[PATCH] Add a new type attribute always_alias (PR79671)
Richard Biener
rguenther@suse.de
Tue Apr 11 10:32:00 GMT 2017
On Mon, 10 Apr 2017, Jason Merrill wrote:
> On Mon, Apr 10, 2017 at 11:30 AM, Richard Biener <rguenther@suse.de> wrote:
> > On Mon, 10 Apr 2017, Jason Merrill wrote:
> >> On Mon, Apr 10, 2017 at 8:50 AM, Richard Biener <rguenther@suse.de> wrote:
> >> > * tree.c (build_cplus_array_type): Set TYPE_TYPELESS_STORAGE
> >> > for arrays of unsigned char or std::byte.
> >>
> >> I think it would be good to have a flag to select whether these
> >> semantics apply to any char variant and std::byte, only unsigned char
> >> and std::byte, or only std::byte.
> >
> > Any suggestion? Not sure we really need it (I'm hesitant to write
> > all the testcases to verify it actually works).
>
> Well, there's existing code that uses plain char (e.g. boost) that I
> want to support. If there's a significant optimization penalty for
> allowing that, we probably also want to be able to limit the impact.
> If there isn't much penalty, let's just support all char variants.
I haven't assessed the penalty involved but it can't be worse than
the situation we had in GCC 6. So I think it's reasonable to support
all char variants for now. One could add some instrumenting to
alias_set_subset_of / alias_sets_conflict_p but it would only yield
an upper bound on the number of failed queries (TBAA is a quite early
out before PTA info is used for example).
The following variant -- added missing
Index: gcc/cp/tree.c
===================================================================
--- gcc/cp/tree.c (revision 246832)
+++ gcc/cp/tree.c (working copy)
@@ -972,6 +979,7 @@ build_cplus_array_type (tree elt_type, t
as it will overwrite alignment etc. of all variants. */
TYPE_SIZE (t) = TYPE_SIZE (m);
TYPE_SIZE_UNIT (t) = TYPE_SIZE_UNIT (m);
+ TYPE_TYPELESS_STORAGE (t) = TYPE_TYPELESS_STORAGE (m);
}
TYPE_MAIN_VARIANT (t) = m;
that caused LTO bootstrap to fail and removed the tree-ssa-structalias.c
change (committed separately) [LTO] bootstrapped and tested ok on
x86_64-unknown-linux-gnu.
I've tested some template examples and they seem to work fine.
Ok for trunk?
Disclaimer: there might still be an issue with cross-language LTO
support, but it might at most result in TYPE_TYPELESS_STORAGE
getting lost. Trying to craft a testcase to verify my theory.
Thanks,
Richard.
2017-04-11 Richard Biener <rguenther@suse.de>
PR c++/79671
cp/
* tree.c (build_cplus_array_type): Set TYPE_TYPELESS_STORAGE
for arrays of unsigned char or std::byte.
* tree-core.h (tree_type_common): Add typeless_storage flag.
* tree.h (TYPE_TYPELESS_STORAGE): New macro.
(canonical_type_used_p): Add arrays with TYPE_TYPELESS_STORAGE.
* alias.c (alias_set_entry): Add has_typeless_storage member.
(alias_set_subset_of): Handle it.
(alias_sets_conflict_p): Likewise.
(init_alias_set_entry): Initialize it.
(get_alias_set): For ARRAY_TYPEs handle TYPE_TYPELESS_STORAGE.
(record_alias_subset): Likewise.
* lto-streamer-out.c (hash_tree): Hash TYPE_TYPELESS_STORAGE.
* tree-streamer-in.c (unpack_ts_type_common_value_fields): Stream
TYPE_TYPELESS_STORAGE.
* tree-streamer-out.c (pack_ts_type_common_value_fields): Likewise.
lto/
* lto.c (compare_tree_sccs_1): Compare TYPE_TYPELESS_STORAGE.
* g++.dg/torture/pr79671.C: New testcase.
