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C++ PATCH for c++/87519 - bogus warning with -Wsign-conversion
- From: Marek Polacek <polacek at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>, Jason Merrill <jason at redhat dot com>
- Date: Thu, 8 Aug 2019 10:50:00 -0400
- Subject: C++ PATCH for c++/87519 - bogus warning with -Wsign-conversion
This PR complains about bogus -Wsign-conversion warning even with an
explicit cast, which the documentation says should suppress the warning.
Pretty similar to c++/86190 which I fixed here
<https://gcc.gnu.org/ml/gcc-patches/2018-07/msg00115.html>.
The problem only happens when using a typedef, because in cp_build_binary_op
we're comparing the types using ==, which I think only works for canonical
types. So use same_type_p to avoid this problem.
Bootstrapped/regtested on x86_64-linux, ok for trunk? I think it makes sense
to fix in in 9.3 too.
2019-08-08 Marek Polacek <polacek@redhat.com>
PR c++/87519 - bogus warning with -Wsign-conversion.
* typeck.c (cp_build_binary_op): Use same_type_p instead of comparing
the types directly.
* g++.dg/warn/Wsign-conversion-5.C: New test.
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index 7e4ea3bee75..4cc0ee0128d 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -5509,9 +5509,9 @@ cp_build_binary_op (const op_location_t &location,
if (! converted)
{
warning_sentinel w (warn_sign_conversion, short_compare);
- if (TREE_TYPE (op0) != result_type)
+ if (!same_type_p (TREE_TYPE (op0), result_type))
op0 = cp_convert_and_check (result_type, op0, complain);
- if (TREE_TYPE (op1) != result_type)
+ if (!same_type_p (TREE_TYPE (op1), result_type))
op1 = cp_convert_and_check (result_type, op1, complain);
if (op0 == error_mark_node || op1 == error_mark_node)
diff --git gcc/testsuite/g++.dg/warn/Wsign-conversion-5.C gcc/testsuite/g++.dg/warn/Wsign-conversion-5.C
new file mode 100644
index 00000000000..ff384164901
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/Wsign-conversion-5.C
@@ -0,0 +1,18 @@
+// PR c++/87519 - bogus warning with -Wsign-conversion.
+// { dg-options "-Wsign-conversion" }
+
+typedef unsigned long int uint64_t;
+
+void f(unsigned long int a, int q)
+{
+ a += a + q; // { dg-warning "may change the sign" }
+
+ // Explicit cast should disable the warning.
+ a = a + static_cast<uint64_t>(q);
+ a = a + (uint64_t) q;
+ a = a + uint64_t(q);
+ a = a + static_cast<const uint64_t>(q);
+ a = a + (const uint64_t) q;
+ a = a + static_cast<unsigned long int>(q);
+ a = a + static_cast<const unsigned long int>(q);
+}