[PATCH, devirtualization] Detect the new type in type change detection
Richard Guenther
richard.guenther@gmail.com
Tue Nov 1 09:37:00 GMT 2011
On Mon, Oct 31, 2011 at 5:58 PM, Martin Jambor <mjambor@suse.cz> wrote:
> On Fri, Oct 28, 2011 at 11:21:23AM +0200, Richard Guenther wrote:
>> On Thu, Oct 27, 2011 at 9:54 PM, Martin Jambor <mjambor@suse.cz> wrote:
>> > Hi,
>> >
>> > On Thu, Oct 27, 2011 at 11:06:02AM +0200, Richard Guenther wrote:
>> >> On Thu, Oct 27, 2011 at 1:22 AM, Martin Jambor <mjambor@suse.cz> wrote:
>> >> > Hi,
>> >> >
>> >> > I've been asked by Maxim Kuvyrkov to revive the following patch which
>> >> > has not made it to 4.6. Currently, when type based devirtualization
>> >> > detects a potential type change, it simply gives up on gathering any
>> >> > information on the object in question. This patch adds an attempt to
>> >> > actually detect the new type after the change.
>> >> >
>> >> > Maxim claimed this (and another patch I'll post tomorrow) noticeably
>> >> > improved performance of some real code. I can only offer a rather
>> >> > artificial example in the attachment. When the constructors are
>> >> > inlined but the function multiply_matrices is not, this patch makes
>> >> > the produced executable run for only 7 seconds instead of about 20 on
>> >> > my 4 year old i686 desktop (with -Ofast).
>> >> >
>> >> > Anyway, the patch passes bootstrap and testsuite on x86_64-linux.
>> >> > What do you think, is it a good idea for trunk now?
>> >> >
>> >> > Thanks,
>> >> >
>> >> > Martin
>> >> >
>> >> >
>> >> > 2011-10-21 Martin Jambor <mjambor@suse.cz>
>> >> >
>> >> > * ipa-prop.c (type_change_info): New fields object, known_current_type
>> >> > and multiple_types_encountered.
>> >> > (extr_type_from_vtbl_ptr_store): New function.
>> >> > (check_stmt_for_type_change): Use it, set multiple_types_encountered if
>> >> > the result is different from the previous one.
>> >> > (detect_type_change): Renamed to detect_type_change_1. New parameter
>> >> > comp_type. Set up new fields in tci, build known type jump
>> >> > functions if the new type can be identified.
>> >> > (detect_type_change): New function.
>> >> > * tree.h (DECL_CONTEXT): Comment new use.
>> >> >
>> >> > * testsuite/g++.dg/ipa/devirt-c-1.C: Add dump scans.
>> >> > * testsuite/g++.dg/ipa/devirt-c-2.C: Likewise.
>> >> > * testsuite/g++.dg/ipa/devirt-c-7.C: New test.
>> >> >
>> >> >
>> >> > Index: src/gcc/ipa-prop.c
>> >> > ===================================================================
>> >> > --- src.orig/gcc/ipa-prop.c
>> >> > +++ src/gcc/ipa-prop.c
>> >> > @@ -271,8 +271,17 @@ ipa_print_all_jump_functions (FILE *f)
>> >> >
>> >> > struct type_change_info
>> >> > {
>> >> > + /* The declaration or SSA_NAME pointer of the base that we are checking for
>> >> > + type change. */
>> >> > + tree object;
>> >> > + /* If we actually can tell the type that the object has changed to, it is
>> >> > + stored in this field. Otherwise it remains NULL_TREE. */
>> >> > + tree known_current_type;
>> >> > /* Set to true if dynamic type change has been detected. */
>> >> > bool type_maybe_changed;
>> >> > + /* Set to true if multiple types have been encountered. known_current_type
>> >> > + must be disregarded in that case. */
>> >> > + bool multiple_types_encountered;
>> >> > };
>> >> >
>> >> > /* Return true if STMT can modify a virtual method table pointer.
