On 2/15/22 15:13, Patrick Palka wrote:
On Tue, 15 Feb 2022, Patrick Palka wrote:
Here we're crashing from potential_constant_expression because it tries
to perform trial evaluation of the first operand '(bool)__r' of the
conjunction (which is overall wrapped in a NON_DEPENDENT_EXPR), but
cxx_eval_constant_expression ICEs on unhandled trees (of which CAST_EXPR
is one).
Since cxx_eval_constant_expression always treats NON_DEPENDENT_EXPR
as non-constant, and since NON_DEPENDENT_EXPR is also opaque to
instantiate_non_dependent_expr, it seems futile to have p_c_e_1 ever
return true for NON_DEPENDENT_EXPR, so let's just instead return false
and avoid recursing.
Well, in a template we use pce1 to decide whether to complain about
something that needs to be constant but can't be. We aren't trying to
get a value yet.
Actually, why are we seeing a NON_DEPENDENT_EXPR here? Did it leak into
the AST somehow? They should all be temporary within build_x_whatever
functions.
Alternatively p_c_e_1 could continue to recurse into NON_DEPENDENT_EXPR,
but with trial evaluation disabled by setting processing_template_decl,
but as mentioned it seems pointless for p_c_e_1 to ever return true for
NON_DEPENDENT_EXPR.
...
Since we're not issuing a diagnostic in this case, I suppose we should
also assert that tf_error isn't set. Bootstrapped and regtested on
x86_64-pc-linux-gnu.
-- >8 --
PR c++/104507
gcc/cp/ChangeLog:
* constexpr.cc (potential_constant_expression_1)
<case NON_DEPENDENT_EXPR>: Return false instead of recursing.
Assert tf_error isn't set.
gcc/testsuite/ChangeLog:
* g++.dg/template/non-dependent21.C: New test.
---
gcc/cp/constexpr.cc | 5 ++++-
gcc/testsuite/g++.dg/template/non-dependent21.C | 9 +++++++++
2 files changed, 13 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/template/non-dependent21.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 7274c3b760e..b363ef08411 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -9065,6 +9065,10 @@ potential_constant_expression_1 (tree t, bool want_rval,
bool strict, bool now,
case BIND_EXPR:
return RECUR (BIND_EXPR_BODY (t), want_rval);
+ case NON_DEPENDENT_EXPR:
+ gcc_checking_assert (!(flags & tf_error));
+ return false;
+
case CLEANUP_POINT_EXPR:
case MUST_NOT_THROW_EXPR:
case TRY_CATCH_EXPR:
@@ -9072,7 +9076,6 @@ potential_constant_expression_1 (tree t, bool want_rval,
bool strict, bool now,
case EH_SPEC_BLOCK:
case EXPR_STMT:
case PAREN_EXPR:
- case NON_DEPENDENT_EXPR:
/* For convenience. */
case LOOP_EXPR:
case EXIT_EXPR:
diff --git a/gcc/testsuite/g++.dg/template/non-dependent21.C
b/gcc/testsuite/g++.dg/template/non-dependent21.C
new file mode 100644
index 00000000000..89900837b8b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent21.C
@@ -0,0 +1,9 @@
+// PR c++/104507
+
+extern const char *_k_errmsg[];
+
+template<class>
+const char* DoFoo(int __r, int __s) {
+ const char* n = _k_errmsg[(bool)__r && __s ? 1 : 2];
+ return n;
+}
