On Tue, Feb 09, 2021 at 04:08:03PM -0500, Jason Merrill via Gcc-patches wrote:
> > They are not in the symtab from the C++ FE. And we don't allow those
> > VAR_DECLs or their
> > addresses to leak into the IL anyway.
> > But, they are TREE_STATIC because pretending they are automatic didn't
> > really work (e.g. address of automatic variables is not a constant
> > expression).
> > The generic folding code uses maybe_nonzero_address predicate which
> > apprently creates a symtab entry for them but as nothing uses them they
> > won't be emitted.
>
> Ah.
>
> > If we wanted to avoid that, we'd need to either add some generic VAR_DECL
> > bit for those vars or add a target hook that would return true for them and
> > then handle them in the middle-end.
>
> I'm surprised that nonzero_address has such a limited set of things it will
> actually believe have non-zero addresses with
> -fno-delete-null-pointer-checks. But it seems that we should be able to
> arrange to satisfy
>
> > if (definition && !DECL_EXTERNAL (decl)
>
> since these "variables" are indeed defined within the current translation
> unit.
Doing that seems to work and as added benefit it fixes another PR that has
been filed recently. I need to create the varpool node explicitly and call
a method that sets the definition member in there, but I can also unregister
those varpool nodes at the end of constexpr processing, as the processing
ensured they don't leak outside of the processing.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2021-02-10 Jakub Jelinek <ja...@redhat.com>
PR c++/98988
PR c++/99031
* constexpr.c: Include cgraph.h.
(cxx_eval_call_expression): Call varpool_node::finalize_decl on
heap artificial vars.
(cxx_eval_outermost_constant_expr): Remove varpool nodes for
heap artificial vars.
* g++.dg/cpp2a/constexpr-new16.C: New test.
* g++.dg/cpp2a/constexpr-new17.C: New test.
--- gcc/cp/constexpr.c.jj 2021-02-09 10:05:28.820833601 +0100
+++ gcc/cp/constexpr.c 2021-02-10 11:31:16.567984809 +0100
@@ -35,6 +35,7 @@ along with GCC; see the file COPYING3.
#include "timevar.h"
#include "fold-const-call.h"
#include "stor-layout.h"
+#include "cgraph.h"
static bool verify_constant (tree, bool, bool *, bool *);
#define VERIFY_CONSTANT(X) \
@@ -2340,6 +2341,7 @@ cxx_eval_call_expression (const constexp
type);
DECL_ARTIFICIAL (var) = 1;
TREE_STATIC (var) = 1;
+ varpool_node::finalize_decl (var);
ctx->global->heap_vars.safe_push (var);
ctx->global->values.put (var, NULL_TREE);
return fold_convert (ptr_type_node, build_address (var));
@@ -7199,15 +7201,18 @@ cxx_eval_outermost_constant_expr (tree t
non_constant_p = true;
}
FOR_EACH_VEC_ELT (global_ctx.heap_vars, i, heap_var)
- if (DECL_NAME (heap_var) != heap_deleted_identifier)
- {
- if (!allow_non_constant && !non_constant_p)
- error_at (DECL_SOURCE_LOCATION (heap_var),
- "%qE is not a constant expression because allocated "
- "storage has not been deallocated", t);
- r = t;
- non_constant_p = true;
- }
+ {
+ if (DECL_NAME (heap_var) != heap_deleted_identifier)
+ {
+ if (!allow_non_constant && !non_constant_p)
+ error_at (DECL_SOURCE_LOCATION (heap_var),
+ "%qE is not a constant expression because allocated "
+ "storage has not been deallocated", t);
+ r = t;
+ non_constant_p = true;
+ }
+ varpool_node::get (heap_var)->remove ();
+ }
}
/* Check that immediate invocation does not return an expression referencing
--- gcc/testsuite/g++.dg/cpp2a/constexpr-new16.C.jj 2021-02-10
11:11:00.117658382 +0100
+++ gcc/testsuite/g++.dg/cpp2a/constexpr-new16.C 2021-02-10
11:11:00.117658382 +0100
@@ -0,0 +1,13 @@
+// PR c++/98988
+// { dg-do compile { target c++20 } }
+// { dg-options "-fno-delete-null-pointer-checks" }
+
+constexpr bool
+foo ()
+{
+ auto ptr = new int();
+ delete ptr;
+ return true;
+}
+
+static_assert (foo ());
--- gcc/testsuite/g++.dg/cpp2a/constexpr-new17.C.jj 2021-02-10
13:04:17.947606440 +0100
+++ gcc/testsuite/g++.dg/cpp2a/constexpr-new17.C 2021-02-10
13:04:06.417738050 +0100
@@ -0,0 +1,15 @@
+// PR c++/99031
+// { dg-do compile { target c++20 } }
+
+constexpr bool
+foo ()
+{
+ auto a = new int;
+ auto b = new int;
+ bool r = a == b;
+ delete b;
+ delete a;
+ return r;
+}
+
+static_assert (!foo ());
Jakub