>> >> > @@ -338,6 +347,49 @@ stmt_may_be_vtbl_ptr_store (gimple stmt)
>> >> > return true;
>> >> > }
>> >> >
>> >> > +/* If STMT can be proved to be an assignment to the virtual method table
>> >> > + pointer of ANALYZED_OBJ and the type associated with the new table
>> >> > + identified, return the type. Otherwise return NULL_TREE. */
>> >> > +
>> >> > +static tree
>> >> > +extr_type_from_vtbl_ptr_store (gimple stmt, tree analyzed_obj)
>> >> > +{
>> >> > + tree lhs, t, obj;
>> >> > +
>> >> > + if (!is_gimple_assign (stmt))
>> >>
>> >> gimple_assign_single_p (stmt)
>> >
>> > OK.
>> >
>> >>
>> >> > + return NULL_TREE;
>> >> > +
>> >> > + lhs = gimple_assign_lhs (stmt);
>> >> > +
>> >> > + if (TREE_CODE (lhs) != COMPONENT_REF)
>> >> > + return NULL_TREE;
>> >> > + obj = lhs;
>> >> > +
>> >> > + if (!DECL_VIRTUAL_P (TREE_OPERAND (lhs, 1)))
>> >> > + return NULL_TREE;
>> >> > +
>> >> > + do
>> >> > + {
>> >> > + obj = TREE_OPERAND (obj, 0);
>> >> > + }
>> >> > + while (TREE_CODE (obj) == COMPONENT_REF);
>> >>
>> >> You do not allow other components than component-refs (thus, for
>> >> example an ARRAY_REF - that is for a reason?). Please add
>> >> a comment why. Otherwise this whole sequence would look like
>> >> it should be replaceable by get_base_address (obj).
>> >>
>> >
>> > I guess I might have been overly conservative here, ARRAY_REFs are
>> > fine. get_base_address only digs into MEM_REFs if they are based on
>> > an ADDR_EXPR while I do so always. But I can check that either both
>> > obj and analyzed_obj are a MEM_REF of the same SSA_NAME or they are
>> > the same thing (i.e. the same decl)... which even feels a bit cleaner,
>> > so I did that.
>>
>> Well, as you are looking for a must-change-type pattern I think you cannot
>> simply ignore offsets. Consider
>>
>> T a[10];
>>
>> new (T') (&a[9]);
>> a[8]->foo();
>>
>> where the must-type-change on a[9] is _not_ changing the type of a[8]!
>>
>> Similar cases might happen with
>>
>> class Compound { T a; T b; };
>>
>> no?
>>
>> Please think about the difference must vs. may-type-change for these
>> cases. I'm not convinced that the must-type-change code is correct.
>>
>
> I did, even though it's not always easy because the patch is so old.
> However, the reasoning is as follows:
>
> 1) The callback will never report a known type if the "base address"
> of the RHS of the assignment is not exactly the same declaration or
> a MEM_REF of exactly the same SSA name.
>
> 2) The aliasing machinery is initialized to exactly the offset we are
> interested in and the size of one pointer:
>
> ao.offset = offset;
> ao.size = POINTER_SIZE;
>
> So, either the access which can alter the virtual table pointer is
> based on a different pointer and then we will not attempt to claim we
> know the type or the aliasing machinery invokes the callback only for
> the correct offset, because it can disambiguate between those based on
> the same thing. Does that make sense?
Not for the latter - the alias machinery reports may-aliases, thus
if you ask for [32, 36] then the alias machinery will invoke the
callback for a[i].vptr as well (the access with a variable offset
makes it [0, -1U], thus coverting [32, 46]). You have to check for
a must-alias relationship explicitely, which you cannot with the
information you have, once a possibly variable offset component
is visited. Note that the alias machinery may validly invoke your
callback for all stores, even those that trivially do not alias - saying
they may-alias is still correct.
> (One further reason why I did not think about arrays that much is that
> we will currently never attempt to search for BINFOs if there are
> arrays involved in any way, though I understand we may change that in
> the future. BTW, I spent quite some time attempting to break this
> code on Thursday but did not succeed even when I removed the check 1
> and the analysis produced clearly wrong results because of how we
> store the known type jump functions today and search for BINFOs only
> very much later on, checking the expected type is there at the
> expected offset in the type hierarchy of the type of the whole
> declaration. Of course, I understand the analysis has to be correct
> nevertheless and I tried to make it conservative.)
