[Bug c++/41874] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[jason at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

Jason Merrill  changed:

   What|Removed |Added

  Known to fail||6.5.0
 CC||jason at gcc dot gnu.org
  Known to work||7.5.0
   Target Milestone|--- |7.0
 Status|REOPENED|RESOLVED
 Resolution|--- |FIXED

--- Comment #17 from Jason Merrill  ---
(In reply to Aso Renji from comment #15)
> No, this warning still appear if (and only if) you use -O2 or -O3
> optimization key (as it be in startpost with "g++ -O3 -Wstrict-aliasing
> test.cc -o /dev/null" line).

I don't see this with any compiler after 6.5.0.

[Bug c++/41874] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

Andrew Pinski  changed:

   What|Removed |Added

   Target Milestone|4.5.0   |---

[Bug c++/94951] [8/9 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Andrew Pinski  changed:

   What|Removed |Added

 CC||a-yee at u dot northwestern.edu

--- Comment #12 from Andrew Pinski  ---
*** Bug 91343 has been marked as a duplicate of this bug. ***

[Bug c++/94951] [8/9 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Andrew Pinski  changed:

   What|Removed |Added

 CC||rrrlasse at hotmail dot com

--- Comment #11 from Andrew Pinski  ---
*** Bug 81152 has been marked as a duplicate of this bug. ***

[Bug c++/94951] [8/9 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Jakub Jelinek  changed:

   What|Removed |Added

 Resolution|--- |FIXED
 Status|ASSIGNED|RESOLVED

--- Comment #10 from Jakub Jelinek  ---
Fixed for 8.5 in r8-10503-g79a11b9833baa91cef7c881532e01470fa25047f and by the
above commit for 9.4+ too.

[Bug c++/94951] [8/9 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

--- Comment #9 from CVS Commits  ---
The releases/gcc-9 branch has been updated by Jakub Jelinek
:

https://gcc.gnu.org/g:eca1dbea010ba4c18ccec90bacbad5d8ec72c09f

commit r9-8897-geca1dbea010ba4c18ccec90bacbad5d8ec72c09f
Author: Jakub Jelinek 
Date:   Wed May 6 23:38:13 2020 +0200

c++: Avoid strict_aliasing_warning on dependent types or expressions
[PR94951]

The following testcase gets a bogus warning during build_base_path,
when cp_build_indirect_ref* calls strict_aliasing_warning with a dependent
expression.  IMHO calling get_alias_set etc. on dependent types feels wrong
to me, we should just defer the warnings in those cases until instantiation
and only handle the cases where neither type nor expr are dependent.

2020-05-06  Jakub Jelinek  

PR c++/94951
* typeck.c (cp_strict_aliasing_warning): New function.
(cp_build_indirect_ref_1, build_reinterpret_cast_1): Use
it instead of strict_aliasing_warning.

* g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C: New test.

(cherry picked from commit d82414ebcf7716ea24688510594a2c464a105908)

[Bug c++/94951] [8/9 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Jakub Jelinek  changed:

   What|Removed |Added

Summary|[8/9/10/11 Regression]  |[8/9 Regression]
   |dereferencing type-punned   |dereferencing type-punned
   |pointer will break  |pointer will break
   |strict-aliasing rules when  |strict-aliasing rules when
   |using super class for a |using super class for a
   |template type   |template type

--- Comment #8 from Jakub Jelinek  ---
Fixed for 10.2+ and 11+ so far.

[Bug c++/94951] [8/9/10/11 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

--- Comment #7 from CVS Commits  ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
:

https://gcc.gnu.org/g:d82414ebcf7716ea24688510594a2c464a105908

commit r10-8115-gd82414ebcf7716ea24688510594a2c464a105908
Author: Jakub Jelinek 
Date:   Wed May 6 23:38:13 2020 +0200

c++: Avoid strict_aliasing_warning on dependent types or expressions
[PR94951]

The following testcase gets a bogus warning during build_base_path,
when cp_build_indirect_ref* calls strict_aliasing_warning with a dependent
expression.  IMHO calling get_alias_set etc. on dependent types feels wrong
to me, we should just defer the warnings in those cases until instantiation
and only handle the cases where neither type nor expr are dependent.

2020-05-06  Jakub Jelinek  

PR c++/94951
* typeck.c (cp_strict_aliasing_warning): New function.
(cp_build_indirect_ref_1, build_reinterpret_cast_1): Use
it instead of strict_aliasing_warning.

* g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C: New test.

[Bug c++/94951] [8/9/10/11 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

--- Comment #6 from CVS Commits  ---
The master branch has been updated by Jakub Jelinek :

https://gcc.gnu.org/g:46fcef99f49cc2d9f28d98f8ecdbf8263e9e0a87

commit r11-153-g46fcef99f49cc2d9f28d98f8ecdbf8263e9e0a87
Author: Jakub Jelinek 
Date:   Wed May 6 23:38:13 2020 +0200

c++: Avoid strict_aliasing_warning on dependent types or expressions
[PR94951]

The following testcase gets a bogus warning during build_base_path,
when cp_build_indirect_ref* calls strict_aliasing_warning with a dependent
expression.  IMHO calling get_alias_set etc. on dependent types feels wrong
to me, we should just defer the warnings in those cases until instantiation
and only handle the cases where neither type nor expr are dependent.

2020-05-06  Jakub Jelinek  

PR c++/94951
* typeck.c (cp_strict_aliasing_warning): New function.
(cp_build_indirect_ref_1, build_reinterpret_cast_1): Use
it instead of strict_aliasing_warning.

* g++.dg/warn/Wstrict-aliasing-bogus-tmpl.C: New test.

