On Thu, Dec 20, 2018 at 04:26:21PM -0500, Jason Merrill wrote:
> Right, but they either are or they aren't. Doing this isn't likely to help
> anything, and can lead to paradoxical results in contrived testcases.
>
> > But if you think this is a bad idea, I can remove it, I haven't been
> > successful in constructing a testcase where this would matter.
>
> Please. OK with those changes.
Actually, the main reason for any changes in that block was mainly that I
thought
it is a bad idea to fold the argument with __builtin_is_const_evaluated ()
folded into true if that argument isn't a constant expression.
So are you ok with what is in the patch below, i.e.
{
bool non_cst_p = false, ovf_p = false;
tree a = cxx_eval_constant_expression (&new_ctx, args[i], false,
&non_cst_p, &ovf_p);
if ((!non_cst_p && !ovf_p) || !ctx->manifestly_const_eval)
args[i] = a;
}
, or perhaps without the || !ctx->manifestly_const_eval? So, if the
argument is a constant expression, fold to that, if it is not, just do
cp_fully_fold on it if it is __builtin_constant_p, otherwise nothing?
2018-12-20 Jakub Jelinek <ja...@redhat.com>
PR c++/86524
PR c++/88446
* cp-tree.h (fold_non_dependent_expr): Add manifestly_const_eval
argument.
* constexpr.c (cxx_eval_builtin_function_call): Evaluate
__builtin_constant_p if ctx->manifestly_const_eval even in constexpr
functions. For arguments to builtins, if ctx->manifestly_const_eval
and argument is not a constant expression, use original argument.
Fix comment typo.
(fold_non_dependent_expr): Add manifestly_const_eval argument, pass
it through to cxx_eval_outermost_constant_expr and
maybe_constant_value.
* semantics.c (finish_static_assert): Call fold_non_dependent_expr
with true as manifestly_const_eval.
* g++.dg/cpp1y/constexpr-86524.C: New test.
* g++.dg/cpp2a/is-constant-evaluated4.C: New test.
* g++.dg/cpp2a/is-constant-evaluated5.C: New test.
* g++.dg/cpp2a/is-constant-evaluated6.C: New test.
--- gcc/cp/cp-tree.h.jj 2018-12-20 18:29:24.069715207 +0100
+++ gcc/cp/cp-tree.h 2018-12-20 22:10:46.686521475 +0100
@@ -7668,7 +7668,9 @@ extern tree cxx_constant_value (tree,
extern tree cxx_constant_init (tree, tree = NULL_TREE);
extern tree maybe_constant_value (tree, tree = NULL_TREE, bool =
false);
extern tree maybe_constant_init (tree, tree =
NULL_TREE, bool = false);
-extern tree fold_non_dependent_expr (tree, tsubst_flags_t =
tf_warning_or_error);
+extern tree fold_non_dependent_expr (tree,
+ tsubst_flags_t =
tf_warning_or_error,
+ bool = false);
extern tree fold_simple (tree);
extern bool is_sub_constant_expr (tree);
extern bool reduced_constant_expression_p (tree);
--- gcc/cp/constexpr.c.jj 2018-12-20 08:50:29.695444227 +0100
+++ gcc/cp/constexpr.c 2018-12-20 22:12:43.754615737 +0100
@@ -1197,7 +1197,7 @@ cxx_eval_builtin_function_call (const co
/* If we aren't requiring a constant expression, defer __builtin_constant_p
in a constexpr function until we have values for the parameters. */
if (bi_const_p
- && ctx->quiet
+ && !ctx->manifestly_const_eval
&& current_function_decl
&& DECL_DECLARED_CONSTEXPR_P (current_function_decl))
{
@@ -1222,7 +1222,6 @@ cxx_eval_builtin_function_call (const co
return constant false for a non-constant argument. */
constexpr_ctx new_ctx = *ctx;
new_ctx.quiet = true;
- bool dummy1 = false, dummy2 = false;
for (i = 0; i < nargs; ++i)
{
args[i] = CALL_EXPR_ARG (t, i);
@@ -1231,10 +1230,16 @@ cxx_eval_builtin_function_call (const co
of the builtin, verify it here. */
if (!builtin_valid_in_constant_expr_p (fun)
|| potential_constant_expression (args[i]))
- args[i] = cxx_eval_constant_expression (&new_ctx, args[i], false,
- &dummy1, &dummy2);
+ {
+ bool non_cst_p = false, ovf_p = false;
+ tree a = cxx_eval_constant_expression (&new_ctx, args[i], false,
+ &non_cst_p, &ovf_p);
+ if ((!non_cst_p && !ovf_p) || !ctx->manifestly_const_eval)
+ args[i] = a;
+ }
+
if (bi_const_p)
- /* For __built_in_constant_p, fold all expressions with constant values
+ /* For __builtin_constant_p, fold all expressions with constant values
even if they aren't C++ constant-expressions. */
args[i] = cp_fully_fold (args[i]);
}
@@ -5340,6 +5345,7 @@ clear_cv_and_fold_caches (void)
(t, complain) followed by maybe_constant_value but is more efficient,
because it calls instantiation_dependent_expression_p and
potential_constant_expression at most once.
+ The manifestly_const_eval argument is passed to maybe_constant_value.
