[gcc r11-7458] PR c++/99251 - inconsistent -Wnonnull warning behaviour with dynamic_cast
Martin Sebor
msebor@gcc.gnu.org
Tue Mar 2 18:17:33 GMT 2021
https://gcc.gnu.org/g:66ecb059c9d77cfcfb06cbdc3cac6a63b9e67f3d
commit r11-7458-g66ecb059c9d77cfcfb06cbdc3cac6a63b9e67f3d
Author: Martin Sebor <msebor@redhat.com>
Date: Tue Mar 2 11:12:50 2021 -0700
PR c++/99251 - inconsistent -Wnonnull warning behaviour with dynamic_cast
gcc/cp/ChangeLog:
PR c++/99251
* class.c (build_base_path): Call build_if_nonnull.
* cp-tree.h (build_if_nonnull): Declare.
* rtti.c (ifnonnull): Rename...
(build_if_nonnull): ...to this. Set no-warning bit on COND_EXPR.
(build_dynamic_cast_1): Adjust to name change.
gcc/testsuite/ChangeLog:
PR c++/99251
* g++.dg/warn/Wnonnull9.C: Expect no warnings.
* g++.dg/warn/Wnonnull12.C: New test.
Diff:
---
gcc/cp/class.c | 21 ++++-----------------
gcc/cp/cp-tree.h | 1 +
gcc/cp/rtti.c | 24 +++++++++++++++---------
gcc/testsuite/g++.dg/warn/Wnonnull12.C | 29 +++++++++++++++++++++++++++++
gcc/testsuite/g++.dg/warn/Wnonnull9.C | 20 ++++++++++++++------
5 files changed, 63 insertions(+), 32 deletions(-)
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index ea007e88e6e..856e81e3d1a 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -402,16 +402,9 @@ build_base_path (enum tree_code code,
if (TREE_SIDE_EFFECTS (expr) && (null_test || virtual_access))
expr = save_expr (expr);
- /* Now that we've saved expr, build the real null test. */
+ /* Store EXPR and build the real null test just before returning. */
if (null_test)
- {
- tree zero = cp_convert (TREE_TYPE (expr), nullptr_node, complain);
- null_test = build2_loc (input_location, NE_EXPR, boolean_type_node,
- expr, zero);
- /* This is a compiler generated comparison, don't emit
- e.g. -Wnonnull-compare warning for it. */
- TREE_NO_WARNING (null_test) = 1;
- }
+ null_test = expr;
/* If this is a simple base reference, express it as a COMPONENT_REF. */
if (code == PLUS_EXPR && !virtual_access
@@ -516,14 +509,8 @@ build_base_path (enum tree_code code,
out:
if (null_test)
- {
- expr = fold_build3_loc (input_location, COND_EXPR, target_type, null_test,
- expr, build_zero_cst (target_type));
- /* Avoid warning for the whole conditional expression (in addition
- to NULL_TEST itself -- see above) in case the result is used in
- a nonnull context that the front end -Wnonnull checks. */
- TREE_NO_WARNING (expr) = 1;
- }
+ /* Wrap EXPR in a null test. */
+ expr = build_if_nonnull (null_test, expr, complain);
return expr;
}
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 544e99538a4..b4728c87d0b 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7279,6 +7279,7 @@ extern void emit_support_tinfos (void);
extern bool emit_tinfo_decl (tree);
extern unsigned get_pseudo_tinfo_index (tree);
extern tree get_pseudo_tinfo_type (unsigned);
+extern tree build_if_nonnull (tree, tree, tsubst_flags_t);
/* in search.c */
extern tree get_parent_with_private_access (tree decl, tree binfo);
diff --git a/gcc/cp/rtti.c b/gcc/cp/rtti.c
index b41d95469c6..5a33b83afd0 100644
--- a/gcc/cp/rtti.c
+++ b/gcc/cp/rtti.c
@@ -121,7 +121,6 @@ vec<tree, va_gc> *unemitted_tinfo_decls;
and are generated as needed. */
static GTY (()) vec<tinfo_s, va_gc> *tinfo_descs;
-static tree ifnonnull (tree, tree, tsubst_flags_t);
static tree tinfo_name (tree, bool);
static tree build_dynamic_cast_1 (location_t, tree, tree, tsubst_flags_t);
static tree throw_bad_cast (void);
@@ -529,16 +528,23 @@ get_typeid (tree type, tsubst_flags_t complain)
/* Check whether TEST is null before returning RESULT. If TEST is used in
RESULT, it must have previously had a save_expr applied to it. */
-static tree
-ifnonnull (tree test, tree result, tsubst_flags_t complain)
+tree
+build_if_nonnull (tree test, tree result, tsubst_flags_t complain)
{
- tree cond = build2 (NE_EXPR, boolean_type_node, test,
- cp_convert (TREE_TYPE (test), nullptr_node, complain));
