On Wed, 27 May 2020, Patrick Palka wrote:
> On Wed, 27 May 2020, Patrick Palka wrote:
>
> > In the testcase below, the CONSTRUCTOR for 'field' contains a
> > RANGE_EXPR index:
> >
> > {aggr_init_expr<...>, [1...2]={.off=1}}
> >
> > but get_or_insert_ctor_field isn't prepared to handle RANGE_EXPR
> > indexes.
> >
> > This patch adds limited support for RANGE_EXPR indexes to
> > get_or_insert_ctor_field. The limited scope of this patch should make
> > it more suitable for backporting, and support for more access patterns
> > would be needed only to handle self-modifying CONSTRUCTORs containing a
> > RANGE_EXPR index, but I haven't yet been able to come up with a testcase
> > that exhibits such a CONSTRUCTOR.
> >
> > Passes 'make check-c++', does this look OK to commit to master and to
> > the GCC 10 branch after a full bootstrap and regtest?
> >
> > gcc/cp/ChangeLog:
> >
> > PR c++/95241
> > * constexpr.c (get_or_insert_ctor_field): Add limited support
> > for RANGE_EXPR indexes.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR c++/95241
> > * g++.dg/cpp0x/constexpr-array25.C: New test.
> > ---
> > gcc/cp/constexpr.c | 12 +++++++++++
> > .../g++.dg/cpp0x/constexpr-array25.C | 21 +++++++++++++++++++
> > 2 files changed, 33 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-array25.C
> >
> > diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
> > index 4e441ac8d2f..6f9bafbe8d8 100644
> > --- a/gcc/cp/constexpr.c
> > +++ b/gcc/cp/constexpr.c
> > @@ -3301,6 +3301,18 @@ get_or_insert_ctor_field (tree ctor, tree index, int
> > pos_hint = -1)
> > }
> > else if (TREE_CODE (type) == ARRAY_TYPE || TREE_CODE (type) ==
> > VECTOR_TYPE)
> > {
> > + if (TREE_CODE (index) == RANGE_EXPR)
> > + {
> > + /* Our support for RANGE_EXPR indexes is limited to accessing an
> > + existing one via POS_HINT, and appending a new one to the end of
> > + CTOR. ??? Support for other access patterns might be needed. */
> > + tree lo = TREE_OPERAND (index, 0);
> > + auto *elts = CONSTRUCTOR_ELTS (ctor);
> > + gcc_assert (vec_safe_is_empty (elts)
> > + || array_index_cmp (lo, elts->last().index) > 0);
> > + return vec_safe_push (elts, {index, NULL_TREE});
> > + }
> > +
>
> Oops, it just occurred to me that the use of C++11 features here would
> make this patch unsuitable for backporting. C++98-compatible patch
> incoming...
Here it is. Does the following look OK to commit to master and to the
GCC 10 branch after a full bootstrap and regtest?
-- >8 --
Subject: [PATCH] c++: constexpr RANGE_EXPR ctor indexes [PR95241]
In the testcase below, the CONSTRUCTOR for 'field' contains a
RANGE_EXPR index:
{aggr_init_expr<...>, [1...2]={.off=1}}
but get_or_insert_ctor_field isn't prepared to handle RANGE_EXPR
indexes.
This patch adds limited support for RANGE_EXPR indexes to
get_or_insert_ctor_field. The limited scope of this patch should make
it more suitable for backporting, and support for more access patterns
would be needed only to handle self-modifying CONSTRUCTORs containing a
RANGE_EXPR index, but I haven't yet been able to come up with a testcase
that exhibits such a CONSTRUCTOR.
gcc/cp/ChangeLog:
PR c++/95241
* constexpr.c (get_or_insert_ctor_field): Add limited support
for RANGE_EXPR indexes.
gcc/testsuite/ChangeLog:
PR c++/95241
* g++.dg/cpp0x/constexpr-array25.C: New test.
---
gcc/cp/constexpr.c | 15 +++++++++++++
.../g++.dg/cpp0x/constexpr-array25.C | 21 +++++++++++++++++++
2 files changed, 36 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-array25.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 4e441ac8d2f..32f2ef96fc7 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -3301,6 +3301,21 @@ get_or_insert_ctor_field (tree ctor, tree index, int
pos_hint = -1)
}
else if (TREE_CODE (type) == ARRAY_TYPE || TREE_CODE (type) == VECTOR_TYPE)
{
+ if (TREE_CODE (index) == RANGE_EXPR)
+ {
+ /* ??? Support for RANGE_EXPR indexes is currently limited to
+ accessing one via POS_HINT, or appending a new one to the end
+ of CTOR. Support for other access patterns may be needed. */
+ vec<constructor_elt, va_gc> *elts = CONSTRUCTOR_ELTS (ctor);
+ if (vec_safe_length (elts))
+ {
+ tree lo = TREE_OPERAND (index, 0);
+ gcc_assert (array_index_cmp (lo, elts->last().index) > 0);
+ }
+ CONSTRUCTOR_APPEND_ELT (elts, index, NULL_TREE);
+ return &elts->last();
+ }
+
HOST_WIDE_INT i = find_array_ctor_elt (ctor, index, /*insert*/true);
gcc_assert (i >= 0);
constructor_elt *cep = CONSTRUCTOR_ELT (ctor, i);
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array25.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-array25.C
new file mode 100644
index 00000000000..9162943249f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array25.C
@@ -0,0 +1,21 @@
+// PR c++/95241
+// { dg-do compile { target c++11 } }
+
+struct Fragment
+{
+ int off;
+ constexpr Fragment(int _off) : off(_off) { }
+ constexpr Fragment() : Fragment(1) { }
+};
+
+struct Field
+{
+ Fragment fragments[3];
+ constexpr Field(int off) : fragments{{off}} { }
+};
+
+constexpr Field field{0};
+
+static_assert(field.fragments[0].off == 0
+ && field.fragments[1].off == 1
+ && field.fragments[2].off == 1, "");
--
2.27.0.rc1.5.gae92ac8ae3