[Bug c++/94951] [8/9/10/11 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Jakub Jelinek  changed:

   What|Removed |Added

 Status|NEW |ASSIGNED
   Assignee|unassigned at gcc dot gnu.org  |jakub at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek  ---
Created attachment 48456
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48456=edit
gcc11-pr94951.patch

Untested fix.  It seems just wrong to call the c-family strict_aliasing_warning
for dependent types, we shouldn't query alias sets of dependent types and do
any decisions based on what that gives.

[Bug c++/94951] [8/9/10/11 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Jakub Jelinek  changed:

   What|Removed |Added

   Priority|P3  |P2

[Bug c++/94951] [8/9/10/11 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

--- Comment #4 from Jakub Jelinek  ---
And the array isn't needed either:
struct A { int a; };
template 
struct B : public A
{
  static B foo () { B t; t.a = 4; return t; }
};

[Bug c++/94951] [8/9/10/11 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

--- Comment #3 from Jakub Jelinek  ---
Slightly simplified testcase:
struct A { unsigned a[32]; };
template 
struct B : public A
{
  static B foo () { B t; t.a[0] = 4; return t; }
};

[Bug c++/94951] [8/9/10/11 Regression] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Jakub Jelinek  changed:

   What|Removed |Added

   Target Milestone|--- |8.5
 CC||jakub at gcc dot gnu.org,
   ||jason at gcc dot gnu.org
Summary|dereferencing type-punned   |[8/9/10/11 Regression]
   |pointer will break  |dereferencing type-punned
   |strict-aliasing rules when  |pointer will break
   |using super class for a |strict-aliasing rules when
   |template type   |using super class for a
   ||template type

--- Comment #2 from Jakub Jelinek  ---
Started with r7-755-g23cb72663051cd3f5a8952d4aa2186d50243b7d0

[Bug c++/94951] dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Richard Biener  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
 Ever confirmed|0   |1
   Keywords||diagnostic
   Last reconfirmed||2020-05-05

--- Comment #1 from Richard Biener  ---
We're warning via

#0  warning_at (location=426247, opt=664, 
gmsgid=0x2a36f08 "dereferencing type-punned pointer will break
strict-aliasing rules") at ../../src/trunk/gcc/diagnostic.c:1442
#1  0x00e324c9 in strict_aliasing_warning (loc=426247, 
type=, expr=)
at ../../src/trunk/gcc/c-family/c-warn.c:729
#2  0x00d45def in cp_build_indirect_ref_1 (loc=426535, 
ptr=, errorstring=RO_NULL, complain=3, 
do_fold=true) at ../../src/trunk/gcc/cp/typeck.c:3364
#3  0x00d46191 in cp_build_fold_indirect_ref (
pointer=) at ../../src/trunk/gcc/cp/typeck.c:3444
#4  0x009ecb7a in build_base_path (code=PLUS_EXPR, 
expr=, binfo=, 
nonnull=1, complain=3) at ../../src/trunk/gcc/cp/class.c:513
#5  0x00d4309f in build_class_member_access_expr (object=..., 
member=, 
access_path=, preserve_reference=false, 
complain=3) at ../../src/trunk/gcc/cp/typeck.c:2603
#6  0x00d45377 in finish_class_member_access_expr (object=..., 
name=, template_p=false, 
complain=3) at ../../src/trunk/gcc/cp/typeck.c:3209

[Bug c++/94951] New: dereferencing type-punned pointer will break strict-aliasing rules when using super class for a template type

[jorgen.lind at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94951

Bug ID: 94951
   Summary: dereferencing type-punned pointer will break
strict-aliasing rules when using super class for a
template type
   Product: gcc
   Version: 9.3.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: jorgen.lind at gmail dot com
  Target Milestone: ---

The following program issues the warning when compiled with -O2 or -O3.

The workaround is to static_cast usage of members to super class.
In the godbolt example its sufficient to add brackets around the class instance
before member access, but was not sufficient in a more complex example. 

The behavior is present from 7.1 until trunk.
Godbolt link:https://godbolt.org/z/Kfp-ac

#include 

struct A
{
uint32_t someData[32];
};

template
struct B : public A
{
static B createB(uint32_t ()[32])
{
B toReturn;
toReturn.someData[2] = 4;
return toReturn;
}
};

[Bug c/94337] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94337

--- Comment #2 from Vincent Lefèvre  ---
Why not having a level with no false positives? This would avoid to disable the
warning globally.

IMHO, using it when a union is involved is likely to generate false positives.

[Bug c/94337] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94337

--- Comment #1 from Richard Biener  ---
The warning only looks at the single expression it quotes which isn't really
enough to discover you are doing right.  It tries to be helpful - if you know
better then disable the warning.

[Bug c/94337] New: Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94337

Bug ID: 94337
   Summary: Incorrect "dereferencing type-punned pointer will
    break strict-aliasing rules" warning
   Product: gcc
   Version: 10.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
  Assignee: unassigned at gcc dot gnu.org
  Reporter: vincent-gcc at vinc17 dot net
  Target Milestone: ---

Consider the following example.

#include 

struct s1
{
  int a;
};

struct s2
{
  int a, b;
};

int main (void)
{
  union {
struct s1 m1[1];
struct s2 m2[1];
  } u;

  (u.m2)->b = 17;
  printf ("%d\n", ((struct s2 *) (struct s1 *) u.m2)->b);
  printf ("%d\n", ((struct s2 *) u.m1)->b);
  return 0;
}

zira:~> gcc-10 tst.c -o tst -O2 -Wstrict-aliasing
tst.c: In function ‘main’:
tst.c:22:20: warning: dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]
   22 |   printf ("%d\n", ((struct s2 *) u.m1)->b);
  |   ~^~~

But there is no type-punning here. All accesses are done via struct s2.
Everything else is pointer conversions, which are not related to the aliasing
rules.

