On Fri, Mar 11, 2016 at 09:27:54AM -0500, Jason Merrill wrote:
> On 03/10/2016 01:39 PM, Jakub Jelinek wrote:
> >+ /* Don't reuse the result of cxx_eval_constant_expression
> >+ call if it isn't a constant initializer or if it requires
> >+ relocations. */
>
> Let's phrase this positively ("Reuse the result if...").
>
> >+ if (new_ctx.ctor != ctx->ctor)
> >+ eltinit = new_ctx.ctor;
> >+ for (i = 1; i < max; ++i)
> >+ {
> >+ idx = build_int_cst (size_type_node, i);
> >+ CONSTRUCTOR_APPEND_ELT (*p, idx, eltinit);
> >+ }
>
> This is going to use the same CONSTRUCTOR for all the elements, which will
> lead to problems if we then store into a subobject of one of the elements
> and see that reflected in all the others as well. We need to unshare_expr
> when reusing the initializer.
Ok, here is a new version with unshare_expr and reworded comment.
I haven't been successful with writing a testcase where the unshare_expr
would matter, but have included what I've tried in the patch anyway.
Compile-time wise the unshare_expr is not very costly, and e.g. for the
other testcase in this patch gives a nice compile time speedup.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2016-03-11 Jakub Jelinek <ja...@redhat.com>
PR c++/70001
* constexpr.c (cxx_eval_vec_init_1): Reuse CONSTRUCTOR initializers
for 1..max even for multi-dimensional arrays. Call unshare_expr
on it.
* g++.dg/cpp0x/constexpr-70001-4.C: New test.
* g++.dg/cpp1y/pr70001.C: New test.
--- gcc/cp/constexpr.c.jj 2016-03-10 12:52:04.000000000 +0100
+++ gcc/cp/constexpr.c 2016-03-11 19:24:28.435537864 +0100
@@ -2340,7 +2340,6 @@ cxx_eval_vec_init_1 (const constexpr_ctx
vec<constructor_elt, va_gc> **p = &CONSTRUCTOR_ELTS (ctx->ctor);
vec_alloc (*p, max + 1);
bool pre_init = false;
- tree pre_init_elt = NULL_TREE;
unsigned HOST_WIDE_INT i;
/* For the default constructor, build up a call to the default
@@ -2370,6 +2369,7 @@ cxx_eval_vec_init_1 (const constexpr_ctx
{
tree idx = build_int_cst (size_type_node, i);
tree eltinit;
+ bool reuse = false;
constexpr_ctx new_ctx;
init_subob_ctx (ctx, new_ctx, idx, pre_init ? init : elttype);
if (new_ctx.ctor != ctx->ctor)
@@ -2378,7 +2378,10 @@ cxx_eval_vec_init_1 (const constexpr_ctx
{
/* A multidimensional array; recurse. */
if (value_init || init == NULL_TREE)
- eltinit = NULL_TREE;
+ {
+ eltinit = NULL_TREE;
+ reuse = i == 0;
+ }
else
eltinit = cp_build_array_ref (input_location, init, idx,
tf_warning_or_error);
@@ -2390,18 +2393,9 @@ cxx_eval_vec_init_1 (const constexpr_ctx
{
/* Initializing an element using value or default initialization
we just pre-built above. */
- if (pre_init_elt == NULL_TREE)
- pre_init_elt
- = cxx_eval_constant_expression (&new_ctx, init, lval,
- non_constant_p, overflow_p);
- eltinit = pre_init_elt;
- /* Don't reuse the result of cxx_eval_constant_expression
- call if it isn't a constant initializer or if it requires
- relocations. */
- if (initializer_constant_valid_p (pre_init_elt,
- TREE_TYPE (pre_init_elt))
- != null_pointer_node)
- pre_init_elt = NULL_TREE;
+ eltinit = cxx_eval_constant_expression (&new_ctx, init, lval,
+ non_constant_p, overflow_p);
+ reuse = i == 0;
}
else
{
@@ -2427,6 +2421,23 @@ cxx_eval_vec_init_1 (const constexpr_ctx
}
else
CONSTRUCTOR_APPEND_ELT (*p, idx, eltinit);
+ /* Reuse the result of cxx_eval_constant_expression call
+ from the first iteration to all others if it is a constant
+ initializer that doesn't require relocations. */
+ if (reuse
+ && max > 1
+ && (initializer_constant_valid_p (eltinit, TREE_TYPE (eltinit))
+ == null_pointer_node))
+ {
+ if (new_ctx.ctor != ctx->ctor)
+ eltinit = new_ctx.ctor;
+ for (i = 1; i < max; ++i)
+ {
+ idx = build_int_cst (size_type_node, i);
+ CONSTRUCTOR_APPEND_ELT (*p, idx, unshare_expr (eltinit));
+ }
+ break;
+ }
}
if (!*non_constant_p)
--- gcc/testsuite/g++.dg/cpp0x/constexpr-70001-4.C.jj 2016-03-10
19:28:13.386481311 +0100
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-70001-4.C 2016-03-10
19:28:43.295074924 +0100
@@ -0,0 +1,13 @@
+// PR c++/70001
+// { dg-do compile { target c++11 } }
+
+struct B
+{
+ int a;
+ constexpr B () : a (0) { }
+};
+
+struct A
+{
+ B b[1 << 19][1][1][1];
+} c;
--- gcc/testsuite/g++.dg/cpp1y/pr70001.C.jj 2016-03-11 18:22:15.526046513
+0100
+++ gcc/testsuite/g++.dg/cpp1y/pr70001.C 2016-03-11 18:21:43.000000000
+0100
@@ -0,0 +1,49 @@
+// PR c++/70001
+// { dg-do compile { target c++14 } }
+
+struct B
+{
+ int a;
+ constexpr B () : a (0) { }
+ constexpr B (int x) : a (x) { }
+};
+struct C
+{
+ B c;
+ constexpr C () : c (0) { }
+};
+struct A
+{
+ B b[1 << 4];
+};
+struct D
+{
+ C d[1 << 4];
+};
+
+constexpr int
+foo (int a, int b)
+{
+ A c;
+ c.b[a].a += b;
+ c.b[b].a += a;
+ return c.b[0].a + c.b[a].a + c.b[b].a;
+}
+
+constexpr int
+bar (int a, int b)
+{
+ D c;
+ c.d[a].c.a += b;
+ c.d[b].c.a += a;
+ return c.d[0].c.a + c.d[a].c.a + c.d[b].c.a;
+}
+
+constexpr int d = foo (1, 2);
+constexpr int e = foo (0, 3);
+constexpr int f = foo (2, 4);
+constexpr int g = bar (1, 2);
+constexpr int h = bar (0, 3);
+constexpr int i = bar (2, 4);
+static_assert (d == 3 && e == 6 && f == 6, "");
+static_assert (g == 3 && h == 6 && i == 6, "");
Jakub
