* [C++/66270] another may_alias crash
@ 2015-05-25 21:09 Nathan Sidwell
2015-05-26 7:52 ` Jason Merrill
0 siblings, 1 reply; 6+ messages in thread
From: Nathan Sidwell @ 2015-05-25 21:09 UTC (permalink / raw)
To: Jason Merrill, GCC Patches
[-- Attachment #1: Type: text/plain, Size: 1798 bytes --]
This patch addresses 66270, another case where may_alias disrupted the canonical
type system. We ICE as TYPE_CANONICALs differ, but comptypes think they are the
same.
There seems to be a bit of confusion as to whether pointers that differ only in
TYPE_REF_CAN_ALIAS_ALL are the same canonical type or not.
Firstly, in tree.c build_pointer_type_for_mode, when the pointed-to type is not
its own canonical type, that means the newly constructed pointer type is
(possibly) not canonical either. So we explicitly build a canonical type with:
else if (TYPE_CANONICAL (to_type) != to_type)
TYPE_CANONICAL (t)
= build_reference_type_for_mode (TYPE_CANONICAL (to_type),
mode, false);
But we're passing 'false' in as 'can_alias_all', rather than pass the value
passed into us. That'll make a difference if the caller passed in true and
to_type doesn't have may_alias set. This is inconsistent at least, because we
could sometimes end up with canonical types with T_R_C_A_A set (to-type is
canonical) and sometimes with it not set. It seems the right solution is to
consider T_R_C_A_A as a distinguisher, thus we should pass can_alias_all to the
canonical type builder. Note that it is ok to pass the possibly modified
can_alias_all in, and not the incoming value, because we only ever modify it to
make it true -- and in that case the same behavior would happen in the canonical
type builder because to_type and TYPE_CANONICAL (to_type) should have the same
may_alias attribute.
Anyway, that's a bit of collateral confusion I fell over investigating. With
that out of the way, we have to teach comptypes that T_R_C_A_A affects pointer
type equality. Hence add such a check to POINTER_TYPE case there.
bootstrapped on x86-linux & tested, ok?
nathan
[-- Attachment #2: 66270.patch --]
[-- Type: text/x-patch, Size: 2077 bytes --]
2015-05-25 Nathan Sidwell <nathan@acm.org>
PR c++/66270
* tree.c (build_pointer_type_for_mode): Pass can_alias_all to
canonical type builder.
(build_reference_type_for_mode): Likewise.
cp/
* typeck.c (structural_comptypes) [POINTER_TYPE]: Compare
TYPE_REF_CAN_ALIAS_ALL.
testsuite/
* g++.dg/ext/alias-canon3.C: New.
Index: cp/typeck.c
===================================================================
--- cp/typeck.c (revision 223636)
+++ cp/typeck.c (working copy)
@@ -1307,6 +1307,8 @@ structural_comptypes (tree t1, tree t2,
if (TYPE_MODE (t1) != TYPE_MODE (t2)
|| !same_type_p (TREE_TYPE (t1), TREE_TYPE (t2)))
return false;
+ if (TYPE_REF_CAN_ALIAS_ALL (t1) != TYPE_REF_CAN_ALIAS_ALL (t2))
+ return false;
break;
case METHOD_TYPE:
Index: tree.c
===================================================================
--- tree.c (revision 223636)
+++ tree.c (working copy)
@@ -7759,7 +7759,7 @@ build_pointer_type_for_mode (tree to_typ
else if (TYPE_CANONICAL (to_type) != to_type)
TYPE_CANONICAL (t)
= build_pointer_type_for_mode (TYPE_CANONICAL (to_type),
- mode, false);
+ mode, can_alias_all);
/* Lay out the type. This function has many callers that are concerned
with expression-construction, and this simplifies them all. */
@@ -7826,7 +7826,7 @@ build_reference_type_for_mode (tree to_t
else if (TYPE_CANONICAL (to_type) != to_type)
TYPE_CANONICAL (t)
= build_reference_type_for_mode (TYPE_CANONICAL (to_type),
- mode, false);
+ mode, can_alias_all);
layout_type (t);
Index: testsuite/g++.dg/ext/alias-canon3.C
===================================================================
--- testsuite/g++.dg/ext/alias-canon3.C (revision 0)
+++ testsuite/g++.dg/ext/alias-canon3.C (working copy)
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// PR c++/66270
+
+typedef float __m256 __attribute__ (( __vector_size__(32), __may_alias__ ));
+struct A {
+ __m256 ymm;
+ const float &f() const;
+};
+
+const float &A::f() const {
+ return ymm[1];
+}
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++/66270] another may_alias crash
2015-05-25 21:09 [C++/66270] another may_alias crash Nathan Sidwell
@ 2015-05-26 7:52 ` Jason Merrill
2015-05-26 19:18 ` Nathan Sidwell
0 siblings, 1 reply; 6+ messages in thread
From: Jason Merrill @ 2015-05-26 7:52 UTC (permalink / raw)
To: Nathan Sidwell, GCC Patches
On 05/25/2015 04:55 PM, Nathan Sidwell wrote:
> This patch addresses 66270, another case where may_alias disrupted the
> canonical type system. We ICE as TYPE_CANONICALs differ, but comptypes
> think they are the same.