Callers should generally pass their active complain, or if they are in a
non-template, diagnosing context, they can use the default of
@@ -5350,7 +5356,8 @@ clear_cv_and_fold_caches (void)
tree
fold_non_dependent_expr (tree t,
- tsubst_flags_t complain /* = tf_warning_or_error */)
+ tsubst_flags_t complain /* = tf_warning_or_error */,
+ bool manifestly_const_eval /* = false */)
{
if (t == NULL_TREE)
return NULL_TREE;
@@ -5380,7 +5387,8 @@ fold_non_dependent_expr (tree t,
return t;
}
- tree r = cxx_eval_outermost_constant_expr (t, true, true, false,
+ tree r = cxx_eval_outermost_constant_expr (t, true, true,
+ manifestly_const_eval,
NULL_TREE);
/* cp_tree_equal looks through NOPs, so allow them. */
gcc_checking_assert (r == t
@@ -5398,7 +5406,7 @@ fold_non_dependent_expr (tree t,
return t;
}
- return maybe_constant_value (t);
+ return maybe_constant_value (t, NULL_TREE, manifestly_const_eval);
}
/* Like maybe_constant_value, but returns a CONSTRUCTOR directly, rather
--- gcc/cp/semantics.c.jj 2018-12-20 08:50:29.712443949 +0100
+++ gcc/cp/semantics.c 2018-12-20 22:10:46.690521410 +0100
@@ -9225,7 +9225,8 @@ finish_static_assert (tree condition, tr
/* Fold the expression and convert it to a boolean value. */
condition = perform_implicit_conversion_flags (boolean_type_node, condition,
complain, LOOKUP_NORMAL);
- condition = fold_non_dependent_expr (condition, complain);
+ condition = fold_non_dependent_expr (condition, complain,
+ /*manifestly_const_eval=*/true);
if (TREE_CODE (condition) == INTEGER_CST && !integer_zerop (condition))
/* Do nothing; the condition is satisfied. */
--- gcc/testsuite/g++.dg/cpp1y/constexpr-86524.C.jj 2018-12-20
22:10:46.690521410 +0100
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-86524.C 2018-12-20
22:10:46.690521410 +0100
@@ -0,0 +1,41 @@
+// PR c++/86524
+// { dg-do run { target c++14 } }
+// { dg-options "-O2" }
+
+extern "C" void abort ();
+typedef __UINTPTR_TYPE__ uintptr_t;
+
+constexpr bool
+foo (const int *x, const int *y)
+{
+ if (__builtin_constant_p (x < y))
+ return x < y;
+ return (uintptr_t) x < (uintptr_t) y;
+}
+
+void
+bar ()
+{
+ constexpr int x = 0;
+ static_assert (!(&x < &x));
+ static_assert (!foo (&x, &x));
+}
+
+constexpr void
+baz ()
+{
+ constexpr int x = 0;
+ static_assert (!(&x < &x));
+ static_assert (!foo (&x, &x));
+}
+
+int i, j;
+
+int
+main ()
+{
+ bar ();
+ baz ();
+ if (!(foo (&i, &j) ^ foo (&j, &i)))
+ abort ();
+}
--- gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated4.C.jj 2018-12-20
22:10:46.691521394 +0100
+++ gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated4.C 2018-12-20
22:10:46.691521394 +0100
@@ -0,0 +1,19 @@
+// P0595R2
+// { dg-do compile { target c++14 } }
+
+namespace std {
+ constexpr inline bool
+ is_constant_evaluated () noexcept
+ {
+ return __builtin_is_constant_evaluated ();
+ }
+}
+
+constexpr int
+foo () noexcept
+{
+ return std::is_constant_evaluated () ? 5 : 12;
+}
+
+static_assert (std::is_constant_evaluated (), "");
+static_assert (foo () == 5, "");
--- gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated5.C.jj 2018-12-20
22:10:46.691521394 +0100
+++ gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated5.C 2018-12-20
22:10:46.691521394 +0100
@@ -0,0 +1,41 @@
+// PR c++/86524
+// { dg-do run { target c++14 } }
+// { dg-options "-O2" }
+
+extern "C" void abort ();
+typedef __UINTPTR_TYPE__ uintptr_t;
+
+constexpr bool
+foo (const int *x, const int *y)
+{
+ if (__builtin_is_constant_evaluated ())
+ return x < y;
+ return (uintptr_t) x < (uintptr_t) y;
+}
+
+void
+bar ()
+{
+ constexpr int x = 0;
+ static_assert (!(&x < &x));
+ static_assert (!foo (&x, &x));
+}
+
+constexpr void
+baz ()
+{
+ constexpr int x = 0;
+ static_assert (!(&x < &x));
+ static_assert (!foo (&x, &x));
+}
+
+int i, j;
+
+int
+main ()
+{
+ bar ();
+ baz ();
+ if (!(foo (&i, &j) ^ foo (&j, &i)))
+ abort ();
+}
--- gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated6.C.jj 2018-12-20
22:10:46.691521394 +0100
+++ gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated6.C 2018-12-20
22:10:46.691521394 +0100
@@ -0,0 +1,29 @@
+// P0595R2
+// { dg-do compile { target c++14 } }
+
+namespace std {
+ constexpr inline bool
+ is_constant_evaluated () noexcept
+ {
+ return __builtin_is_constant_evaluated ();
+ }
+}
+
+int a;
+
+constexpr bool
+foo (int x)
+{
+ return __builtin_constant_p (x);
+}
+
+constexpr bool
+bar (int x)
+{
+ return __builtin_constant_p (x + a);
+}
+
+static_assert (__builtin_constant_p (0) + 2 * std::is_constant_evaluated () ==
3, "");
+static_assert (__builtin_constant_p (a) + 2 * std::is_constant_evaluated () ==
2, "");
+static_assert (foo (0) + 2 * std::is_constant_evaluated () == 3, "");
+static_assert (bar (0) + 2 * std::is_constant_evaluated () == 2, "");
Jakub
