On Wed, Dec 01, 2021 at 11:16:27PM -0500, Jason Merrill wrote:
On 12/1/21 10:16, Marek Polacek wrote:
In r11-4758, I tried to fix this problem:
int &&i = 0;
decltype(auto) j = i; // should behave like int &&j = i; error
wherein do_auto_deduction was getting confused with a REFERENCE_REF_P
and it didn't realize its operand was a name, not an expression, and
deduced the wrong type.
Unfortunately that fix broke this:
int&& r = 1;
decltype(auto) rr = (r);
where 'rr' should be 'int &' since '(r)' is an expression, not a name. But
because I stripped the INDIRECT_REF with the r11-4758 change, we deduced
'rr's type as if decltype had gotten a name, resulting in 'int &&'.
I suspect I thought that the REF_PARENTHESIZED_P check when setting
'bool id' in do_auto_deduction would handle the (r) case, but that's not
the case; while the documentation for REF_PARENTHESIZED_P specifically says
it can be set in INDIRECT_REF, we don't actually do so.
This patch sets REF_PARENTHESIZED_P even on REFERENCE_REF_P, so that
do_auto_deduction can use it.
It also removes code in maybe_undo_parenthesized_ref that I think is
dead -- and we don't hit it while running dg.exp. To adduce more data,
it also looks dead here:
https://splichal.eu/lcov/gcc/cp/semantics.c.gcov.html
Agreed, that code is dead since r9-1417.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk and 11?
PR c++/103403
gcc/cp/ChangeLog:
* cp-gimplify.c (cp_fold): Don't recurse if maybe_undo_parenthesized_ref
doesn't change its argument.
* pt.c (do_auto_deduction): Don't strip REFERENCE_REF_P trees. Also
REF_PARENTHESIZED_P for REFERENCE_REF_P.
* semantics.c (force_paren_expr): Set REF_PARENTHESIZED_P on
REFERENCE_REF_P trees too.
(maybe_undo_parenthesized_ref): Remove dead code.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/decltype-auto2.C: New test.
* g++.dg/cpp1y/decltype-auto3.C: New test.
---
gcc/cp/cp-gimplify.c | 3 ++-
gcc/cp/pt.c | 5 ++---
gcc/cp/semantics.c | 18 ++++--------------
gcc/testsuite/g++.dg/cpp1y/decltype-auto2.C | 12 ++++++++++++
gcc/testsuite/g++.dg/cpp1y/decltype-auto3.C | 12 ++++++++++++
5 files changed, 32 insertions(+), 18 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto2.C
create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto3.C
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index 0a002db14e7..e3ede02a48e 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -2421,7 +2421,8 @@ cp_fold (tree x)
if (REF_PARENTHESIZED_P (x))
{
tree p = maybe_undo_parenthesized_ref (x);
- return cp_fold (p);
+ if (p != x)
+ return cp_fold (p);
}
goto unary;
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index f4b9d9673fb..c5b41b57028 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -29889,11 +29889,10 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
else if (AUTO_IS_DECLTYPE (auto_node))
{
tree stripped_init = tree_strip_any_location_wrapper (init);
- if (REFERENCE_REF_P (stripped_init))
- stripped_init = TREE_OPERAND (stripped_init, 0);
bool id = (DECL_P (stripped_init)
|| ((TREE_CODE (init) == COMPONENT_REF
- || TREE_CODE (init) == SCOPE_REF)
+ || TREE_CODE (init) == SCOPE_REF
+ || REFERENCE_REF_P (init))
&& !REF_PARENTHESIZED_P (init)));
This change seems wrong; not all references are id-expressions or member
accesses. For instance, a call to a function returning a reference is not.
I think we still want to depend on the TREE_CODE, but we need to look at the
TREE_CODE of stripped_init, not init.
Yes indeed, id was wrong. I didn't notice because we still deduced to the
right type!