Index: gcc/alias.c
===================================================================
--- gcc/alias.c (revision 246832)
+++ gcc/alias.c (working copy)
@@ -136,6 +136,9 @@ struct GTY(()) alias_set_entry {
bool is_pointer;
/* Nonzero if is_pointer or if one of childs have has_pointer set. */
bool has_pointer;
+ /* Nonzero if we have a child serving as typeless storage (or are
+ such storage ourselves). */
+ bool has_typeless_storage;
/* The children of the alias set. These are not just the immediate
children, but, in fact, all descendants. So, if we have:
@@ -419,7 +422,8 @@ alias_set_subset_of (alias_set_type set1
/* Check if set1 is a subset of set2. */
ase2 = get_alias_set_entry (set2);
if (ase2 != 0
- && (ase2->has_zero_child
+ && (ase2->has_typeless_storage
+ || ase2->has_zero_child
|| (ase2->children && ase2->children->get (set1))))
return true;
@@ -480,7 +484,8 @@ alias_sets_conflict_p (alias_set_type se
/* See if the first alias set is a subset of the second. */
ase1 = get_alias_set_entry (set1);
if (ase1 != 0
- && ase1->children && ase1->children->get (set2))
+ && (ase1->has_typeless_storage
+ || (ase1->children && ase1->children->get (set2))))
{
++alias_stats.num_dag;
return 1;
@@ -489,7 +494,8 @@ alias_sets_conflict_p (alias_set_type se
/* Now do the same, but with the alias sets reversed. */
ase2 = get_alias_set_entry (set2);
if (ase2 != 0
- && ase2->children && ase2->children->get (set1))
+ && (ase2->has_typeless_storage
+ || (ase2->children && ase2->children->get (set1))))
{
++alias_stats.num_dag;
return 1;
@@ -825,6 +831,7 @@ init_alias_set_entry (alias_set_type set
ase->has_zero_child = false;
ase->is_pointer = false;
ase->has_pointer = false;
+ ase->has_typeless_storage = false;
gcc_checking_assert (!get_alias_set_entry (set));
(*alias_sets)[set] = ase;
return ase;
@@ -955,6 +962,7 @@ get_alias_set (tree t)
Just be pragmatic here and make sure the array and its element
type get the same alias set assigned. */
else if (TREE_CODE (t) == ARRAY_TYPE
+ && ! TYPE_TYPELESS_STORAGE (t)
&& (!TYPE_NONALIASED_COMPONENT (t)
|| TYPE_STRUCTURAL_EQUALITY_P (t)))
set = get_alias_set (TREE_TYPE (t));
@@ -1094,6 +1102,15 @@ get_alias_set (tree t)
TYPE_ALIAS_SET (t) = set;
+ if (TREE_CODE (t) == ARRAY_TYPE
+ && TYPE_TYPELESS_STORAGE (t))
+ {
+ alias_set_entry *ase = get_alias_set_entry (set);
+ if (!ase)
+ ase = init_alias_set_entry (set);
+ ase->has_typeless_storage = true;
+ }
+
/* If this is an aggregate type or a complex type, we must record any
component aliasing information. */
if (AGGREGATE_TYPE_P (t) || TREE_CODE (t) == COMPLEX_TYPE)
@@ -1173,6 +1190,8 @@ record_alias_subset (alias_set_type supe
superset_entry->has_zero_child = true;
if (subset_entry->has_pointer)
superset_entry->has_pointer = true;
+ if (subset_entry->has_typeless_storage)
+ superset_entry->has_typeless_storage = true;
if (subset_entry->children)
{
Index: gcc/cp/tree.c
===================================================================
--- gcc/cp/tree.c (revision 246832)
+++ gcc/cp/tree.c (working copy)
@@ -949,6 +949,13 @@ build_cplus_array_type (tree elt_type, t
else
{
t = build_array_type (elt_type, index_type);
+ if (elt_type == unsigned_char_type_node
+ || elt_type == signed_char_type_node
+ || elt_type == char_type_node
+ || (TREE_CODE (elt_type) == ENUMERAL_TYPE
+ && TYPE_CONTEXT (elt_type) == std_node
+ && !strcmp ("byte", TYPE_NAME_STRING (elt_type))))
+ TYPE_TYPELESS_STORAGE (t) = 1;
}
/* Now check whether we already have this array variant. */
@@ -972,6 +979,7 @@ build_cplus_array_type (tree elt_type, t
as it will overwrite alignment etc. of all variants. */
TYPE_SIZE (t) = TYPE_SIZE (m);
TYPE_SIZE_UNIT (t) = TYPE_SIZE_UNIT (m);
+ TYPE_TYPELESS_STORAGE (t) = TYPE_TYPELESS_STORAGE (m);
}
TYPE_MAIN_VARIANT (t) = m;
Index: gcc/lto/lto.c
===================================================================
--- gcc/lto/lto.c (revision 246832)
+++ gcc/lto/lto.c (working copy)
@@ -1161,7 +1161,10 @@ compare_tree_sccs_1 (tree t1, tree t2, t
compare_values (TYPE_FINAL_P);
}
else if (code == ARRAY_TYPE)
- compare_values (TYPE_NONALIASED_COMPONENT);
+ {
