPE_PTRDATAMEM_P (type1)))
diff --git a/gcc/testsuite/g++.dg/warn/Walways-true-3.C
b/gcc/testsuite/g++.dg/warn/Walways-true-3.C
new file mode 100644
index 0000000..0d13d3f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Walways-true-3.C
@@ -0,0 +1,45 @@
+// { dg-options "-Waddress" }
+
+void foo (void);
+
+int d;
+int &c = d;
+
+void
+bar (int &a)
+{
+ int &b = a;
+
+ if ((int *)&a) // { dg-warning "address of" }
+ foo ();
+
+ if (&b) // { dg-warning "address of" }
+ foo ();
+
+ if (!&c) // { dg-warning "address of" }
+ foo ();
+
+ if (!&(int &)(int &)a) // { dg-warning "address of" }
+ foo ();
+
+ if (&a == 0) // { dg-warning "never be NULL" }
+ foo ();
+
+ if (&b != 0) // { dg-warning "never be NULL" }
+ foo ();
+
+ if (0 == &(int &)(int &)c) // { dg-warning "never be NULL" }
+ foo ();
+
+ if (&a != (int *)0) // { dg-warning "never be NULL" }
+ foo ();
+}
+
+bool
+bar_1 (int &a)
+{
+ if (d == 5)
+ return &a; // { dg-warning "address of" }
+ else
+ return !&(int &)(int &)a; // { dg-warning "address of" }
+}
--
2.4.0.rc2.31.g7c597ef