This version only strips REFERENCE_REF_P when they aren't REF_PARENTHESIZED_P,
so that, as the comment says, I can tell '(r)' and 'r' apart. Since we can
deduce the correct type even with the wrong id, I tested this by using the
two functions in decltype-auto4.C, and adding gcc_assert(id) or !id so that
I can verify that id looks correct with this patch.
Also add a new test case: decltype-auto4.C. It would still be nice to test
more; I'm not sure how well we test [dcl.type.decltype]/1.1 and /1.2. I'm
also adding decomp-decltype1.C, which fixes decltype + structured binding.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk / 11?
-- >8 --
In r11-4758, I tried to fix this problem:
int &&i = 0;
decltype(auto) j = i; // should behave like int &&j = i; error
wherein do_auto_deduction was getting confused with a REFERENCE_REF_P
and it didn't realize its operand was a name, not an expression, and
deduced the wrong type.
Unfortunately that fix broke this:
int&& r = 1;
decltype(auto) rr = (r);
where 'rr' should be 'int &' since '(r)' is an expression, not a name. But
because I stripped the INDIRECT_REF with the r11-4758 change, we deduced
'rr's type as if decltype had gotten a name, resulting in 'int &&'.
I suspect I thought that the REF_PARENTHESIZED_P check when setting
'bool id' in do_auto_deduction would handle the (r) case, but that's not
the case; while the documentation for REF_PARENTHESIZED_P specifically says
it can be set in INDIRECT_REF, we don't actually do so.
This patch sets REF_PARENTHESIZED_P even on REFERENCE_REF_P, so that
do_auto_deduction can use it.
It also removes code in maybe_undo_parenthesized_ref that I think is
dead -- and we don't hit it while running dg.exp. To adduce more data,
it also looks dead here:
https://splichal.eu/lcov/gcc/cp/semantics.c.gcov.html
(It's dead since r9-1417.)
Also add a fixed test for c++/81176.
PR c++/103403
gcc/cp/ChangeLog:
* cp-gimplify.c (cp_fold): Don't recurse if maybe_undo_parenthesized_ref
doesn't change its argument.
* pt.c (do_auto_deduction): Don't strip REFERENCE_REF_P trees if they
are REF_PARENTHESIZED_P. Use stripped_init when checking for
id-expression.
* semantics.c (force_paren_expr): Set REF_PARENTHESIZED_P on
REFERENCE_REF_P trees too.
(maybe_undo_parenthesized_ref): Remove dead code.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/decltype-auto2.C: New test.
* g++.dg/cpp1y/decltype-auto3.C: New test.
* g++.dg/cpp1y/decltype-auto4.C: New test.
* g++.dg/cpp1z/decomp-decltype1.C: New test.
---
gcc/cp/cp-gimplify.c | 3 +-
gcc/cp/pt.c | 15 +++--
gcc/cp/semantics.c | 18 ++---
gcc/testsuite/g++.dg/cpp1y/decltype-auto2.C | 12 ++++
gcc/testsuite/g++.dg/cpp1y/decltype-auto3.C | 12 ++++
gcc/testsuite/g++.dg/cpp1y/decltype-auto4.C | 65 +++++++++++++++++++
gcc/testsuite/g++.dg/cpp1z/decomp-decltype1.C | 28 ++++++++
7 files changed, 133 insertions(+), 20 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto2.C
create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto3.C
create mode 100644 gcc/testsuite/g++.dg/cpp1y/decltype-auto4.C
create mode 100644 gcc/testsuite/g++.dg/cpp1z/decomp-decltype1.C
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index 0a002db14e7..e3ede02a48e 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -2421,7 +2421,8 @@ cp_fold (tree x)