>
> There seems to be a bit of confusion as to whether pointers that differ
> only in TYPE_REF_CAN_ALIAS_ALL are the same canonical type or not.
>
> Firstly, in tree.c build_pointer_type_for_mode, when the pointed-to type
> is not its own canonical type, that means the newly constructed pointer
> type is (possibly) not canonical either. So we explicitly build a
> canonical type with:
>
> else if (TYPE_CANONICAL (to_type) != to_type)
> TYPE_CANONICAL (t)
> = build_reference_type_for_mode (TYPE_CANONICAL (to_type),
> mode, false);
>
> But we're passing 'false' in as 'can_alias_all', rather than pass the
> value passed into us.
Yes, I actually just changed that a month ago because we were hitting
this same ICE from a different direction (bug 50800). Since
TYPE_CANONICAL (to_type) doesn't have the may_alias attribute, the
canonical pointer shouldn't have TRCAA.
> That'll make a difference if the caller passed in
> true and to_type doesn't have may_alias set. This is inconsistent at
> least, because we could sometimes end up with canonical types with
> T_R_C_A_A set (to-type is canonical) and sometimes with it not set. It
> seems the right solution is to consider T_R_C_A_A as a distinguisher,
> thus we should pass can_alias_all to the canonical type builder. Note
> that it is ok to pass the possibly modified can_alias_all in, and not
> the incoming value, because we only ever modify it to make it true --
> and in that case the same behavior would happen in the canonical type
> builder because to_type and TYPE_CANONICAL (to_type) should have the
> same may_alias attribute.
Hmm, are you seeing a case where TYPE_CANONICAL (to_type) has the
may_alias attribute?
> Anyway, that's a bit of collateral confusion I fell over investigating.
> With that out of the way, we have to teach comptypes that T_R_C_A_A
> affects pointer type equality. Hence add such a check to POINTER_TYPE
> case there.
Similarly, I removed this check for bug 50800.
Jason
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++/66270] another may_alias crash
2015-05-26 7:52 ` Jason Merrill
@ 2015-05-26 19:18 ` Nathan Sidwell
2015-05-27 12:42 ` Nathan Sidwell
2015-05-27 16:36 ` Jason Merrill
0 siblings, 2 replies; 6+ messages in thread
From: Nathan Sidwell @ 2015-05-26 19:18 UTC (permalink / raw)
To: Jason Merrill, GCC Patches
On 05/25/15 21:18, Jason Merrill wrote:
> On 05/25/2015 04:55 PM, Nathan Sidwell wrote:
>> else if (TYPE_CANONICAL (to_type) != to_type)
>> TYPE_CANONICAL (t)
>> = build_reference_type_for_mode (TYPE_CANONICAL (to_type),
>> mode, false);
>>
>> But we're passing 'false' in as 'can_alias_all', rather than pass the
>> value passed into us.