[Bug c++/41874] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

Jonathan Wakely  changed:

   What|Removed |Added

 Status|RESOLVED|REOPENED
 Resolution|FIXED   |---

--- Comment #16 from Jonathan Wakely  ---
(In reply to Richard Biener from comment #12)
> No, the warning is gone from all releases that are still maintained.

Looks like this wasn't true.

[Bug c++/41874] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[asorenji at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

--- Comment #15 from Aso Renji  ---
(In reply to Jonathan Wakely from comment #14)
> What do you mean by "same problem"? The original testcase does not produce a 
> warning with GCC 6.3.0
No, this warning still appear if (and only if) you use -O2 or -O3 optimization
key (as it be in startpost with "g++ -O3 -Wstrict-aliasing test.cc -o
/dev/null" line).

If I don't use any optimization - yes, this warning don't appeared.

[Bug c++/41874] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

--- Comment #14 from Jonathan Wakely  ---
(In reply to Aso Renji from comment #13)
> Still have same problem in g++ 6.3.0. So, please reopen this bug.

What do you mean by "same problem"? The original testcase does not produce a
warning with GCC 6.3.0

If you get a warning for a different piece of code then please open a new bug,
this one is fixed.

[Bug c++/41874] Incorrect "dereferencing type-punned pointer will break strict-aliasing rules" warning

[asorenji at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

Aso Renji  changed:

   What|Removed |Added

 CC||asorenji at gmail dot com

--- Comment #13 from Aso Renji  ---
Still have same problem in g++ 6.3.0. So, please reopen this bug.

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Jonathan Wakely  changed:

   What|Removed |Added

 CC||joerg.rich...@pdv-fs.de

--- Comment #15 from Jonathan Wakely  ---
*** Bug 81858 has been marked as a duplicate of this bug. ***

[Bug c++/81145] bogus "dereferencing type-punned pointer will break strict-aliasing rules" diagnostic with incomplete class type

[richard-gccbugzilla at metafoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81145

--- Comment #5 from Richard Smith  ---
Yes, according to godbolt this occurs in GCC 4.4 - 7.1, but not in trunk.
Unlike PR80593, it does not appear to be a GCC 7 regression, but it sure seems
plausible that that change fixed it =)

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Jonathan Wakely  changed:

   What|Removed |Added

 CC||richard-gccbugzilla@metafoo
   ||.co.uk

--- Comment #14 from Jonathan Wakely  ---
*** Bug 81145 has been marked as a duplicate of this bug. ***

[Bug c++/81145] bogus "dereferencing type-punned pointer will break strict-aliasing rules" diagnostic with incomplete class type

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81145

Jonathan Wakely  changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |DUPLICATE

--- Comment #4 from Jonathan Wakely  ---
Indeed, the warning is gone with a current gcc-7-branch build.

*** This bug has been marked as a duplicate of bug 80593 ***

[Bug c++/81145] bogus "dereferencing type-punned pointer will break strict-aliasing rules" diagnostic with incomplete class type

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81145

--- Comment #3 from Jonathan Wakely  ---
Is the version 7.0.1 correct? Unless you're still seeing this with a fairly
recent 7.1.1 build from the gcc-7-branch this is probably a dup of Bug 80593

[Bug c++/81145] bogus "dereferencing type-punned pointer will break strict-aliasing rules" diagnostic with incomplete class type

[richard-gccbugzilla at metafoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81145

--- Comment #2 from Richard Smith  ---
I've tried a few things and not found any way to get wrong code. I think you're
right that this is just a diagnostic issue.

[Bug c++/81145] bogus "dereferencing type-punned pointer will break strict-aliasing rules" diagnostic with incomplete class type

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81145

Marc Glisse  changed:

   What|Removed |Added

   Keywords||diagnostic

--- Comment #1 from Marc Glisse  ---
Can you make it generate wrong code? I expect it is only the warning that is
broken.

[Bug c++/81145] New: bogus "dereferencing type-punned pointer will break strict-aliasing rules" diagnostic with incomplete class type

[richard-gccbugzilla at metafoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81145

Bug ID: 81145
   Summary: bogus "dereferencing type-punned pointer will break
    strict-aliasing rules" diagnostic with incomplete
class type
   Product: gcc
   Version: 7.0.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: richard-gccbugzilla at metafoo dot co.uk
  Target Milestone: ---

Testcase:

struct B { int n; };
struct A
#ifndef BUG
 { B b; }
#endif
;

extern A a;
int n = reinterpret_cast<B*>()->n;

This produces a bogus "dereferencing type-punned pointer will break
strict-aliasing rules" diagnostic with -DBUG, but correctly suppresses the
warning when the definition of A is visible.

Note that under C++ P0137R1 / DR1776, the A object is pointer-interconvertible
with its b member, so the reinterpret_cast produces a usable pointer to a.b,
regardless of whether the definition of A is visible.

Perhaps GCC's TBAA should be less aggressive when comparing an incomplete type
against (at least) a standard-layout type?

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[daniel.black at au dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

--- Comment #13 from Daniel Black  ---
Thanks Richard.

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Richard Biener  changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
  Known to work||7.1.1
 Resolution|--- |FIXED
  Known to fail||7.1.0

--- Comment #12 from Richard Biener  ---
Fixed.

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

--- Comment #11 from Richard Biener  ---
Author: rguenth
Date: Wed Jun  7 13:07:06 2017
New Revision: 248970

URL: https://gcc.gnu.org/viewcvs?rev=248970=gcc=rev
Log:
2017-06-07  Richard Biener  

Backport from mainline
2017-05-02  Richard Biener  

PR tree-optimization/80549
* tree-cfgcleanup.c (mfb_keep_latches): New helper.
(cleanup_tree_cfg_noloop): Create forwarders to known loop
headers if they do not have a preheader.

* gcc.dg/torture/pr80549.c: New testcase.

