On 4/20/22 18:40, Marek Polacek wrote:
Here we issue a bogus error for the first assert in the test. Therein
we have
<retval> = (void) (VIEW_CONVERT_EXPR<bool>(yes) || handle_error ());,
VIEW_CONVERT_EXPR<int>(value);
which has a COMPOUND_EXPR, so we get to cxx_eval_constant_expression
<case COMPOUND_EXPR>. The problem here is that we call
7044 /* Check that the LHS is constant and then discard it. */
7045 cxx_eval_constant_expression (ctx, op0,
7046 true, non_constant_p, overflow_p,
7047 jump_target);
where lval is always true, so the PARM_DECL 'yes' is not evaluated into
its value. r218832 changed the argument for 'lval' from false to true:
(cxx_eval_constant_expression) [COMPOUND_EXPR]: Pass true for lval.
but I think we want to pass 'lval' instead. Jakub tells me that's what
we do for "(void) expr" as well. [expr.comma] says that the left expression
is a discarded-value expression, but [expr.context] doesn't suggest that
we should always be passing false for lval as pre-r218832.
In a discarded-value expression, we don't do the lvalue-rvalue
conversion; whether we want an lvalue for the RHS of the comma is
irrelevant.
The bug here seems to be that we aren't doing the l->r conversion for
the LHS of the TRUTH_OR_EXPR; I'd think that cxx_eval_logical_expression
should pass false for lval to both recursive calls, there's no case
where we actually expect an lvalue from a TRUTH_*.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11.3?
PR c++/105321
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_constant_expression) <case COMPOUND_EXPR>: Pass
lval to cxx_eval_constant_expression.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-105321.C: New test.
---
gcc/cp/constexpr.cc | 2 +-
gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C | 18 ++++++++++++++++++
2 files changed, 19 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index e89440e770f..28271d4405d 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -7043,7 +7043,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx,
tree t,
{
/* Check that the LHS is constant and then discard it. */
cxx_eval_constant_expression (ctx, op0,
- true, non_constant_p, overflow_p,
+ lval, non_constant_p, overflow_p,
jump_target);
if (*non_constant_p)
return t;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C
new file mode 100644
index 00000000000..adb6830ff22
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C
@@ -0,0 +1,18 @@
+// PR c++/105321
+// { dg-do compile { target c++11 } }
+
+bool handle_error();
+
+constexpr int echo(int value, bool yes = true) noexcept
+{
+ return (yes || handle_error()), value;
+}
+
+static_assert(echo(10) == 10, "");
+
+constexpr int echo2(int value, bool no = false) noexcept
+{
+ return (!no || handle_error()), value;
+}
+
+static_assert(echo2(10) == 10, "");
base-commit: 5bde80f48bcc594658c788895ad1fd86d0916fc2
