On Thu, Apr 21, 2022 at 08:56:23AM -0400, Jason Merrill wrote:
> 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.
Ah, that's what I misread -- [expr.context]/2.8 cares only about the right
operand :(.
> 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_*.
Yeah, that makes sense.
Bootstrap/regtest running on x86_64-pc-linux-gnu, ok for trunk/11.3 if it
passes?
-- >8 --
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.
Fixed by always passing false for 'lval' in cxx_eval_logical_expression;
there's no case where we actually expect an lvalue from a TRUTH_*.
PR c++/105321
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_logical_expression): Always pass false for lval
to cxx_eval_constant_expression.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-105321.C: New test.
---
gcc/cp/constexpr.cc | 9 ++++-----
gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C | 18 ++++++++++++++++++
2 files changed, 22 insertions(+), 5 deletions(-)
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..fa65290e938 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -4566,19 +4566,18 @@ cxx_eval_bit_cast (const constexpr_ctx *ctx, tree t,
bool *non_constant_p,
static tree
cxx_eval_logical_expression (const constexpr_ctx *ctx, tree t,
tree bailout_value, tree continue_value,
- bool lval,
- bool *non_constant_p, bool *overflow_p)
+ bool, bool *non_constant_p, bool *overflow_p)
{
tree r;
tree lhs = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0),
- lval,
- non_constant_p, overflow_p);
+ /*lval*/false, non_constant_p,
+ overflow_p);
VERIFY_CONSTANT (lhs);
if (tree_int_cst_equal (lhs, bailout_value))
return lhs;
gcc_assert (tree_int_cst_equal (lhs, continue_value));
r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 1),
- lval, non_constant_p,
+ /*lval*/false, non_constant_p,
overflow_p);
VERIFY_CONSTANT (r);
return r;
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: 1e6c0e69af8da436e1d1d2d23d8c38410d78ecf2
--
2.35.1