So I think you should explicitely not handle all variable-offset components
and pass down the actual offset of the pointer to the walker callback so
it can verify that the offsets match.
Richard.
> Thanks,
>
> Martin
>
>
>
>> Richard.
>>
>>
>> >
>> >> > + if (TREE_CODE (obj) == MEM_REF)
>> >> > + obj = TREE_OPERAND (obj, 0);
>> >> > + if (TREE_CODE (obj) == ADDR_EXPR)
>> >> > + obj = TREE_OPERAND (obj, 0);
>> >> > + if (obj != analyzed_obj)
>> >> > + return NULL_TREE;
>> >> > +
>> >> > + t = gimple_assign_rhs1 (stmt);
>> >> > + if (TREE_CODE (t) != ADDR_EXPR)
>> >> > + return NULL_TREE;
>> >> > + t = get_base_address (TREE_OPERAND (t, 0));
>> >>
>> >> Do we actually ever store sth else than the plain address of a
>> >> virtual table (thus, &decl)? If so, what difference makes the offset
>> >> into the virtual table we get in this way? I ask, because ...
>> >>
>> >> > + if (!t || TREE_CODE (t) != VAR_DECL || !DECL_VIRTUAL_P (t))
>> >> > + return NULL_TREE;
>> >> > +
>> >> > + return DECL_CONTEXT (t);
>> >>
>> >> ... DECL_CONTEXT (t) is of course independent of any offset.
>> >>
>> >> Thus I think you should drop the call to get_base_address () and
>> >> instead just look at TREE_OPERAND (t, 0).
>> >
>> > Even the simplest cases of assignments have basically a form like
>> > this:
>> >
>> > this_1(D)->_vptr.A = &MEM[(void *)&_ZTV1A + 8B];
>> >
>> > so I need to extract the actual VAR_DECL somehow. But of course I can
>> > do that by looking through the MEM_REF and ADDR_EXPR by hand, if
>> > preferable.
>> >
>> >>
>> >> > +}
>> >> > +
>> >> > /* Callback of walk_aliased_vdefs and a helper function for
>> >> > detect_type_change to check whether a particular statement may modify
>> >> > the virtual table pointer, and if possible also determine the new type of
>> >> > @@ -352,6 +404,12 @@ check_stmt_for_type_change (ao_ref *ao A
>> >> >
>> >> > if (stmt_may_be_vtbl_ptr_store (stmt))
>> >> > {
>> >> > + tree type;
>> >> > + type = extr_type_from_vtbl_ptr_store (stmt, tci->object);
>> >> > + if (tci->type_maybe_changed
>> >> > + && type != tci->known_current_type)
>> >> > + tci->multiple_types_encountered = true;
>> >> > + tci->known_current_type = type;
>> >> > tci->type_maybe_changed = true;
>> >> > return true;
>> >> > }
>> >> > @@ -359,19 +417,19 @@ check_stmt_for_type_change (ao_ref *ao A
>> >> > return false;
>> >> > }
>> >> >
>> >> > -/* Detect whether the dynamic type of ARG has changed (before callsite CALL) by
>> >> > - looking for assignments to its virtual table pointer. If it is, return true
>> >> > - and fill in the jump function JFUNC with relevant type information or set it
>> >> > - to unknown. ARG is the object itself (not a pointer to it, unless
>> >> > - dereferenced). BASE is the base of the memory access as returned by
>> >> > - get_ref_base_and_extent, as is the offset. */
>> >> > +
>> >> > +
>> >> > +/* Like detect_type_change but with extra argument COMP_TYPE which will become
>> >> > + the component type part of new JFUNC of dynamic type change is detected and
>> >> > + the new base type is identified. */
>> >> >
>> >> > static bool
>> >> > -detect_type_change (tree arg, tree base, gimple call,
>> >> > - struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
>> >> > +detect_type_change_1 (tree arg, tree base, tree comp_type, gimple call,
>> >> > + struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
>> >> > {
>> >> > struct type_change_info tci;
>> >> > ao_ref ao;
>> >> > + tree t;
>> >> >
>> >> > gcc_checking_assert (DECL_P (arg)
>> >> > || TREE_CODE (arg) == MEM_REF
>> >> > @@ -381,8 +439,6 @@ detect_type_change (tree arg, tree base,
>> >> > if (!flag_devirtualize || !gimple_vuse (call))
>> >> > return false;
>> >> >
>> >> > - tci.type_maybe_changed = false;
>> >> > -
>> >> > ao.ref = arg;
>> >> > ao.base = base;
>> >> > ao.offset = offset;
>> >> > @@ -391,15 +447,51 @@ detect_type_change (tree arg, tree base,
>> >> > ao.ref_alias_set = -1;
>> >> > ao.base_alias_set = -1;
>> >> >
>> >> > + t = arg;
>> >> > + while (handled_component_p (t))
>> >> > + t = TREE_OPERAND (t, 0);
>> >>
>> >> Here you are using handled_component_p, thus allow ARRAY_REFs ...