2017-05-19  Richard Biener  

PR c++/80593
* c-warn.c (strict_aliasing_warning): Do not warn for accesses
to alias-set zero memory.

* g++.dg/warn/Wstrict-aliasing-bogus-char-2.C: New testcase.
* g++.dg/warn/Wstrict-aliasing-6.C: Adjust expected outcome.

2017-05-26  Richard Biener  

PR tree-optimization/80842
* tree-ssa-ccp.c (set_lattice_value): Always meet with the old
value.

* gcc.dg/torture/pr80842.c: New testcase.

2017-05-31  Richard Biener  

PR tree-optimization/80906
* graphite-isl-ast-to-gimple.c (copy_loop_close_phi_nodes): Get
and pass through iv_map.
(copy_bb_and_scalar_dependences): Adjust.
(translate_pending_phi_nodes): Likewise.
(copy_loop_close_phi_args): Handle code-generating IVs instead
of ICEing.

* gcc.dg/graphite/pr80906.c: New testcase.

2017-05-11  Richard Biener  

PR tree-optimization/80705
* tree-vect-data-refs.c (vect_analyze_data_refs): DECL_NONALIASED
bases are not vectorizable.

* gcc.dg/vect/bb-slp-pr80705.c: New testcase.

Added:
   
branches/gcc-7-branch/gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-char-2.C
branches/gcc-7-branch/gcc/testsuite/gcc.dg/graphite/pr80906.c
branches/gcc-7-branch/gcc/testsuite/gcc.dg/torture/pr80549.c
branches/gcc-7-branch/gcc/testsuite/gcc.dg/torture/pr80842.c
branches/gcc-7-branch/gcc/testsuite/gcc.dg/vect/bb-slp-pr80705.c
Modified:
branches/gcc-7-branch/gcc/ChangeLog
branches/gcc-7-branch/gcc/c-family/ChangeLog
branches/gcc-7-branch/gcc/c-family/c-warn.c
branches/gcc-7-branch/gcc/graphite-isl-ast-to-gimple.c
branches/gcc-7-branch/gcc/testsuite/ChangeLog
branches/gcc-7-branch/gcc/testsuite/g++.dg/warn/Wstrict-aliasing-6.C
branches/gcc-7-branch/gcc/tree-cfgcleanup.c
branches/gcc-7-branch/gcc/tree-ssa-ccp.c
branches/gcc-7-branch/gcc/tree-vect-data-refs.c

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[daniel.black at au dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Daniel Black  changed:

   What|Removed |Added

 CC||daniel.black at au dot ibm.com

--- Comment #10 from Daniel Black  ---
FYI I have tested from the gcc master (x86_64-pc-linux-gnu-g++ (GCC) 8.0.0
20170605 (experimental)) and it doesn't identify the the following bit of
rocksdb code as a warning where previously it did. So fixed for me on master.

./db/write_thread.h:227:78: error: dereferencing type-punned pointer will break
strict-aliasing rules [-Werror=strict-aliasing]
   return
*static_cast<std::mutex*>(static_cast<void*>(_mutex_bytes));

ref: https://github.com/facebook/rocksdb/issues/2382

Still fails using the gcc at the head of the gcc-7-branch however

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[lists at coryfields dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Cory Fields  changed:

   What|Removed |Added

 CC||lists at coryfields dot com

--- Comment #9 from Cory Fields  ---
I assume based on the milestone that this will be backported to 7.2?

Boost's aligned_storage is affected as well, causing floods of warnings from
several of its containers (multi_index, at least) which use it.

[Bug c++/80593] [7 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Richard Biener  changed:

   What|Removed |Added

  Known to work||8.0
Summary|[7/8 Regression] GCC 7, |[7 Regression] GCC 7,
   |aligned_storage and |aligned_storage and
   |“dereferencing type-punned  |“dereferencing type-punned
   |pointer will break  |pointer will break
   |strict-aliasing rules”  |strict-aliasing rules”

--- Comment #8 from Richard Biener  ---
Fixed on trunk sofar.

[Bug c++/80593] [7/8 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

--- Comment #7 from Richard Biener  ---
Author: rguenth
Date: Fri May 19 12:34:54 2017
New Revision: 248269

URL: https://gcc.gnu.org/viewcvs?rev=248269=gcc=rev
Log:
2017-05-19  Richard Biener  

PR c++/80593
* c-warn.c (strict_aliasing_warning): Do not warn for accesses
to alias-set zero memory.

* g++.dg/warn/Wstrict-aliasing-bogus-char-2.C: New testcase.
* g++.dg/warn/Wstrict-aliasing-6.C: Adjust expected outcome.

Added:
trunk/gcc/testsuite/g++.dg/warn/Wstrict-aliasing-bogus-char-2.C
Modified:
trunk/gcc/c-family/ChangeLog
trunk/gcc/c-family/c-warn.c
trunk/gcc/testsuite/ChangeLog
trunk/gcc/testsuite/g++.dg/warn/Wstrict-aliasing-6.C

[Bug c++/80593] [7/8 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Richard Biener  changed:

   What|Removed |Added

 CC||s-beyer at gmx dot net

--- Comment #6 from Richard Biener  ---
*** Bug 80827 has been marked as a duplicate of this bug. ***

[Bug c++/80593] [7/8 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

--- Comment #5 from Richard Biener  ---
Breaks at least g++.dg/warn/Wstrict-aliasing-6.C which I think is expected
fallout.

[Bug c++/80593] [7/8 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Richard Biener  changed:

   What|Removed |Added

   Priority|P3  |P2
 Status|NEW |ASSIGNED
 CC||rguenth at gcc dot gnu.org
   Assignee|unassigned at gcc dot gnu.org  |rguenth at gcc dot 
gnu.org

--- Comment #4 from Richard Biener  ---
(In reply to Jakub Jelinek from comment #3)
> The set1 == 0 stuff has been added in r136679.

