This PR complains that we issue a -Wconversion warning in
template <int N> struct X {};
template <class T> X<sizeof(T)> foo();
saying "conversion from 'long unsigned int' to 'int' may change value".
While it's not technically wrong, I suspect -Wconversion warnings aren't
all that useful for value-dependent expressions. So this patch disables
them, though I'm open to other ideas. This is a regression that started
with r241425:
@@ -7278,7 +7306,7 @@ convert_template_argument (tree parm,
val = error_mark_node;
}
}
- else if (!dependent_template_arg_p (orig_arg)
+ else if (!type_dependent_expression_p (orig_arg)
&& !uses_template_parms (t))
/* We used to call digest_init here. However, digest_init
will report errors, which we don't want when complain
Here orig_arg is SIZEOF_EXPR<T>, dependent_template_arg_p (orig_arg) was
true, but type_dependent_expression_p (orig_arg) is false so we warn in
convert_nontype_argument.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10?
gcc/cp/ChangeLog:
PR c++/99331
* cvt.c (cp_convert_and_check): Don't emit -Wconversion warnings
when the expression is value-dependent.
gcc/testsuite/ChangeLog:
PR c++/99331
* g++.dg/warn/Wconversion5.C: New test.
---
gcc/cp/cvt.c | 7 ++++++-
gcc/testsuite/g++.dg/warn/Wconversion5.C | 14 ++++++++++++++
2 files changed, 20 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wconversion5.C
diff --git a/gcc/cp/cvt.c b/gcc/cp/cvt.c
index 2ea32101f07..55024b2b966 100644
--- a/gcc/cp/cvt.c
+++ b/gcc/cp/cvt.c
@@ -663,7 +663,12 @@ cp_convert_and_check (tree type, tree expr, tsubst_flags_t
complain)
result = cp_convert (type, expr, complain);
if ((complain & tf_warning)
- && c_inhibit_evaluation_warnings == 0)
+ && c_inhibit_evaluation_warnings == 0
+ /* Issuing conversion warnings for value-dependent expressions is
+ likely too noisy. */
+ && !(processing_template_decl
+ && potential_constant_expression (expr)
+ && value_dependent_expression_p (expr)))
{
tree folded = cp_fully_fold (expr);
tree folded_result;
diff --git a/gcc/testsuite/g++.dg/warn/Wconversion5.C
b/gcc/testsuite/g++.dg/warn/Wconversion5.C
new file mode 100644
index 00000000000..47106a7c2fa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wconversion5.C
@@ -0,0 +1,14 @@
+// PR c++/99331
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wconversion" }
+// Don't issue -Wconversion warnings for value-dependent expressions.
+
+template <int N> struct X {};
+template <class T> X<sizeof(T)> foo();
+template <class T> X<alignof(T)> foo2();
+
+template <typename T>
+struct S {
+ using t = X<sizeof(T)>;
+ using u = X<alignof(T)>;
+};
base-commit: 0d737ed2171165ba39ab5647f8a94c588fc9a898
--
2.29.2
