On Thu, 10 Mar 2022, Jason Merrill wrote:
> On 3/1/22 00:10, Patrick Palka wrote:
> > 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);
>
> build_nop isn't appropriate for arbitrary expressions (classes, in
> particular). We probably want to factor out the code in
> cxx_eval_outermost_constant_expr under the "this isn't actually constant"
> comment.
Gotcha, makes sense. Like the following? Bootstrapped and regtested on
x86_64-pc-linux-gnu.
-- >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.
PR c++/98644
gcc/cp/ChangeLog:
* constexpr.cc (mark_non_constant): Define, split out from ...
(cxx_eval_outermost_constant_expr): ... here.
(maybe_constant_value): Use it.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-pr98644.C: New test.
* g++.dg/parse/array-size2.C: Remove expected diagnostic about a
narrowing conversion.
Co-authored-by: Jason Merrill <[email protected]>
---
gcc/cp/constexpr.cc | 46 +++++++++++--------
gcc/testsuite/g++.dg/cpp2a/concepts-pr98644.C | 7 +++
gcc/testsuite/g++.dg/parse/array-size2.C | 2 -
3 files changed, 34 insertions(+), 21 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..22d86f023d0 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -7579,6 +7579,29 @@ find_immediate_fndecl (tree *tp, int */*walk_subtrees*/,
void */*data*/)
return NULL_TREE;
}
+/* T has TREE_CONSTANT set but has been deemed not a valid C++ constant
+ expression. Return a version of T that has TREE_CONSTANT cleared. */
+
+static tree
+mark_non_constant (tree t)
+{
+ gcc_checking_assert (TREE_CONSTANT (t));
+
+ /* This isn't actually constant, so unset TREE_CONSTANT.
+ Don't clear TREE_CONSTANT on ADDR_EXPR, as the middle-end requires
+ it to be set if it is invariant address, even when it is not
+ a valid C++ constant expression. Wrap it with a NOP_EXPR
+ instead. */
+ if (EXPR_P (t) && TREE_CODE (t) != ADDR_EXPR)
+ t = copy_node (t);
+ else if (TREE_CODE (t) == CONSTRUCTOR)
+ t = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (t), t);
+ else
+ t = build_nop (TREE_TYPE (t), t);
+ TREE_CONSTANT (t) = false;
+ return t;
+}
+
/* ALLOW_NON_CONSTANT is false if T is required to be a constant expression.
STRICT has the same sense as for constant_value_1: true if we only allow
conforming C++ constant expressions, or false if we want a constant value
@@ -7801,20 +7824,7 @@ cxx_eval_outermost_constant_expr (tree t, bool
allow_non_constant,
else if (constexpr_dtor)
return r;
else if (non_constant_p && TREE_CONSTANT (r))
- {
- /* This isn't actually constant, so unset TREE_CONSTANT.
- Don't clear TREE_CONSTANT on ADDR_EXPR, as the middle-end requires
- it to be set if it is invariant address, even when it is not
- a valid C++ constant expression. Wrap it with a NOP_EXPR
- instead. */
- if (EXPR_P (r) && TREE_CODE (r) != ADDR_EXPR)
- r = copy_node (r);
- else if (TREE_CODE (r) == CONSTRUCTOR)
- r = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (r), r);
- else
- r = build_nop (TREE_TYPE (r), r);
- TREE_CONSTANT (r) = false;
- }
+ r = mark_non_constant (r);
else if (non_constant_p)
return t;
@@ -7965,11 +7975,9 @@ maybe_constant_value (tree t, tree decl, bool
manifestly_const_eval)
if (!is_nondependent_constant_expression (t))
{
- if (TREE_OVERFLOW_P (t))
- {
- t = build_nop (TREE_TYPE (t), t);
- TREE_CONSTANT (t) = false;
- }
+ if (TREE_OVERFLOW_P (t)
+ || (!processing_template_decl && TREE_CONSTANT (t)))
+ t = mark_non_constant (t);
return t;
}
else if (CONSTANT_CLASS_P (t))
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);
}
--
2.35.1.455.g1a4874565f