if (REF_PARENTHESIZED_P (x))
{
tree p = maybe_undo_parenthesized_ref (x);
- return cp_fold (p);
+ if (p != x)
+ return cp_fold (p);
}
goto unary;
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 6b560952639..d3efc6ea238 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -29889,13 +29889,18 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
}
else if (AUTO_IS_DECLTYPE (auto_node))
{
+ /* Figure out if INIT is an unparenthesized id-expression or an
+ unparenthesized class member access. */
tree stripped_init = tree_strip_any_location_wrapper (init);
- if (REFERENCE_REF_P (stripped_init))
+ /* We need to be able to tell '(r)' and 'r' apart (when it's of
+ reference type). Only the latter is an id-expression. */
+ if (REFERENCE_REF_P (stripped_init)
+ && !REF_PARENTHESIZED_P (stripped_init))
stripped_init = TREE_OPERAND (stripped_init, 0);
- bool id = (DECL_P (stripped_init)
- || ((TREE_CODE (init) == COMPONENT_REF
- || TREE_CODE (init) == SCOPE_REF)
- && !REF_PARENTHESIZED_P (init)));
+ const bool id = (DECL_P (stripped_init)
+ || ((TREE_CODE (stripped_init) == COMPONENT_REF
+ || TREE_CODE (stripped_init) == SCOPE_REF)
+ && !REF_PARENTHESIZED_P (stripped_init)));
tree deduced = finish_decltype_type (init, id, complain);
deduced = canonicalize_type_argument (deduced, complain);
if (deduced == error_mark_node)
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index cd1956497f8..edba4b60e10 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -2049,7 +2049,8 @@ force_paren_expr (tree expr, bool even_uneval)
return expr;
if (TREE_CODE (expr) == COMPONENT_REF
- || TREE_CODE (expr) == SCOPE_REF)
+ || TREE_CODE (expr) == SCOPE_REF
+ || REFERENCE_REF_P (expr))
REF_PARENTHESIZED_P (expr) = true;
else if (DECL_P (tree_strip_any_location_wrapper (expr)))
{
@@ -2072,19 +2073,8 @@ maybe_undo_parenthesized_ref (tree t)
if (cxx_dialect < cxx14)
return t;
- if (INDIRECT_REF_P (t) && REF_PARENTHESIZED_P (t))
- {
- t = TREE_OPERAND (t, 0);
- while (TREE_CODE (t) == NON_LVALUE_EXPR
- || TREE_CODE (t) == NOP_EXPR)
- t = TREE_OPERAND (t, 0);
-
- gcc_assert (TREE_CODE (t) == ADDR_EXPR
- || TREE_CODE (t) == STATIC_CAST_EXPR);
- t = TREE_OPERAND (t, 0);
- }
- else if ((TREE_CODE (t) == PAREN_EXPR || TREE_CODE (t) == VIEW_CONVERT_EXPR)
- && REF_PARENTHESIZED_P (t))
+ if ((TREE_CODE (t) == PAREN_EXPR || TREE_CODE (t) == VIEW_CONVERT_EXPR)
+ && REF_PARENTHESIZED_P (t))
t = TREE_OPERAND (t, 0);
return t;
diff --git a/gcc/testsuite/g++.dg/cpp1y/decltype-auto2.C
b/gcc/testsuite/g++.dg/cpp1y/decltype-auto2.C
new file mode 100644
index 00000000000..56e011e36f4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/decltype-auto2.C
@@ -0,0 +1,12 @@
+// PR c++/103403
+// { dg-do compile { target c++14 } }
+
+template<typename T>
+auto constexpr RtoL1(T&& r) -> decltype(auto) {
+ return (r);
+};
+int main() {
+ int t;
+ int x{3};
+ decltype (RtoL1(x+0)) y = t;
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/decltype-auto3.C
b/gcc/testsuite/g++.dg/cpp1y/decltype-auto3.C
new file mode 100644
index 00000000000..914e87f5b79
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/decltype-auto3.C
@@ -0,0 +1,12 @@