>> >> but you are not trying to distinguish a[1] from a[2] anywhere, so this
>> >> looks bogus and instead should look like the case above (with a comment
>> >> as to why looking at ARRAY_REFs would be bogus).
>> >
>> > I changed both to get_base_address as described above.
>> >
>> > This is the new version of the patch which I'm currently bootstrapping
>> > and testing on an x86_64-linux. OK for trunk if it passes? Thanks.
>> >
>> > Martin
>> >
>> >
>> > 2011-10-27 Martin Jambor <mjambor@suse.cz>
>> >
>> > * ipa-prop.c (type_change_info): New fields object, known_current_type
>> > and multiple_types_encountered.
>> > (extr_type_from_vtbl_ptr_store): New function.
>> > (check_stmt_for_type_change): Use it, set multiple_types_encountered if
>> > the result is different from the previous one.
>> > (detect_type_change): Renamed to detect_type_change_1. New parameter
>> > comp_type. Set up new fields in tci, build known type jump
>> > functions if the new type can be identified.
>> > (detect_type_change): New function.
>> > * tree.h (DECL_CONTEXT): Comment new use.
>> >
>> > * testsuite/g++.dg/ipa/devirt-c-1.C: Add dump scans.
>> > * testsuite/g++.dg/ipa/devirt-c-2.C: Likewise.
>> > * testsuite/g++.dg/ipa/devirt-c-7.C: New test.
>> >
>> >
>> > Index: src/gcc/ipa-prop.c
>> > ===================================================================
>> > --- src.orig/gcc/ipa-prop.c
>> > +++ src/gcc/ipa-prop.c
>> > @@ -271,8 +271,17 @@ ipa_print_all_jump_functions (FILE *f)
>> >
>> > struct type_change_info
>> > {
>> > + /* The declaration or SSA_NAME pointer of the base that we are checking for
>> > + type change. */
>> > + tree object;
>> > + /* If we actually can tell the type that the object has changed to, it is
>> > + stored in this field. Otherwise it remains NULL_TREE. */
>> > + tree known_current_type;
>> > /* Set to true if dynamic type change has been detected. */
>> > bool type_maybe_changed;
>> > + /* Set to true if multiple types have been encountered. known_current_type
>> > + must be disregarded in that case. */
>> > + bool multiple_types_encountered;
>> > };
>> >
>> > /* Return true if STMT can modify a virtual method table pointer.