>
> Yes, I actually just changed that a month ago because we were hitting this same
> ICE from a different direction (bug 50800). Since TYPE_CANONICAL (to_type)
> doesn't have the may_alias attribute, the canonical pointer shouldn't have TRCAA.
Ok, so IIUC a canonical pointer to a may_alias type should have TRCAA but a
canonical can_alias_all pointer to a non-may_alias type should not have TRCAA?
(i.e. one where CAN_ALIAS_ALL was passed true). Or are you saying that no
canonical pointers should have TRCAA?
> Hmm, are you seeing a case where TYPE_CANONICAL (to_type) has the may_alias
> attribute?
Yes. This occurs when the newly created TRCAA pointer is to a self-canonical
type. The
else if (TYPE_CANONICAL (to_type) != to_type)
is false, so the newly created pointer is self-canonical too (and has TRCAA).
If the canonical type should not have TRCAA we need to change the if condition to:
else if (TYPE_CANONICAL (to_type) != to_type || could_alias_all)
where COULD_ALIAS_ALL is the incoming CAN_ALIAS_ALL value. Does that make sense?
Making that change does stop the ICE I was seeing, but I've not done a full
test yet.
nathan
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++/66270] another may_alias crash
2015-05-26 19:18 ` Nathan Sidwell
@ 2015-05-27 12:42 ` Nathan Sidwell
2015-05-27 16:36 ` Jason Merrill
1 sibling, 0 replies; 6+ messages in thread
From: Nathan Sidwell @ 2015-05-27 12:42 UTC (permalink / raw)
To: Jason Merrill, GCC Patches
[-- Attachment #1: Type: text/plain, Size: 987 bytes --]
On 05/26/15 15:00, Nathan Sidwell wrote:
> On 05/25/15 21:18, Jason Merrill wrote:
>> Hmm, are you seeing a case where TYPE_CANONICAL (to_type) has the may_alias
>> attribute?
>
> Yes. This occurs when the newly created TRCAA pointer is to a self-canonical
> type. The
> else if (TYPE_CANONICAL (to_type) != to_type)
> is false, so the newly created pointer is self-canonical too (and has TRCAA).
>
> If the canonical type should not have TRCAA we need to change the if condition to:
> else if (TYPE_CANONICAL (to_type) != to_type || could_alias_all)
>
> where COULD_ALIAS_ALL is the incoming CAN_ALIAS_ALL value. Does that make sense?
>
> Making that change does stop the ICE I was seeing, but I've not done a full
> test yet.
Here's a patch implementing that change, When build_pointer_type_for_mode is
passed true for CAN_ALIAS_ALL, we force creating a canonical type, continuing to
pass false for that pointer's creation.
booted & tested on x86-64-linux, ok?
nathan
[-- Attachment #2: 66270-2.patch --]
[-- Type: text/x-patch, Size: 2018 bytes --]
2015-05-25 Nathan Sidwell <nathan@acm.org>
PR c++/66270
* tree.c (build_pointer_type_for_mode): Canonical type does not
inherit can_alias_all.
(build_reference_type_for_mode): Likewise.
PR c++/66270
* g++.dg/ext/alias-canon3.C: New.