Yep, to not regress some -Wstrict-aliasing testcase I think.  I'll test

Index: gcc/c-family/c-warn.c
===
--- gcc/c-family/c-warn.c   (revision 248179)
+++ gcc/c-family/c-warn.c   (working copy)
@@ -537,10 +537,10 @@ strict_aliasing_warning (tree otype, tre
= get_alias_set (TREE_TYPE (TREE_OPERAND (expr, 0)));
  alias_set_type set2 = get_alias_set (TREE_TYPE (type));

- if (set1 != set2 && set2 != 0
- && (set1 == 0
- || (!alias_set_subset_of (set2, set1)
- && !alias_sets_conflict_p (set1, set2
+ if (set2 != 0
+ && set1 != set2
+ && !alias_set_subset_of (set2, set1)
+ && !alias_sets_conflict_p (set1, set2))
    {
  warning (OPT_Wstrict_aliasing, "dereferencing type-punned "
   "pointer will break strict-aliasing rules");

[Bug c++/80593] [7/8 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

--- Comment #3 from Jakub Jelinek  ---
The set1 == 0 stuff has been added in r136679.

[Bug c++/80593] [7/8 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Jakub Jelinek  changed:

   What|Removed |Added

 CC||jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek  ---
Indeed, started with r246866.

[Bug c++/80593] [7/8 Regression] GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Richard Biener  changed:

   What|Removed |Added

   Keywords||diagnostic
 Status|UNCONFIRMED |NEW
   Last reconfirmed||2017-05-02
   Target Milestone|--- |7.2
Summary|GCC 7, aligned_storage and  |[7/8 Regression] GCC 7,
   |“dereferencing type-punned  |aligned_storage and
   |pointer will break  |“dereferencing type-punned
   |strict-aliasing rules”  |pointer will break
   ||strict-aliasing rules”
 Ever confirmed|0   |1

--- Comment #1 from Richard Biener  ---
Confirmed.  This likely regressed with the introduction of
TYPE_TYPELESS_STORAGE which aligned_storage now is, and thus 'storage' gets
alias-set zero itself running into

  /* warn_strict_aliasing >= 3.   This includes the default (3).
 Only warn if the cast is dereferenced immediately.  */
  alias_set_type set1
= get_alias_set (TREE_TYPE (TREE_OPERAND (expr, 0)));
  alias_set_type set2 = get_alias_set (TREE_TYPE (type));

  if (set1 != set2 && set2 != 0
  && (set1 == 0
  || (!alias_set_subset_of (set2, set1)
  && !alias_sets_conflict_p (set1, set2
{
  warning (OPT_Wstrict_aliasing, "dereferencing type-punned "
       "pointer will break strict-aliasing rules");
  return true;

with set1 == 0.

[Bug c++/80593] New: GCC 7, aligned_storage and “dereferencing type-punned pointer will break strict-aliasing rules”

[freddie_chopin at op dot pl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80593

Bug ID: 80593
   Summary: GCC 7, aligned_storage and “dereferencing type-punned
pointer will break strict-aliasing rules”
   Product: gcc
   Version: 7.0.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: freddie_chopin at op dot pl
  Target Milestone: ---

I've posted this info to the gcc mailing list. Richard Biener suggested opening
a bug report, so here it is.

https://gcc.gnu.org/ml/gcc/2017-05/msg00013.html

Following example code is warning-free on GCC 4.9, GCC 5 and GCC 6. It is also
warning free on some older GCC 7 snapshots (like 7-20170409).

-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --

$ cat punning.cpp 
template
struct aligned_storage
{
  union type
{
  unsigned char __data[_Len];
  struct __attribute__((__aligned__((_Align { } __align;
};
};

aligned_storage<sizeof(int), alignof(int)>::type storage;

int main()
{
  *reinterpret_cast<int*>() = 42;
}
$ g++ -Wall -O2 -c punning.cpp 
$

-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --

However in the most recent GCC 7 snapshots (including both RCs), it gives a
warning about type punning:

-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --

$ g++ -Wall -O2 -c punning.cpp 
punning.cpp: In function 'int main()':
punning.cpp:15:35: warning: dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]
   *reinterpret_cast<int*>() = 42;
   ^
$

-- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 -- >8 --

dereferencing type-punned pointer will break strict-aliasing rules

[Marcel Behlau]

Hi,

i wan't to create aliase (name and type) for the elements of an 
char-array. Unfortunately my gcc produce the warning "dereferencing 
type-punned pointer will break strict-aliasing rules", if i use -O2 or 
bigger. Since i set -Werror, the warning will become an error.


I attached an example to this mail. To compile and generate the problem, 
i use "gcc -O2 -Werror -Wall main.cpp".


I found an workaround (without using pragma, or somethink else), with 
it's included in the code, too. To activate, pass an extra "-DWorking" 
to the gcc-Command. The workaround is working, but using an pointer is 
ugly.


Best regrads,

Marcel

--
Dipl. Ing (FH) Marcel Behlau
(Software Developer)

ELFIN GmbH
Siegburger Straße 215
50679 Köln
Germany

Tel: +49 (221) 6778932-0
Fax: +49 (221) 6778932-2
marcel.beh...@elfin.de
www.elfin.de

//gcc -O2 -Wall main.cpp
//gcc -O2 -Wall main.cpp -DWorking

//#define Working

struct Ec
{
  char ecData;
};

class ClassZero
{
public:
  char data[8];
  char* pointer;
  Ec& ec0;

#ifdef Working
  ClassZero() : pointer(data), ec0(*(Ec*)(pointer)) { }
#else
  ClassZero() : ec0(*(Ec*)(data)) { }
#endif

};

int main()
{
return 0;
} 

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874



Paolo Carlini paolo.carlini at oracle dot com changed:



   What|Removed |Added



 CC|gcc-bugs at gcc dot gnu.org |



--- Comment #11 from Paolo Carlini paolo.carlini at oracle dot com 2012-10-15 
09:27:13 UTC ---

Richard, is this still an issue?