>> > @@ -338,6 +347,44 @@ stmt_may_be_vtbl_ptr_store (gimple stmt)
>> > return true;
>> > }
>> >
>> > +/* If STMT can be proved to be an assignment to the virtual method table
>> > + pointer of ANALYZED_OBJ and the type associated with the new table
>> > + identified, return the type. Otherwise return NULL_TREE. */
>> > +
>> > +static tree
>> > +extr_type_from_vtbl_ptr_store (gimple stmt, tree analyzed_obj)
>> > +{
>> > + tree lhs, t, obj;
>> > +
>> > + if (!gimple_assign_single_p (stmt))
>> > + return NULL_TREE;
>> > +
>> > + lhs = gimple_assign_lhs (stmt);
>> > +
>> > + if (TREE_CODE (lhs) != COMPONENT_REF
>> > + || !DECL_VIRTUAL_P (TREE_OPERAND (lhs, 1)))
>> > + return NULL_TREE;
>> > +
>> > + obj = get_base_address (lhs);
>> > + if (TREE_CODE (obj) == MEM_REF)
>> > + {
>> > + if (TREE_CODE (analyzed_obj) != MEM_REF
>> > + || TREE_OPERAND (analyzed_obj, 0) != TREE_OPERAND (obj, 0))
>> > + return NULL_TREE;
>> > + }
>> > + else if (analyzed_obj != obj)
>> > + return NULL_TREE;
>> > +
>> > + t = gimple_assign_rhs1 (stmt);
>> > + if (TREE_CODE (t) != ADDR_EXPR)
>> > + return NULL_TREE;
>> > + t = get_base_address (TREE_OPERAND (t, 0));
>> > + if (!t || TREE_CODE (t) != VAR_DECL || !DECL_VIRTUAL_P (t))
>> > + return NULL_TREE;
>> > +
>> > + return DECL_CONTEXT (t);
>> > +}
>> > +
>> > /* Callback of walk_aliased_vdefs and a helper function for
>> > detect_type_change to check whether a particular statement may modify
>> > the virtual table pointer, and if possible also determine the new type of
>> > @@ -352,6 +399,12 @@ check_stmt_for_type_change (ao_ref *ao A
>> >
>> > if (stmt_may_be_vtbl_ptr_store (stmt))
>> > {
>> > + tree type;
>> > + type = extr_type_from_vtbl_ptr_store (stmt, tci->object);
>> > + if (tci->type_maybe_changed
>> > + && type != tci->known_current_type)
>> > + tci->multiple_types_encountered = true;
>> > + tci->known_current_type = type;
>> > tci->type_maybe_changed = true;
>> > return true;
>> > }
>> > @@ -359,16 +412,15 @@ check_stmt_for_type_change (ao_ref *ao A
>> > return false;
>> > }
>> >
>> > -/* Detect whether the dynamic type of ARG has changed (before callsite CALL) by
>> > - looking for assignments to its virtual table pointer. If it is, return true
>> > - and fill in the jump function JFUNC with relevant type information or set it
>> > - to unknown. ARG is the object itself (not a pointer to it, unless
>> > - dereferenced). BASE is the base of the memory access as returned by
>> > - get_ref_base_and_extent, as is the offset. */
>> > +
>> > +
>> > +/* Like detect_type_change but with extra argument COMP_TYPE which will become
>> > + the component type part of new JFUNC of dynamic type change is detected and
>> > + the new base type is identified. */
>> >
>> > static bool
>> > -detect_type_change (tree arg, tree base, gimple call,
>> > - struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
>> > +detect_type_change_1 (tree arg, tree base, tree comp_type, gimple call,
>> > + struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
>> > {
>> > struct type_change_info tci;
>> > ao_ref ao;
>> > @@ -381,8 +433,6 @@ detect_type_change (tree arg, tree base,
>> > if (!flag_devirtualize || !gimple_vuse (call))
>> > return false;
>> >
>> > - tci.type_maybe_changed = false;
>> > -
>> > ao.ref = arg;
>> > ao.base = base;
>> > ao.offset = offset;
>> > @@ -391,15 +441,44 @@ detect_type_change (tree arg, tree base,
>> > ao.ref_alias_set = -1;