+// PR c++/103403
+// { dg-do compile { target c++14 } }
+
+int main()
+{
+ int i = 1;
+ int&& r = 1;
+
+ decltype(auto) ri = (i);
+ decltype(auto) rr = (r);
+ decltype((r)) rr2 = (r);
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/decltype-auto4.C
b/gcc/testsuite/g++.dg/cpp1y/decltype-auto4.C
new file mode 100644
index 00000000000..9765857efb1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/decltype-auto4.C
@@ -0,0 +1,65 @@
+// PR c++/103403
+// { dg-do compile { target c++14 } }
+
+struct false_type { static constexpr bool value = false; };
+struct true_type { static constexpr bool value = true; };
+template<class T, class U>
+struct is_same : false_type {};
+template<class T>
+struct is_same<T, T> : true_type {};
+
+int fn ();
+int &ref ();
+int &&rref ();
+
+struct S {
+ int i;
+ int &r = i;
+};
+
+void
+ids ()
+{
+ const S *s = new S();
+ int i;
+ int &ir = i;
+ decltype(auto) r1 = s->i;
+ static_assert (is_same<decltype(r1), int>::value, "");
+ decltype(auto) r2 = s->r;
+ static_assert (is_same<decltype(r2), int&>::value, "");
+ decltype(auto) r3 = i;
+ static_assert (is_same<decltype(r3), int>::value, "");
+ decltype(auto) r4 = ir;
+ static_assert (is_same<decltype(r4), int&>::value, "");
+}
+
+void
+nonids ()
+{
+ const S *s = new S();
+ int i;
+ int &ir = i;
+ int &&irr = 42;
+ decltype(auto) r1 = fn ();
+ static_assert (is_same<decltype(r1), int>::value, "");
+ decltype(auto) r2 = (fn ());
+ static_assert (is_same<decltype(r2), int>::value, "");
+ decltype(auto) r3 = ref ();
+ static_assert (is_same<decltype(r3), int&>::value, "");
+ decltype(auto) r4 = (ref ());
+ static_assert (is_same<decltype(r4), int&>::value, "");
+ decltype(auto) r5 = rref ();
+ static_assert (is_same<decltype(r5), int&&>::value, "");
+ decltype(auto) r6 = (rref ());
+ static_assert (is_same<decltype(r6), int&&>::value, "");
+ decltype(auto) r8 = (s->i);
+ static_assert (is_same<decltype(r8), const int&>::value, "");
+ decltype(auto) r9 = (s->r);
+ static_assert (is_same<decltype(r9), int&>::value, "");
+ decltype(auto) r10 = (i);
+ static_assert (is_same<decltype(r10), int&>::value, "");
+ decltype(auto) r11 = (ir);
+ static_assert (is_same<decltype(r11), int&>::value, "");
+ decltype(auto) r12 = (irr);
+ static_assert (is_same<decltype(r12), int&>::value, "");
+}
diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp-decltype1.C
b/gcc/testsuite/g++.dg/cpp1z/decomp-decltype1.C
new file mode 100644
index 00000000000..e8ca0fc0bee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp-decltype1.C
@@ -0,0 +1,28 @@
+// PR c++/81176
+// { dg-do compile { target c++17 } }
+
+namespace std {
+ template<typename T> struct tuple_size;
+ template<int, typename> struct tuple_element;
+}
+
+struct A {
+ int i;
+ template <int I> int& get() { return i; }
+};
+
+template<> struct std::tuple_size<A> { static const int value = 2; };
+template<int I> struct std::tuple_element<I,A> { using type = int; };
+
+template <class,class> struct same_type;
+template <class T> struct same_type<T,T> {};
+
+void
+foo (A x)
+{
+ auto [ a, b ] = x;
+ decltype(auto) c = a;
+ same_type<decltype(a), int>{};
+ same_type<decltype(c), int>{};
+}
+
base-commit: c841dc0a4dd944cf8f76f414a286aedff1e38dce