+ compare_values (TYPE_NONALIASED_COMPONENT);
+ compare_values (TYPE_TYPELESS_STORAGE);
+ }
compare_values (TYPE_PACKED);
compare_values (TYPE_RESTRICT);
compare_values (TYPE_USER_ALIGN);
Index: gcc/lto-streamer-out.c
===================================================================
--- gcc/lto-streamer-out.c (revision 246832)
+++ gcc/lto-streamer-out.c (working copy)
@@ -1142,7 +1142,10 @@ hash_tree (struct streamer_tree_cache_d
hstate.add_flag (TYPE_FINAL_P (t));
}
else if (code == ARRAY_TYPE)
- hstate.add_flag (TYPE_NONALIASED_COMPONENT (t));
+ {
+ hstate.add_flag (TYPE_NONALIASED_COMPONENT (t));
+ hstate.add_flag (TYPE_TYPELESS_STORAGE (t));
+ }
hstate.commit_flag ();
hstate.add_int (TYPE_PRECISION (t));
hstate.add_int (TYPE_ALIGN (t));
Index: gcc/testsuite/g++.dg/torture/pr79671.C
===================================================================
--- gcc/testsuite/g++.dg/torture/pr79671.C (nonexistent)
+++ gcc/testsuite/g++.dg/torture/pr79671.C (working copy)
@@ -0,0 +1,25 @@
+// { dg-do run }
+
+void *operator new(__SIZE_TYPE__, void *p2) { return p2; }
+struct B { B(int i_) : i(i_) {} int i; };
+struct X
+{
+ unsigned char buf[sizeof (B)];
+};
+
+int __attribute__((noinline)) foo()
+{
+ X x alignas(B), y alignas(B);
+ new (&x) B (0);
+ y = x;
+ B *q = reinterpret_cast <B *>(&y);
+ asm volatile ("" : "=r" (q) : "r" (q));
+ return q->i;
+}
+
+int main()
+{
+ if (foo() != 0)
+ __builtin_abort ();
+ return 0;
+}
Index: gcc/tree-core.h
===================================================================
--- gcc/tree-core.h (revision 246832)
+++ gcc/tree-core.h (working copy)
@@ -1511,7 +1511,9 @@ struct GTY(()) tree_type_common {
so we need to store the value 32 (not 31, as we need the zero
as well), hence six bits. */
unsigned align : 6;
- unsigned spare : 25;
+ unsigned typeless_storage : 1;
+ unsigned spare : 24;
+
alias_set_type alias_set;
tree pointer_to;
tree reference_to;
Index: gcc/tree-streamer-in.c
===================================================================
--- gcc/tree-streamer-in.c (revision 246832)
+++ gcc/tree-streamer-in.c (working copy)
@@ -375,7 +375,10 @@ unpack_ts_type_common_value_fields (stru
TYPE_FINAL_P (expr) = (unsigned) bp_unpack_value (bp, 1);
}
else if (TREE_CODE (expr) == ARRAY_TYPE)
- TYPE_NONALIASED_COMPONENT (expr) = (unsigned) bp_unpack_value (bp, 1);
+ {
+ TYPE_NONALIASED_COMPONENT (expr) = (unsigned) bp_unpack_value (bp, 1);
+ TYPE_TYPELESS_STORAGE (expr) = (unsigned) bp_unpack_value (bp, 1);
+ }
TYPE_PRECISION (expr) = bp_unpack_var_len_unsigned (bp);
SET_TYPE_ALIGN (expr, bp_unpack_var_len_unsigned (bp));
#ifdef ACCEL_COMPILER
Index: gcc/tree-streamer-out.c
===================================================================
--- gcc/tree-streamer-out.c (revision 246832)
+++ gcc/tree-streamer-out.c (working copy)
@@ -327,7 +327,10 @@ pack_ts_type_common_value_fields (struct
bp_pack_value (bp, TYPE_FINAL_P (expr), 1);
}
else if (TREE_CODE (expr) == ARRAY_TYPE)
- bp_pack_value (bp, TYPE_NONALIASED_COMPONENT (expr), 1);
+ {
+ bp_pack_value (bp, TYPE_NONALIASED_COMPONENT (expr), 1);
+ bp_pack_value (bp, TYPE_TYPELESS_STORAGE (expr), 1);
+ }
bp_pack_var_len_unsigned (bp, TYPE_PRECISION (expr));
bp_pack_var_len_unsigned (bp, TYPE_ALIGN (expr));
}
Index: gcc/tree.h
===================================================================
--- gcc/tree.h (revision 246832)
+++ gcc/tree.h (working copy)
@@ -2035,6 +2035,9 @@ extern machine_mode element_mode (const_
#define TYPE_NONALIASED_COMPONENT(NODE) \
(ARRAY_TYPE_CHECK (NODE)->type_common.transparent_aggr_flag)
+#define TYPE_TYPELESS_STORAGE(NODE) \
+ (ARRAY_TYPE_CHECK (NODE)->type_common.typeless_storage)
+
/* Indicated that objects of this type should be laid out in as
compact a way as possible. */
#define TYPE_PACKED(NODE) (TYPE_CHECK (NODE)->base.u.bits.packed_flag)
@@ -4914,7 +4917,7 @@ inline bool
canonical_type_used_p (const_tree t)
{
return !(POINTER_TYPE_P (t)
- || TREE_CODE (t) == ARRAY_TYPE
+ || (TREE_CODE (t) == ARRAY_TYPE && ! TYPE_TYPELESS_STORAGE (t))
|| TREE_CODE (t) == VECTOR_TYPE);
}
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