+ tree null_ptr = cp_convert (TREE_TYPE (test), nullptr_node, complain);
+ tree cond = build2 (NE_EXPR, boolean_type_node, test, null_ptr);
+
/* This is a compiler generated comparison, don't emit
e.g. -Wnonnull-compare warning for it. */
TREE_NO_WARNING (cond) = 1;
- return build3 (COND_EXPR, TREE_TYPE (result), cond, result,
- cp_convert (TREE_TYPE (result), nullptr_node, complain));
+
+ null_ptr = cp_convert (TREE_TYPE (result), nullptr_node, complain);
+ cond = build3 (COND_EXPR, TREE_TYPE (result), cond, result, null_ptr);
+
+ /* Likewise, don't emit -Wnonnull for using the result to call
+ a member function. */
+ TREE_NO_WARNING (cond) = 1;
+ return cond;
}
/* Execute a dynamic cast, as described in section 5.2.6 of the 9/93 working
@@ -671,7 +677,7 @@ build_dynamic_cast_1 (location_t loc, tree type, tree expr,
expr1 = build_headof (expr);
if (TREE_TYPE (expr1) != type)
expr1 = build1 (NOP_EXPR, type, expr1);
- return ifnonnull (expr, expr1, complain);
+ return build_if_nonnull (expr, expr1, complain);
}
else
{
@@ -786,7 +792,7 @@ build_dynamic_cast_1 (location_t loc, tree type, tree expr,
/* Now back to the type we want from a void*. */
result = cp_convert (type, result, complain);
- return ifnonnull (expr, result, complain);
+ return build_if_nonnull (expr, result, complain);
}
}
else
diff --git a/gcc/testsuite/g++.dg/warn/Wnonnull12.C b/gcc/testsuite/g++.dg/warn/Wnonnull12.C
new file mode 100644
index 00000000000..7b2606302f5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wnonnull12.C
@@ -0,0 +1,29 @@
+/* PR c++/99251 - inconsistent -Wnonnull warning behaviour with dynamic_cast
+ { dg-do compile }
+ { dg-options "-Wall" } */
+
+struct A
+{
+ virtual ~A ();
+};
+
+struct B: A
+{
+ int f (int);
+};
+
+int f1 (A *p)
+{
+ if (!p)
+ return 0;
+
+ return (dynamic_cast<B *>(p))->f (1);
+}
+
+int f2 (A *p)
+{
+ if (!p)
+ return 0;
+
+ return dynamic_cast<B *>(p)->f (2); // { dg-bogus "\\\[-Wnonnull" }
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wnonnull9.C b/gcc/testsuite/g++.dg/warn/Wnonnull9.C
index b6135c4a624..88bf55adba2 100644
--- a/gcc/testsuite/g++.dg/warn/Wnonnull9.C
+++ b/gcc/testsuite/g++.dg/warn/Wnonnull9.C
@@ -38,13 +38,17 @@ void static_cast_const_C_ptr (B *p)
void dynamic_cast_C_ptr (B *p)
{
- // The dynamic_cast might fail so a warning is justified.
- dynamic_cast<C*>(p->bptr ())->g (); // { dg-warning "\\\[-Wnonnull" }
+ /* Unlike static_cast, dynamic cast may return null even for a nonnull
+ operand but detecting assumptions to the contrary isn't -Wnonnull's
+ purpose. Verify -Wnonnull isn't issued, either for the implicitly
+ emitted null check or for other reasons (the latter may be worth
+ warning for by some other warning). See also pr99251. */
+ dynamic_cast<C*>(p->bptr ())->g (); // { dg-bogus "\\\[-Wnonnull" }
}
void dynamic_cast_const_C_ptr (B *p)
{
- dynamic_cast<const C*>(p->bptr ())->g (); // { dg-warning "\\\[-Wnonnull" }
+ dynamic_cast<const C*>(p->bptr ())->g (); // { dg-bogus "\\\[-Wnonnull" }
}
@@ -107,11 +111,15 @@ void static_cast_const_D_ptr (B *p)
void dynamic_cast_D_ptr (B *p)
{
- // The dynamic_cast might fail so a warning is justified.
- dynamic_cast<D*>(p->bptr ())->g (); // { dg-warning "\\\[-Wnonnull" }
+ /* Unlike static_cast, dynamic cast may return null even for a nonnull
+ operand but detecting assumptions to the contrary isn't -Wnonnull's
+ purpose. Verify -Wnonnull isn't issued, either for the implicitly
+ emitted null check or for other reasons (the latter may be worth
+ warning for by some other warning). See also pr99251. */
+ dynamic_cast<D*>(p->bptr ())->g (); // { dg-bogus "\\\[-Wnonnull" }
}
void dynamic_cast_const_D_ptr (B *p)
{
- dynamic_cast<const D*>(p->bptr ())->g (); // { dg-warning "\\\[-Wnonnull" }
+ dynamic_cast<const D*>(p->bptr ())->g (); // { dg-bogus "\\\[-Wnonnull" }
}
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