>> > ao.base_alias_set = -1;
>> >
>> > + tci.object = get_base_address (arg);
>> > + tci.known_current_type = NULL_TREE;
>> > + tci.type_maybe_changed = false;
>> > + tci.multiple_types_encountered = false;
>> > +
>> > walk_aliased_vdefs (&ao, gimple_vuse (call), check_stmt_for_type_change,
>> > &tci, NULL);
>> > if (!tci.type_maybe_changed)
>> > return false;
>> >
>> > - jfunc->type = IPA_JF_UNKNOWN;
>> > + if (!tci.known_current_type
>> > + || tci.multiple_types_encountered
>> > + || offset != 0)
>> > + jfunc->type = IPA_JF_UNKNOWN;
>> > + else
>> > + {
>> > + jfunc->type = IPA_JF_KNOWN_TYPE;
>> > + jfunc->value.known_type.base_type = tci.known_current_type;
>> > + jfunc->value.known_type.component_type = comp_type;
>> > + }
>> > +
>> > return true;
>> > }
>> >
>> > +/* Detect whether the dynamic type of ARG has changed (before callsite CALL) by
>> > + looking for assignments to its virtual table pointer. If it is, return true
>> > + and fill in the jump function JFUNC with relevant type information or set it
>> > + to unknown. ARG is the object itself (not a pointer to it, unless
>> > + dereferenced). BASE is the base of the memory access as returned by
>> > + get_ref_base_and_extent, as is the offset. */
>> > +
>> > +static bool
>> > +detect_type_change (tree arg, tree base, gimple call,
>> > + struct ipa_jump_func *jfunc, HOST_WIDE_INT offset)
>> > +{
>> > + return detect_type_change_1 (arg, base, TREE_TYPE (arg), call, jfunc, offset);
>> > +}
>> > +
>> > /* Like detect_type_change but ARG is supposed to be a non-dereferenced pointer
>> > SSA name (its dereference will become the base and the offset is assumed to
>> > be zero). */
>> > @@ -407,16 +486,19 @@ detect_type_change (tree arg, tree base,
>> > static bool
>> > detect_type_change_ssa (tree arg, gimple call, struct ipa_jump_func *jfunc)
>> > {
>> > + tree comp_type;
>> > +
>> > gcc_checking_assert (TREE_CODE (arg) == SSA_NAME);
>> > if (!flag_devirtualize
>> > || !POINTER_TYPE_P (TREE_TYPE (arg))
>> > || TREE_CODE (TREE_TYPE (TREE_TYPE (arg))) != RECORD_TYPE)
>> > return false;
>> >
>> > + comp_type = TREE_TYPE (TREE_TYPE (arg));
>> > arg = build2 (MEM_REF, ptr_type_node, arg,
>> > - build_int_cst (ptr_type_node, 0));
>> > + build_int_cst (ptr_type_node, 0));
>> >
>> > - return detect_type_change (arg, arg, call, jfunc, 0);
>> > + return detect_type_change_1 (arg, arg, comp_type, call, jfunc, 0);
>> > }
>> >
>> > /* Callback of walk_aliased_vdefs. Flags that it has been invoked to the
>> > Index: src/gcc/testsuite/g++.dg/ipa/devirt-c-1.C
>> > ===================================================================
>> > --- src.orig/gcc/testsuite/g++.dg/ipa/devirt-c-1.C
>> > +++ src/gcc/testsuite/g++.dg/ipa/devirt-c-1.C
>> > @@ -1,7 +1,7 @@
>> > /* Verify that ipa-cp correctly detects the dynamic type of an object
>> > under construction when doing devirtualization. */
>> > /* { dg-do run } */
>> > -/* { dg-options "-O3 -fno-early-inlining -fno-inline" } */
>> > +/* { dg-options "-O3 -fno-early-inlining -fno-inline -fdump-ipa-cp -fdump-tree-optimized" } */
>> >
>> > extern "C" void abort (void);
>> >
>> > @@ -69,3 +69,8 @@ int main (int argc, char *argv[])
>> > bah ();
>> > return 0;
>> > }
>> > +
>> > +/* { dg-final { scan-ipa-dump "Discovered a virtual call to a known target.*A::foo" "cp" } } */
>> > +/* { dg-final { scan-tree-dump-times "OBJ_TYPE_REF" 0 "optimized"} } */
>> > +/* { dg-final { cleanup-ipa-dump "cp" } } */
