This patch fixes a pretty stoopid thinko. When I added code to warn
about pessimizing std::move in initializations like
T t{std::move(T())};
I also added code to unwrap the expression from { }. But when we have
return {std::move(t)};
we cannot warn about a redundant std::move because the implicit move
wouldn't happen for "return {t};" because the expression isn't just
a name. However, we still want to warn about
return {std::move(T())};
so let's not disable the -Wpessimizing-move warning. Tests added for
both cases.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
gcc/cp/ChangeLog:
* typeck.cc (maybe_warn_pessimizing_move): Don't warn about
redundant std::move when the expression was wrapped in { }.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/Wpessimizing-move10.C: New test.
* g++.dg/cpp0x/Wredundant-move12.C: New test.
---
gcc/cp/typeck.cc | 13 +++++--
.../g++.dg/cpp0x/Wpessimizing-move10.C | 30 ++++++++++++++++
.../g++.dg/cpp0x/Wredundant-move12.C | 36 +++++++++++++++++++
3 files changed, 77 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/Wpessimizing-move10.C
create mode 100644 gcc/testsuite/g++.dg/cpp0x/Wredundant-move12.C
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 992ebfd99fb..7fde65adaa4 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -10397,11 +10397,15 @@ maybe_warn_pessimizing_move (tree expr, tree type,
bool return_p)
if (!CLASS_TYPE_P (type))
return;
+ bool wrapped_p = false;
/* A a = std::move (A()); */
if (TREE_CODE (expr) == TREE_LIST)
{
if (list_length (expr) == 1)
- expr = TREE_VALUE (expr);
+ {
+ expr = TREE_VALUE (expr);
+ wrapped_p = true;
+ }
else
return;
}
@@ -10410,7 +10414,10 @@ maybe_warn_pessimizing_move (tree expr, tree type,
bool return_p)
else if (TREE_CODE (expr) == CONSTRUCTOR)
{
if (CONSTRUCTOR_NELTS (expr) == 1)
- expr = CONSTRUCTOR_ELT (expr, 0)->value;
+ {
+ expr = CONSTRUCTOR_ELT (expr, 0)->value;
+ wrapped_p = true;
+ }
else
return;
}
@@ -10458,6 +10465,8 @@ maybe_warn_pessimizing_move (tree expr, tree type, bool
return_p)
/* Warn if the move is redundant. It is redundant when we would
do maybe-rvalue overload resolution even without std::move. */
else if (warn_redundant_move
+ /* This doesn't apply for return {std::move (t)};. */
+ && !wrapped_p
&& !warning_suppressed_p (expr, OPT_Wredundant_move)
&& (moved = treat_lvalue_as_rvalue_p (arg, /*return*/true)))
{
diff --git a/gcc/testsuite/g++.dg/cpp0x/Wpessimizing-move10.C
b/gcc/testsuite/g++.dg/cpp0x/Wpessimizing-move10.C
new file mode 100644
index 00000000000..77314141da3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/Wpessimizing-move10.C
@@ -0,0 +1,30 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wpessimizing-move" }
+
+// Define std::move.
+namespace std {
+ template<typename _Tp>
+ struct remove_reference
+ { typedef _Tp type; };
+
+ template<typename _Tp>
+ struct remove_reference<_Tp&>
+ { typedef _Tp type; };
+
+ template<typename _Tp>
+ struct remove_reference<_Tp&&>
+ { typedef _Tp type; };
+
+ template<typename _Tp>
+ constexpr typename std::remove_reference<_Tp>::type&&
+ move(_Tp&& __t) noexcept
+ { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
+}
+
+struct S { };
+
+S
+f ()
+{
+ return {std::move(S())}; // { dg-warning "moving a temporary object
prevents copy elision" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp0x/Wredundant-move12.C
b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move12.C
new file mode 100644
index 00000000000..192d981ba5e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move12.C
@@ -0,0 +1,36 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wredundant-move" }
+
+// Define std::move.
+namespace std {
+ template<typename _Tp>
+ struct remove_reference
+ { typedef _Tp type; };
+
+ template<typename _Tp>
+ struct remove_reference<_Tp&>
+ { typedef _Tp type; };
+
+ template<typename _Tp>
+ struct remove_reference<_Tp&&>
+ { typedef _Tp type; };
+
+ template<typename _Tp>
+ constexpr typename std::remove_reference<_Tp>::type&&
+ move(_Tp&& __t) noexcept
+ { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
+}
+
+struct S1 {
+ S1();
+ S1(S1 const &) = delete;
+ S1(S1 &&);
+ S1 operator =(S1 const &) = delete;
+ S1 operator =(S1 &&);
+};
+
+struct S2 { S2(S1); };
+S2 f() {
+ S1 s;
+ return { std::move(s) }; // { dg-bogus "redundant move" }
+}
base-commit: cc4fa7a210b638d6a46f14dab17f2361389d18e1
--
2.37.2