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874



Richard Biener rguenth at gcc dot gnu.org changed:



   What|Removed |Added



 Status|NEW |RESOLVED

 Resolution||FIXED

   Target Milestone|--- |4.5.0



--- Comment #12 from Richard Biener rguenth at gcc dot gnu.org 2012-10-15 
09:45:11 UTC ---

No, the warning is gone from all releases that are still maintained.

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[muravev at yandex dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

--- Comment #9 from Ilya Murav'jov muravev at yandex dot ru 2010-10-06 
19:43:30 UTC ---
I've come across another weird warning emission in g++ 4.4:

$ cat test.cc
#include new
struct interface_type {

virtual interface_type* clone(void* storage) const
{
return ::new (storage) interface_type();
}
};

struct poly_base {

poly_base(const interface_type x) { x.clone(data); }

typedef char storage_t[100];
storage_t data;
};

struct instance_t: interface_type {};

int main()
{
instance_t pi;
poly_base p1(pi);

interface_type* ptr = (interface_type*)(p1.data);
poly_base p2(*ptr);
}
$ g++ -O3 -Wstrict-aliasing test.cc -o /dev/null
test.cc: In function ‘int main()’:
test.cc:12: warning: dereferencing pointer ‘ptr’ does break strict-aliasing
rules
test.cc:25: note: initialized from here

$ g++ -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu9'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9)

I get this only in g++ 4.4, g++ 4.5 does not warn.

I want to note that this is a different type of warning about strict-aliasing
rules, likely a more serious one. Can anyone tell what a difference between
warning: dereferencing type-punned pointer will break strict-aliasing rules
and warning: dereferencing pointer ‘ptr’ does break strict-aliasing rules?

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[rguenther at suse dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

--- Comment #10 from rguenther at suse dot de rguenther at suse dot de 
2010-10-06 20:56:56 UTC ---
On Wed, 6 Oct 2010, muravev at yandex dot ru wrote:

 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874
 
 --- Comment #9 from Ilya Murav'jov muravev at yandex dot ru 2010-10-06 
 19:43:30 UTC ---
 I've come across another weird warning emission in g++ 4.4:
 
 $ cat test.cc
 #include new
 struct interface_type {
 
 virtual interface_type* clone(void* storage) const
 {
 return ::new (storage) interface_type();
 }
 };
 
 struct poly_base {
 
 poly_base(const interface_type x) { x.clone(data); }
 
 typedef char storage_t[100];
 storage_t data;
 };
 
 struct instance_t: interface_type {};
 
 int main()
 {
 instance_t pi;
 poly_base p1(pi);
 
 interface_type* ptr = (interface_type*)(p1.data);
 poly_base p2(*ptr);
 }
 $ g++ -O3 -Wstrict-aliasing test.cc -o /dev/null
 test.cc: In function ‘int main()’:
 test.cc:12: warning: dereferencing pointer ‘ptr’ does break strict-aliasing
 rules
 test.cc:25: note: initialized from here
 
 $ g++ -v
 Using built-in specs.
 Target: i486-linux-gnu
 Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu9'
 --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
 --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
 --enable-multiarch --enable-linker-build-id --with-system-zlib
 --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
 --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
 --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
 --enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic
 --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
 --target=i486-linux-gnu
 Thread model: posix
 gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9)
 
 I get this only in g++ 4.4, g++ 4.5 does not warn.
 
 I want to note that this is a different type of warning about strict-aliasing
 rules, likely a more serious one. Can anyone tell what a difference between
 warning: dereferencing type-punned pointer will break strict-aliasing rules
 and warning: dereferencing pointer ‘ptr’ does break strict-aliasing rules?

The latter means that when doing pointer analysis GCC pruned all 
pointed-to objects using TBAA so the pointer ended up pointing to
nothing (but still was dereferenced).  The good news for you is that
GCC will assume the pointer points to anything in that case, not
nothing.

In GCC 4.5 points-to analysis doesn't use TBAA to prune the sets anymore
(because its fundamentally wrong), so the code emitting the warning
was removed.

Richard.

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[muravev at yandex dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

--- Comment #7 from Ilya Murav'jov muravev at yandex dot ru 2010-10-05 
00:10:20 UTC ---
AFAIK, users of Boost.Function suffer from this PR too.
https://svn.boost.org/trac/boost/ticket/4538

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[fw at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

Florian Weimer fw at gcc dot gnu.org changed:

   What|Removed |Added

 CC||fw at gcc dot gnu.org

--- Comment #8 from Florian Weimer fw at gcc dot gnu.org 2010-10-05 04:48:54 
UTC ---
(In reply to comment #6)

 The general problem is that alias analysis is hard, thus follows that proper
 warnings are equally hard.

Note that it says will break strict-aliasing rules, not might break
strict-aliasing rules (which also exists). I think the user can reasonably
expect that the will break variant is actually true.

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[fw at deneb dot enyo dot de]

--- Comment #5 from fw at deneb dot enyo dot de  2010-01-31 09:38 ---
Isn't this a wrong-code bug?  Or is the information used for the diagnostic not
used by the optimizers?


-- 

fw at deneb dot enyo dot de changed:

   What|Removed |Added

 CC||fw at deneb dot enyo dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[rguenth at gcc dot gnu dot org]

--- Comment #6 from rguenth at gcc dot gnu dot org  2010-01-31 11:17 ---
(In reply to comment #5)
 Isn't this a wrong-code bug?  Or is the information used for the diagnostic 
 not
 used by the optimizers?

