On Tue, 19 Jan 2021, Jason Merrill wrote:
> On 1/13/21 12:05 PM, Patrick Palka wrote:
> > In the below testcase, the expression of the atomic constraint after
> > substitution is (int *) NON_LVALUE_EXPR <1> != 0B which is not a C++
> > constant expression, but its TREE_CONSTANT flag is set (from build2),
> > so satisfy_atom fails to notice that it's non-constant (and we end
> > up tripping over the assert in satisfaction_value).
> >
> > Since TREE_CONSTANT doesn't necessarily correspond to C++ constantness,
> > this patch makes satisfy_atom instead check is_rvalue_constant_expression.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > trunk/10?
> >
> > gcc/cp/ChangeLog:
> >
> > PR c++/98644
> > * constraint.cc (satisfy_atom): Check is_rvalue_constant_expression
> > instead of TREE_CONSTANT.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR c++/98644
> > * g++.dg/cpp2a/concepts-pr98644.C: New test.
> > ---
> > gcc/cp/constraint.cc | 2 +-
> > gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C | 7 +++++++
> > 2 files changed, 8 insertions(+), 1 deletion(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C
> >
> > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > index 9049d087859..f99a25dc8a4 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -2969,7 +2969,7 @@ satisfy_atom (tree t, tree args, sat_info info)
> > {
> > result = maybe_constant_value (result, NULL_TREE,
> > /*manifestly_const_eval=*/true);
> > - if (!TREE_CONSTANT (result))
>
> This should be sufficient. If the result isn't constant, maybe_constant_value
> shouldn't return it with TREE_CONSTANT set. See
>
> > /* This isn't actually constant, so unset TREE_CONSTANT.
> >
>
> in cxx_eval_outermost_constant_expr.
I see, so the problem seems to be that the fail-fast path of
maybe_constant_value isn't clearing TREE_CONSTANT sufficiently. Would
it make sense to fix this like so?
-- >8 --
Subject: [PATCH] c++: ICE with non-constant satisfaction value [PR98644]
Here during satisfaction the expression of the atomic constraint after
substitution is (int *) NON_LVALUE_EXPR <1> != 0B, which is not a C++
constant expression due to the reinterpret_cast, but TREE_CONSTANT is
set since its value is otherwise effectively constant. We then call
maybe_constant_value on it, which proceeds via its fail-fast path to
exit early without clearing TREE_CONSTANT. But satisfy_atom relies
on checking TREE_CONSTANT of the result of maybe_constant_value in order
to detect non-constant satisfaction.
This patch fixes this by making the fail-fast path of maybe_constant_value
clear TREE_CONSTANT in this case, like cxx_eval_outermost_constant_expr
in the normal path would have done.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
PR c++/98644
gcc/cp/ChangeLog:
* constexpr.cc (maybe_constant_value): In the fail-fast path,
clear TREE_CONSTANT on the result if it's set on the input.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-pr98644.C: New test.
* g++.dg/parse/array-size2.C: Remove expected diagnostic about a
narrowing conversion.
---
gcc/cp/constexpr.cc | 4 +++-
gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C | 7 +++++++
gcc/testsuite/g++.dg/parse/array-size2.C | 2 --
3 files changed, 10 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 4716694cb71..234cf0acc26 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -7965,8 +7965,10 @@ maybe_constant_value (tree t, tree decl, bool
manifestly_const_eval)
if (!is_nondependent_constant_expression (t))
{
- if (TREE_OVERFLOW_P (t))
+ if (TREE_OVERFLOW_P (t)
+ || (!processing_template_decl && TREE_CONSTANT (t)))
{
+ /* This isn't actually constant, so unset TREE_CONSTANT. */
t = build_nop (TREE_TYPE (t), t);
TREE_CONSTANT (t) = false;
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C
new file mode 100644
index 00000000000..6772f72a3ce
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C
@@ -0,0 +1,7 @@
+// PR c++/98644
+// { dg-do compile { target c++20 } }
+
+template<class T> concept Signed = bool(T(1)); // { dg-error
"reinterpret_cast" }
+static_assert(Signed<int*>); // { dg-error "non-constant" }
+
+constexpr bool B = requires { requires bool((char *)1); }; // { dg-error
"reinterpret_cast" }
diff --git a/gcc/testsuite/g++.dg/parse/array-size2.C
b/gcc/testsuite/g++.dg/parse/array-size2.C
index c4a69df3b01..e58fe266e77 100644
--- a/gcc/testsuite/g++.dg/parse/array-size2.C
+++ b/gcc/testsuite/g++.dg/parse/array-size2.C
@@ -15,8 +15,6 @@ void
foo (void)
{
char g[(char *) &((struct S *) 0)->b - (char *) 0]; // { dg-error "40:size
of array .g. is not an integral constant-expression" }
- // { dg-error "narrowing
conversion" "" { target c++11 } .-1 }
- // { dg-message
"expression has a constant value but is not a C.. constant-expression" "" {
target c++11 } .-2 }
char h[(__SIZE_TYPE__) &((struct S *) 8)->b]; // { dg-error
"10:size of array .h. is not an integral constant-expression" }
bar (g, h);
}
--
2.35.1.354.g715d08a9e5
