On 11/8/21 15:03, Will Wray via Gcc-patches wrote:
This patch allows __builtin_bit_cast to materialize a C array as its To type.
It was developed as part of an implementation of P1997, array copy-semantics,
but is independent, so makes sense to submit, review and merge ahead of it.
gcc/cp/ChangeLog:
* constexpr.c (check_bit_cast_type): handle ARRAY_TYPE check,
(cxx_eval_bit_cast): handle ARRAY_TYPE copy.
* semantics.c (cp_build_bit_cast): warn only on unbounded/VLA.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/bit-cast2.C: update XFAIL tests.
* g++.dg/cpp2a/bit-cast-to-array1.C: New test.
---
gcc/cp/constexpr.c | 8 ++++-
gcc/cp/semantics.c | 7 ++---
gcc/testsuite/g++.dg/cpp2a/bit-cast-to-array1.C | 40 +++++++++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/bit-cast2.C | 8 ++---
4 files changed, 53 insertions(+), 10 deletions(-)
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 453007c686b..be1cdada6f8 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -4124,6 +4124,11 @@ static bool
check_bit_cast_type (const constexpr_ctx *ctx, location_t loc, tree type,
tree orig_type)
{
+ if (TREE_CODE (type) == ARRAY_TYPE)
+ return check_bit_cast_type (ctx, loc,
+ TYPE_MAIN_VARIANT (TREE_TYPE (type)),
+ orig_type);
+
if (TREE_CODE (type) == UNION_TYPE)
{
if (!ctx->quiet)
@@ -4280,7 +4285,8 @@ cxx_eval_bit_cast (const constexpr_ctx *ctx, tree t, bool
*non_constant_p,
tree r = NULL_TREE;
if (can_native_interpret_type_p (TREE_TYPE (t)))
r = native_interpret_expr (TREE_TYPE (t), ptr, len);
- else if (TREE_CODE (TREE_TYPE (t)) == RECORD_TYPE)
+ else if (TREE_CODE (TREE_TYPE (t)) == RECORD_TYPE
+ || TREE_CODE (TREE_TYPE (t)) == ARRAY_TYPE)
{
r = native_interpret_aggregate (TREE_TYPE (t), ptr, 0, len);
if (r != NULL_TREE)
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 2443d032749..b3126b12abc 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -11562,13 +11562,10 @@ cp_build_bit_cast (location_t loc, tree type, tree
arg,
{
if (!complete_type_or_maybe_complain (type, NULL_TREE, complain))
return error_mark_node;
- if (TREE_CODE (type) == ARRAY_TYPE)
+ if (TREE_CODE (type) == ARRAY_TYPE && !TYPE_DOMAIN (type))
{
- /* std::bit_cast for destination ARRAY_TYPE is not possible,
- as functions may not return an array, so don't bother trying
- to support this (and then deal with VLAs etc.). */
error_at (loc, "%<__builtin_bit_cast%> destination type %qT "
- "is an array type", type);
+ "is a VLA variable-length array type", type);
Null TYPE_DOMAIN doesn't mean VLA, it means unknown length.
Probably better to check for null or non-constant TYPE_SIZE rather than
specifically for VLA.
