Implementation is pretty straightforward. The only catch is that the
middle-end doesn't actually assume that REFERENCE_TYPEs are non-NULL so
code like
int &a = *(int *)0;
if (&a != 0)
will warn that &a will never be NULL yet the middle-end will fold the
conditional to false instead of true anyway. But I guess that's not a
big deal.
Does this look OK after testing?
gcc/c-family/ChangeLog:
* c-common.c (c_common_truthvalue_conversion): Warn when
converting an address of a reference to a truth value.
gcc/cp/ChangeLog:
* typeck.c (cp_build_binary_op): Warn when comparing an address
of a reference against NULL.
gcc/testsuite/ChangeLog:
g++.dg/warn/Walways-true-3.C: New test.
---
gcc/c-family/c-common.c | 12 ++++++++++++
gcc/cp/typeck.c | 10 ++++++++--
gcc/testsuite/g++.dg/warn/Walways-true-3.C | 30 ++++++++++++++++++++++++++++++
3 files changed, 50 insertions(+), 2 deletions(-)
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 7fe7fa6..89bbdc9 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -4784,6 +4784,18 @@ 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 = TREE_OPERAND (expr, 0);
+ if (decl_with_nonnull_addr_p (inner))
+ warning_at (location,
+ OPT_Waddress,
+ "the address of reference %qD may be assumed to "
+ "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 250b5d6..0d177b7 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -4415,7 +4415,10 @@ cp_build_binary_op (location_t location,
else
result_type = type0;
- if (TREE_CODE (op0) == ADDR_EXPR
+ if ((TREE_CODE (op0) == ADDR_EXPR
+ || (CONVERT_EXPR_P (op0)
+ && TREE_CODE (TREE_TYPE (TREE_OPERAND (op0, 0)))
+ == REFERENCE_TYPE))
&& decl_with_nonnull_addr_p (TREE_OPERAND (op0, 0)))
{
if ((complain & tf_warning)
@@ -4437,7 +4440,10 @@ cp_build_binary_op (location_t location,
else
result_type = type1;
- if (TREE_CODE (op1) == ADDR_EXPR
+ if ((TREE_CODE (op1) == ADDR_EXPR
+ || (CONVERT_EXPR_P (op1)
+ && TREE_CODE (TREE_TYPE (TREE_OPERAND (op1, 0)))
+ == REFERENCE_TYPE))
&& decl_with_nonnull_addr_p (TREE_OPERAND (op1, 0)))
{
if ((complain & tf_warning)
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..a145932
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Walways-true-3.C
@@ -0,0 +1,30 @@
+// { dg-options "-Waddress" }
+
+void foo (void);
+
+int d;
+int &c = d;
+
+void
+bar (int &a)
+{
+ int &b = a;
+
+ if (&a) // { dg-warning "address of reference" }
+ foo ();
+
+ if (&b) // { dg-warning "address of reference" }
+ foo ();
+
+ if (&c) // { dg-warning "address of reference" }
+ foo ();
+
+ if (&a == 0) // { dg-warning "never be NULL" }
+ foo ();
+
+ if (&b != 0) // { dg-warning "never be NULL" }
+ foo ();
+
+ if (0 == &c) // { dg-warning "never be NULL" }
+ foo ();
+}
--
2.4.0.rc2.31.g7c597ef
