* [committed] libstdc++: Fix visit<void>(v) for non-void visitors [PR106589]
@ 2022-08-23 15:39 Jonathan Wakely
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From: Jonathan Wakely @ 2022-08-23 15:39 UTC (permalink / raw)
To: libstdc++, gcc-patches
Tested powerpc64le-linux, pushed to trunk. Backport to gcc-12 needed.
-- >8 --
The optimization for the common case of std::visit forgot to handle the
edge case of passing zero variants to a non-void visitor and converting
the result to void.
libstdc++-v3/ChangeLog:
PR libstdc++/106589
* include/std/variant (__do_visit): Handle is_void<R> for zero
argument case.
* testsuite/20_util/variant/visit_r.cc: Check std::visit<void>(v).
---
libstdc++-v3/include/std/variant | 7 ++++++-
libstdc++-v3/testsuite/20_util/variant/visit_r.cc | 8 ++++++++
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index f8f15665433..c234b54421e 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1728,7 +1728,12 @@ namespace __variant
{
// Get the silly case of visiting no variants out of the way first.
if constexpr (sizeof...(_Variants) == 0)
- return std::forward<_Visitor>(__visitor)();
+ {
+ if constexpr (is_void_v<_Result_type>)
+ return (void) std::forward<_Visitor>(__visitor)();
+ else
+ return std::forward<_Visitor>(__visitor)();
+ }
else
{
constexpr size_t __max = 11; // "These go to eleven."
diff --git a/libstdc++-v3/testsuite/20_util/variant/visit_r.cc b/libstdc++-v3/testsuite/20_util/variant/visit_r.cc
index 712459f25e3..c77b259c386 100644
--- a/libstdc++-v3/testsuite/20_util/variant/visit_r.cc
+++ b/libstdc++-v3/testsuite/20_util/variant/visit_r.cc
@@ -54,10 +54,18 @@ void test02()
std::visit<const void>(Visitor(), v);
}
+void test03()
+{
+ // PR libstdc++/106589 - visit<void> rejects lambdas that do not return void
+ auto visitor = []{ return 0; };
+ std::visit<void>(visitor);
+ std::visit<void>(static_cast<int(*)()>(visitor));
+}
int
main()
{
test01();
test02();
+ test03();
}
--
2.37.2
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