return error_mark_node;
}
if (!trivially_copyable_p (type))
diff --git a/gcc/testsuite/g++.dg/cpp2a/bit-cast-to-array1.C
b/gcc/testsuite/g++.dg/cpp2a/bit-cast-to-array1.C
new file mode 100644
index 00000000000..e6e50c06389
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/bit-cast-to-array1.C
@@ -0,0 +1,40 @@
+// { dg-do compile }
+
+class S { int s; };
+S s();
+class U { int a, b; };
+U u();
+
+void
+foo (int *q)
+{
+ __builtin_bit_cast (int [1], 0);
+ __builtin_bit_cast (S [1], 0);
+ __builtin_bit_cast (U [1], u);
+}
+
+template <int N>
+void
+bar (int *q)
+{
+ int intN[N] = {};
+ int int2N[2*N] = {};
+ __builtin_bit_cast (int [N], intN);
+ __builtin_bit_cast (S [N], intN);
+ __builtin_bit_cast (U [N], int2N);
+}
+
+template <typename T1, typename T2, typename T3>
+void
+baz (T1 ia, T2 sa, T3 ua)
+{
+ __builtin_bit_cast (T1, *ia);
+ __builtin_bit_cast (T2, *sa);
+ __builtin_bit_cast (T3, *ua);
+}
+
+void
+qux (S* sp, int *ip, U* up)
+{
+ baz <int[1], S[1], U[1]> (ip, sp, up);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/bit-cast2.C
b/gcc/testsuite/g++.dg/cpp2a/bit-cast2.C
index 6bb1760e621..7f1836ee4e9 100644
--- a/gcc/testsuite/g++.dg/cpp2a/bit-cast2.C
+++ b/gcc/testsuite/g++.dg/cpp2a/bit-cast2.C
@@ -14,7 +14,7 @@ foo (int *q)
__builtin_bit_cast (int, s); // { dg-error "'__builtin_bit_cast'
source type 'S' is not trivially copyable" }
__builtin_bit_cast (S, 0); // { dg-error "'__builtin_bit_cast'
destination type 'S' is not trivially copyable" }
__builtin_bit_cast (int &, q); // { dg-error "'__builtin_bit_cast' destination type
'int&' is not trivially copyable" }
- __builtin_bit_cast (int [1], 0); // { dg-error "'__builtin_bit_cast'
destination type \[^\n\r]* is an array type" }
+ __builtin_bit_cast (S [1], 0); // { dg-error "'__builtin_bit_cast'
destination type \[^\n\r]* is not trivially copyable" }
__builtin_bit_cast (V, 0); // { dg-error "invalid use of incomplete
type 'struct V'" }
__builtin_bit_cast (int, v);
__builtin_bit_cast (int, *p); // { dg-error "invalid use of
incomplete type 'struct V'" }
@@ -29,7 +29,7 @@ bar (int *q)
__builtin_bit_cast (int, s); // { dg-error "'__builtin_bit_cast'
source type 'S' is not trivially copyable" }
__builtin_bit_cast (S, 0); // { dg-error "'__builtin_bit_cast'
destination type 'S' is not trivially copyable" }
__builtin_bit_cast (int &, q); // { dg-error "'__builtin_bit_cast' destination type
'int&' is not trivially copyable" }
- __builtin_bit_cast (int [1], 0); // { dg-error "'__builtin_bit_cast'
destination type \[^\n\r]* is an array type" }
+ __builtin_bit_cast (S [1], 0); // { dg-error "'__builtin_bit_cast'
destination type \[^\n\r]* is not trivially copyable" }
__builtin_bit_cast (V, 0); // { dg-error "invalid use of incomplete
type 'struct V'" }
__builtin_bit_cast (int, *p); // { dg-error "invalid use of
incomplete type 'struct V'" }
__builtin_bit_cast (U, 0); // { dg-error "'__builtin_bit_cast' source
size '\[0-9]*' not equal to destination type size '\[0-9]*'" }
@@ -43,7 +43,7 @@ baz (T3 s, T4 *p, T1 *q)
__builtin_bit_cast (int, s); // { dg-error "'__builtin_bit_cast'
source type 'S' is not trivially copyable" }
__builtin_bit_cast (T3, 0); // { dg-error "'__builtin_bit_cast'
destination type 'S' is not trivially copyable" }
__builtin_bit_cast (T1 &, q); // { dg-error "'__builtin_bit_cast'
destination type 'int&' is not trivially copyable" }
- __builtin_bit_cast (T2, 0); // { dg-error "'__builtin_bit_cast'
destination type \[^\n\r]* is an array type" }
+ __builtin_bit_cast (T2, 0); // { dg-error "'__builtin_bit_cast'
destination type \[^\n\r]* is not trivially copyable" }
__builtin_bit_cast (T4, 0); // { dg-error "invalid use of incomplete
type 'struct V'" }
__builtin_bit_cast (int, *p); // { dg-error "invalid use of
incomplete type 'struct V'" }
__builtin_bit_cast (U, (T1) 0); // { dg-error "'__builtin_bit_cast' source
size '\[0-9]*' not equal to destination type size '\[0-9]*'" }
@@ -53,5 +53,5 @@ baz (T3 s, T4 *p, T1 *q)
void
qux (int *q)
{
- baz <int, int [1], S, V> (s, p, q);
+ baz <int, S [1], S, V> (s, p, q);
}