The diagnostics are independent on the optimizers, the one diagnostic that
isn't (that is emitted from the optimizer itself) causes the optimizer to
not optimize (well, because it saw the problem and thus there is no point
in breaking things just because we can).

The general problem is that alias analysis is hard, thus follows that proper
warnings are equally hard.  All warnings we emit are either possible false
positives or if they are not the optimizers will not miscompile your code
because they know there is an alias even though type-based analysis says
there is not (well, this is exactly the case you want to warn about, but
as analysis is hard once you can tell you can as well not exploit the
mis-optimization opportunity).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[pinskia at gcc dot gnu dot org]

--- Comment #1 from pinskia at gcc dot gnu dot org  2009-11-06 09:09 ---
4.5 also fails and I cannot figure why if I do:
#include new
struct APInt {
int i;
};
int main() {
APInt I;
void *d;
char Data[sizeof(APInt)];
new((void*)Data)APInt();
d = Data;
*(APInt*)d = I;
}

GCC does not warn.


-- 

pinskia at gcc dot gnu dot org changed:

   What|Removed |Added

 CC||rguenth at gcc dot gnu dot
   ||org
 Status|UNCONFIRMED |NEW
 Ever Confirmed|0   |1
  Known to fail||4.5.0
   Last reconfirmed|-00-00 00:00:00 |2009-11-06 09:09:42
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[rguenther at suse dot de]

--- Comment #2 from rguenther at suse dot de  2009-11-06 09:16 ---
Subject: Re:  Incorrect dereferencing type-punned pointer
 will break strict-aliasing rules warning

On Fri, 6 Nov 2009, pinskia at gcc dot gnu dot org wrote:

 --- Comment #1 from pinskia at gcc dot gnu dot org  2009-11-06 09:09 
 ---
 4.5 also fails and I cannot figure why if I do:

fails?

 #include new
 struct APInt {
 int i;
 };
 int main() {
 APInt I;
 void *d;
 char Data[sizeof(APInt)];
 new((void*)Data)APInt();
 d = Data;
 *(APInt*)d = I;
 }
 
 GCC does not warn.

Of course not - the code is perfectly valid (apart from Data
not having suitable alignment for APInt, but that's unrelated
to aliasing issues).

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[pinskia at gcc dot gnu dot org]

--- Comment #3 from pinskia at gcc dot gnu dot org  2009-11-06 09:18 ---
  --- Comment #1 from pinskia at gcc dot gnu dot org  2009-11-06 09:09 
  ---
  4.5 also fails 

Fails in that it warns still.

The first example warns with 4.5, while adding an extra variable and doing a
cast to void* causes GCC not to warn.  


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

[Bug c++/41874] Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[rguenth at gcc dot gnu dot org]

--- Comment #4 from rguenth at gcc dot gnu dot org  2009-11-06 09:20 ---
Btw, this warning is emitted from the frontend which only warns if it sees
the address of an object casted, not random pointers (because of the
many false positives).  The frontend code also has no idea of the concept
of a dynamic type.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

[Bug c/41673] [4.5 Regression] variable-length array dereference inside sizeof gives warning: dereferencing type-punned pointer will break strict-aliasing rules

[hjl at gcc dot gnu dot org]

--- Comment #4 from hjl at gcc dot gnu dot org  2009-10-30 16:05 ---
Subject: Bug 41673

Author: hjl
Date: Fri Oct 30 16:04:41 2009
New Revision: 153759

URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=153759
Log:
2009-10-30  H.J. Lu  hongjiu...@intel.com

Backport from mainline:
2009-10-30  Dodji Seketeli  do...@redhat.com

PR c++/41863
* g++.dg/template/sizeof12.C: New test.

2009-10-29  Martin Jambor  mjam...@suse.cz

PR tree-optimization/41775
* g++.dg/torture/pr41775.C: New testcase.

2009-10-28  Jakub Jelinek  ja...@redhat.com

PR debug/41801
* g++.dg/ext/sync-3.C: New test.

2009-10-27  Jakub Jelinek  ja...@redhat.com

PR c++/41020
* g++.dg/lookup/extern-c-redecl5.C: Fix up regexp.

2009-10-26  Jakub Jelinek  ja...@redhat.com

PR bootstrap/41345
* gcc.dg/pr41345.c: New test.

2009-10-26  Dodji Seketeli  do...@redhat.com

PR c++/41785
* g++.dg/cpp0x/variadic96.C: New test.

2009-10-26  Dodji Seketeli  do...@redhat.com

PR c++/41020
* g++.dg/lookup/extern-c-redecl2.C: New test.
* g++.dg/lookup/extern-c-redecl3.C: Likewise.
* g++.dg/lookup/extern-c-redecl4.C: Likewise.
* g++.dg/lookup/extern-c-redecl5.C: Likewise.

2009-10-23  Joseph Myers  jos...@codesourcery.com

PR c/40033
* gcc.dg/noncompile/pr40033-1.c: New test.

2009-10-23  Joseph Myers  jos...@codesourcery.com

PR c/41673
* gcc.dg/Wstrict-aliasing-bogus-vla-1.c: New test.

2009-10-21  Sebastian Pop  sebastian@amd.com

PR tree-optimization/41497
* gcc.dg/tree-ssa/pr41497.c: New.