>> > +/* { dg-final { cleanup-tree-dump "optimized" } } */
>> > Index: src/gcc/testsuite/g++.dg/ipa/devirt-c-2.C
>> > ===================================================================
>> > --- src.orig/gcc/testsuite/g++.dg/ipa/devirt-c-2.C
>> > +++ src/gcc/testsuite/g++.dg/ipa/devirt-c-2.C
>> > @@ -1,7 +1,7 @@
>> > /* Verify that ipa-cp correctly detects the dynamic type of an object
>> > under construction when doing devirtualization. */
>> > /* { dg-do run } */
>> > -/* { dg-options "-O3 -fno-early-inlining -fno-inline" } */
>> > +/* { dg-options "-O3 -fno-early-inlining -fno-inline -fdump-ipa-cp -fdump-tree-optimized" } */
>> >
>> > extern "C" void abort (void);
>> >
>> > @@ -77,3 +77,8 @@ int main (int argc, char *argv[])
>> > bah ();
>> > return 0;
>> > }
>> > +
>> > +/* { dg-final { scan-ipa-dump "Discovered a virtual call to a known target.*A::foo" "cp" } } */
>> > +/* { dg-final { scan-tree-dump-times "OBJ_TYPE_REF" 0 "optimized"} } */
>> > +/* { dg-final { cleanup-ipa-dump "cp" } } */
>> > +/* { dg-final { cleanup-tree-dump "optimized" } } */
>> > Index: src/gcc/tree.h
>> > ===================================================================
>> > --- src.orig/gcc/tree.h
>> > +++ src/gcc/tree.h
>> > @@ -2678,7 +2678,9 @@ struct function;
>> > nodes, this points to either the FUNCTION_DECL for the containing
>> > function, the RECORD_TYPE or UNION_TYPE for the containing type, or
>> > NULL_TREE or a TRANSLATION_UNIT_DECL if the given decl has "file
>> > - scope". */
>> > + scope". In particular, for VAR_DECLs which are virtual table pointers
>> > + (they have DECL_VIRTUAL set), we use DECL_CONTEXT to determine the type
>> > + they belong to. */
>> > #define DECL_CONTEXT(NODE) (DECL_MINIMAL_CHECK (NODE)->decl_minimal.context)
>> > #define DECL_FIELD_CONTEXT(NODE) \
>> > (FIELD_DECL_CHECK (NODE)->decl_minimal.context)
>> > Index: src/gcc/testsuite/g++.dg/ipa/devirt-c-7.C
>> > ===================================================================
>> > --- /dev/null
>> > +++ src/gcc/testsuite/g++.dg/ipa/devirt-c-7.C
>> > @@ -0,0 +1,87 @@
>> > +/* Verify that ipa-cp will not get confused by placement new constructing an
>> > + object within another one when looking for dynamic type change . */
>> > +/* { dg-do run } */
>> > +/* { dg-options "-O3 -Wno-attributes" } */
>> > +
>> > +extern "C" void abort (void);
>> > +namespace std {
>> > + typedef __SIZE_TYPE__ size_t;
>> > +}
>> > +inline void* __attribute__ ((always_inline))
>> > +operator new(std::size_t, void* __p) throw()
>> > +{
>> > + return __p;
>> > +}
>> > +
>> > +class A
>> > +{
>> > +public:
>> > + char data[256];
>> > + A();
>> > + virtual int foo (int i);
>> > +};
>> > +
>> > +class B : public A
>> > +{
>> > +public:
>> > + virtual int foo (int i);
>> > +};
>> > +
>> > +class C
>> > +{
>> > +public:
>> > + C();
>> > + virtual double foo (double i);
>> > +};
>> > +
>> > +int A::foo (int i)
>> > +{
>> > + return i + 1;
>> > +}
>> > +
>> > +int B::foo (int i)
>> > +{
>> > + return i + 2;
>> > +}
>> > +
>> > +double C::foo (double i)
>> > +{
>> > + return i + 3.5;
>> > +}
>> > +
>> > +static int __attribute__ ((noinline)) middleman (class A *obj, int i)
>> > +{
>> > + return obj->foo (i);
>> > +}
>> > +
>> > +int __attribute__ ((noinline,noclone)) get_input(void)
>> > +{
>> > + return 1;
>> > +}
>> > +
>> > +__attribute__ ((always_inline)) C::C ()
>> > +{
>
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