Index: testsuite/g++.dg/ext/alias-canon3.C
===================================================================
--- testsuite/g++.dg/ext/alias-canon3.C (revision 0)
+++ testsuite/g++.dg/ext/alias-canon3.C (working copy)
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// PR c++/66270
+
+typedef float __m256 __attribute__ (( __vector_size__(32), __may_alias__ ));
+struct A {
+ __m256 ymm;
+ const float &f() const;
+};
+
+const float &A::f() const {
+ return ymm[1];
+}
Index: tree.c
===================================================================
--- tree.c (revision 223636)
+++ tree.c (working copy)
@@ -7719,6 +7719,7 @@ build_pointer_type_for_mode (tree to_typ
bool can_alias_all)
{
tree t;
+ bool could_alias = can_alias_all;
if (to_type == error_mark_node)
return error_mark_node;
@@ -7756,7 +7757,7 @@ build_pointer_type_for_mode (tree to_typ
if (TYPE_STRUCTURAL_EQUALITY_P (to_type))
SET_TYPE_STRUCTURAL_EQUALITY (t);
- else if (TYPE_CANONICAL (to_type) != to_type)
+ else if (TYPE_CANONICAL (to_type) != to_type || could_alias)
TYPE_CANONICAL (t)
= build_pointer_type_for_mode (TYPE_CANONICAL (to_type),
mode, false);
@@ -7786,6 +7787,7 @@ build_reference_type_for_mode (tree to_t
bool can_alias_all)
{
tree t;
+ bool could_alias = can_alias_all;
if (to_type == error_mark_node)
return error_mark_node;
@@ -7823,7 +7825,7 @@ build_reference_type_for_mode (tree to_t
if (TYPE_STRUCTURAL_EQUALITY_P (to_type))
SET_TYPE_STRUCTURAL_EQUALITY (t);
- else if (TYPE_CANONICAL (to_type) != to_type)
+ else if (TYPE_CANONICAL (to_type) != to_type || could_alias)
TYPE_CANONICAL (t)
= build_reference_type_for_mode (TYPE_CANONICAL (to_type),
mode, false);
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++/66270] another may_alias crash
2015-05-26 19:18 ` Nathan Sidwell
2015-05-27 12:42 ` Nathan Sidwell
@ 2015-05-27 16:36 ` Jason Merrill
2015-05-27 21:26 ` Nathan Sidwell
1 sibling, 1 reply; 6+ messages in thread
From: Jason Merrill @ 2015-05-27 16:36 UTC (permalink / raw)
To: Nathan Sidwell, GCC Patches
On 05/26/2015 03:00 PM, Nathan Sidwell wrote:
> Ok, so IIUC a canonical pointer to a may_alias type should have TRCAA
> but a canonical can_alias_all pointer to a non-may_alias type should not
> have TRCAA? (i.e. one where CAN_ALIAS_ALL was passed true). Or are you
> saying that no canonical pointers should have TRCAA?
The former: A canonical pointer should have TRCAA if and only if the
canonical referent is may_alias.
>> Hmm, are you seeing a case where TYPE_CANONICAL (to_type) has the
>> may_alias attribute?
>
> Yes. This occurs when the newly created TRCAA pointer is to a
> self-canonical type.
Hmm, seems like that's another problem with your testcase: the canonical
variant of __m256 should not have may_alias. But the canonical variant
of a class or enum type could still have may_alias, so we still need to
handle that case.
The patch is OK.
Jason
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [C++/66270] another may_alias crash
2015-05-27 16:36 ` Jason Merrill
@ 2015-05-27 21:26 ` Nathan Sidwell
0 siblings, 0 replies; 6+ messages in thread
From: Nathan Sidwell @ 2015-05-27 21:26 UTC (permalink / raw)
To: Jason Merrill, GCC Patches
On 05/27/15 12:20, Jason Merrill wrote:
> On 05/26/2015 03:00 PM, Nathan Sidwell wrote:
>> Ok, so IIUC a canonical pointer to a may_alias type should have TRCAA
>> but a canonical can_alias_all pointer to a non-may_alias type should not
>> have TRCAA? (i.e. one where CAN_ALIAS_ALL was passed true). Or are you
>> saying that no canonical pointers should have TRCAA?
>
> The former: A canonical pointer should have TRCAA if and only if the canonical
> referent is may_alias.
>
>>> Hmm, are you seeing a case where TYPE_CANONICAL (to_type) has the
>>> may_alias attribute?
>>
>> Yes. This occurs when the newly created TRCAA pointer is to a
>> self-canonical type.
>
> Hmm, seems like that's another problem with your testcase: the canonical variant
> of __m256 should not have may_alias. But the canonical variant of a class or
> enum type could still have may_alias, so we still need to handle that case.
I was unclear in my description. The canonical pointer type was being created
with TRCAA set because of the incoming true CAN_ALIAS_ALL parameter. That's
fixed by the patch, so we're all good now.
nathan
^ permalink raw reply [flat|nested] 6+ messages in thread
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2015-05-25 21:09 [C++/66270] another may_alias crash Nathan Sidwell
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