* [pushed] c++: strict constexpr and local vars
@ 2022-05-24 20:03 Jason Merrill
0 siblings, 0 replies; 2+ messages in thread
From: Jason Merrill @ 2022-05-24 20:03 UTC (permalink / raw)
To: gcc-patches
A change I was working on made constexpr_searcher.cc start to fail, and when
I looked at it I wondered why it had been accepted before. This turned out
to be because we try to be more flexible about constant-evaluation of static
initializers, as allowed, but we were wrongly doing the same for non-static
initializers as well.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog:
* constexpr.cc (maybe_constant_init_1): Only pass false for
strict when initializing a variable of static duration.
libstdc++-v3/ChangeLog:
* testsuite/20_util/function_objects/constexpr_searcher.cc: Add
constexpr.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-local4.C: New test.
---
gcc/cp/constexpr.cc | 12 +++++++++---
gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C | 17 +++++++++++++++++
.../function_objects/constexpr_searcher.cc | 4 ++--
3 files changed, 28 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 388239ea8a8..1a70fda1dc5 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -8301,9 +8301,15 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant,
else if (CONSTANT_CLASS_P (t) && allow_non_constant)
/* No evaluation needed. */;
else
- t = cxx_eval_outermost_constant_expr (t, allow_non_constant,
- /*strict*/false,
- manifestly_const_eval, false, decl);
+ {
+ /* [basic.start.static] allows constant-initialization of variables with
+ static or thread storage duration even if it isn't required, but we
+ shouldn't bend the rules the same way for automatic variables. */
+ bool is_static = (decl && DECL_P (decl)
+ && (TREE_STATIC (decl) || DECL_EXTERNAL (decl)));
+ t = cxx_eval_outermost_constant_expr (t, allow_non_constant, !is_static,
+ manifestly_const_eval, false, decl);
+ }
if (TREE_CODE (t) == TARGET_EXPR)
{
tree init = TARGET_EXPR_INITIAL (t);
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C
new file mode 100644
index 00000000000..bef62488579
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C
@@ -0,0 +1,17 @@
+// { dg-do compile { target c++14 } }
+
+struct A
+{
+ int i;
+ constexpr A(int i): i(i) {};
+};
+
+const A a = 42;
+
+constexpr int f()
+{
+ const int j = a.i; // { dg-message "'a'" }
+ return j;
+}
+
+static_assert (f() == 42,""); // { dg-error "non-constant" }
diff --git a/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc b/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc
index 33012200cb0..17069694c1b 100644
--- a/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc
+++ b/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc
@@ -28,13 +28,13 @@
#include <string_view>
-const std::string_view
+constexpr std::string_view
patt = "World";
constexpr std::string_view
greet = "Hello, Humongous World of Wonder!!!";
-const std::wstring_view
+constexpr std::wstring_view
wpatt = L"World";
constexpr std::wstring_view
base-commit: 1189c03859cefef4fc4fd44d57eb3d4d3348b562
--
2.27.0
^ permalink raw reply [flat|nested] 2+ messages in thread
* [pushed] c++: strict constexpr and local vars
@ 2022-05-25 15:08 Jason Merrill
0 siblings, 0 replies; 2+ messages in thread
From: Jason Merrill @ 2022-05-25 15:08 UTC (permalink / raw)
To: gcc-patches
A change I was working on made constexpr_searcher.cc start to fail, and when
I looked at it I wondered why it had been accepted before. This turned out
to be because we try to be more flexible about constant-evaluation of static
initializers, as allowed, but we were wrongly doing the same for non-static
initializers as well.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog:
* constexpr.cc (maybe_constant_init_1): Only pass false for
strict when initializing a variable of static duration.
libstdc++-v3/ChangeLog:
* testsuite/20_util/function_objects/constexpr_searcher.cc: Add
constexpr.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-local4.C: New test.
---
gcc/cp/constexpr.cc | 12 +++++++++---
gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C | 17 +++++++++++++++++
.../function_objects/constexpr_searcher.cc | 4 ++--
3 files changed, 28 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 388239ea8a8..1a70fda1dc5 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -8301,9 +8301,15 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant,
else if (CONSTANT_CLASS_P (t) && allow_non_constant)
/* No evaluation needed. */;
else
- t = cxx_eval_outermost_constant_expr (t, allow_non_constant,
- /*strict*/false,
- manifestly_const_eval, false, decl);
+ {
+ /* [basic.start.static] allows constant-initialization of variables with
+ static or thread storage duration even if it isn't required, but we
+ shouldn't bend the rules the same way for automatic variables. */
+ bool is_static = (decl && DECL_P (decl)
+ && (TREE_STATIC (decl) || DECL_EXTERNAL (decl)));
+ t = cxx_eval_outermost_constant_expr (t, allow_non_constant, !is_static,
+ manifestly_const_eval, false, decl);
+ }
if (TREE_CODE (t) == TARGET_EXPR)
{
tree init = TARGET_EXPR_INITIAL (t);
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C
new file mode 100644
index 00000000000..bef62488579
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-local4.C
@@ -0,0 +1,17 @@
+// { dg-do compile { target c++14 } }
+
+struct A
+{
+ int i;
+ constexpr A(int i): i(i) {};
+};
+
+const A a = 42;
+
+constexpr int f()
+{
+ const int j = a.i; // { dg-message "'a'" }
+ return j;
+}
+
+static_assert (f() == 42,""); // { dg-error "non-constant" }
diff --git a/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc b/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc
index 33012200cb0..17069694c1b 100644
--- a/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc
+++ b/libstdc++-v3/testsuite/20_util/function_objects/constexpr_searcher.cc
@@ -28,13 +28,13 @@
#include <string_view>
-const std::string_view
+constexpr std::string_view
patt = "World";
constexpr std::string_view
greet = "Hello, Humongous World of Wonder!!!";
-const std::wstring_view
+constexpr std::wstring_view
wpatt = L"World";
constexpr std::wstring_view
base-commit: 1b661f3f5e712c951e774b3b91fffe4dac734cc7
--
2.27.0
^ permalink raw reply [flat|nested] 2+ messages in thread
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