Added:
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/cpp0x/variadic96.C
  - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/cpp0x/variadic96.C
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/ext/sync-3.C
  - copied unchanged from r153757, trunk/gcc/testsuite/g++.dg/ext/sync-3.C
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl2.C
  - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl2.C
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl3.C
  - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl3.C
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl4.C
  - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl4.C
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl5.C
  - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl5.C
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/template/sizeof12.C
  - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/template/sizeof12.C
branches/gcc-4_4-branch/gcc/testsuite/g++.dg/torture/pr41775.C
  - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/torture/pr41775.C
branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-vla-1.c
  - copied unchanged from r153758,
trunk/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-vla-1.c
branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/noncompile/pr40033-1.c
  - copied unchanged from r153758,
trunk/gcc/testsuite/gcc.dg/noncompile/pr40033-1.c
branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/pr41345.c
  - copied unchanged from r153757, trunk/gcc/testsuite/gcc.dg/pr41345.c
branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/tree-ssa/pr41497.c
  - copied unchanged from r153758,
trunk/gcc/testsuite/gcc.dg/tree-ssa/pr41497.c
Modified:
branches/gcc-4_4-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41673

[Bug c++/41874] New: Incorrect dereferencing type-punned pointer will break strict-aliasing rules warning

[jyasskin at gmail dot com]

$ cat test.cc
#include new
struct APInt {
int i;
};
int main() {
APInt I;
char Data[sizeof(APInt)];
new((void*)Data)APInt();
*(APInt*)Data = I;
}
$ g++ -O3 -Wstrict-aliasing test.cc -o /dev/null
test.cc: In function 'int main()':
test.cc:9: warning: dereferencing type-punned pointer will break
strict-aliasing rules
test.cc:9: warning: dereferencing type-punned pointer will break
strict-aliasing rules

$ g++ -v
Using built-in specs.
Target: i386-apple-darwin9
Configured with: ../gcc-4.4.1/configure --prefix=/opt/local
--build=i386-apple-darwin9 --enable-languages=c,c++,objc,obj-c++,java,fortran
--libdir=/opt/local/lib/gcc44 --includedir=/opt/local/include/gcc44
--infodir=/opt/local/share/info --mandir=/opt/local/share/man
--with-local-prefix=/opt/local --with-system-zlib --disable-nls
--program-suffix=-mp-4.4 --with-gxx-include-dir=/opt/local/include/gcc44/c++/
--with-gmp=/opt/local --with-mpfr=/opt/local
Thread model: posix
gcc version 4.4.1 (GCC) 


The warning goes away if I change *(APInt*)Data = I; to *(APInt*)(void*)Data
= I; even though an extra cast through void* can't improve the situation wrt
strict-aliasing.


-- 
   Summary: Incorrect dereferencing type-punned pointer will break
strict-aliasing rules warning
   Product: gcc
   Version: 4.4.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jyasskin at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41874

[Bug c/41673] [4.5 Regression] variable-length array dereference inside sizeof gives warning: dereferencing type-punned pointer will break strict-aliasing rules

[jsm28 at gcc dot gnu dot org]

--- Comment #2 from jsm28 at gcc dot gnu dot org  2009-10-23 12:18 ---
Subject: Bug 41673

Author: jsm28
Date: Fri Oct 23 12:18:42 2009
New Revision: 153496

URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=153496
Log:
PR c/41673
* alias.c (get_alias_set): Call langhook before returning 0 for
types with structural equality.
* c-common.c (c_common_get_alias_set): Use alias set of element
type for arrays with structural comparison.

testsuite:
* gcc.dg/Wstrict-aliasing-bogus-vla-1.c: New test.

Added:
trunk/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-vla-1.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/alias.c
trunk/gcc/c-common.c
trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41673

[Bug c/41673] [4.5 Regression] variable-length array dereference inside sizeof gives warning: dereferencing type-punned pointer will break strict-aliasing rules

[jsm28 at gcc dot gnu dot org]

--- Comment #3 from jsm28 at gcc dot gnu dot org  2009-10-23 12:23 ---
Fixed for 4.5.


-- 

jsm28 at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
  Known to work||4.5.0
 Resolution||FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41673

[Bug c/41673] [4.5 Regression] variable-length array dereference inside sizeof gives warning: dereferencing type-punned pointer will break strict-aliasing rules

[jsm28 at gcc dot gnu dot org]

--- Comment #1 from jsm28 at gcc dot gnu dot org  2009-10-23 01:03 ---
Testing a patch.


-- 

jsm28 at gcc dot gnu dot org changed:

   What|Removed |Added

 AssignedTo|unassigned at gcc dot gnu   |jsm28 at gcc dot gnu dot org
   |dot org |
 Status|UNCONFIRMED |ASSIGNED
 Ever Confirmed|0   |1
   Last reconfirmed|-00-00 00:00:00 |2009-10-23 01:03:03
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41673

[Bug c/41673] New: 4.5.0 20091008 variable-length array dereference inside sizeof gives warning: dereferencing type-punned pointer will break strict-aliasing rules

[gmaxwell at gmail dot com]

A variable-length array pointer 'dereference' inside sizeof() is causing GCC to
give an aliasing warning. I can think of no reason why completely
compiletime-static sizeof() activity could create an aliasing violation.

I've included a contrived example showing 4.5.0 producing the warning while
4.4.1 does not complain:

[gmaxw...@floodlamp tmp]$ cat test.c
#include string.h
int main(int argc, char *argv[])
{
float x[argc];
float y[argc];
return NULL == memcpy(y, x, argc * sizeof(*x));
}
[gmaxw...@floodlamp tmp]$ /usr/local/bin/gcc -std=gnu99 -O2 -Wall -o test
test.c
test.c: In function ‘main’:
test.c:6:5: warning: dereferencing type-punned pointer will break
strict-aliasing rules
[gmaxw...@floodlamp tmp]$ /usr/local/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/usr/local/bin/gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-unknown-linux-gnu/4.5.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ./configure --with-ppl --with-cloog --with-gmp --enable-lto
Thread model: posix
gcc version 4.5.0 20091008 (experimental) (GCC) 
[gmaxw...@floodlamp tmp]$ /usr/bin/gcc -std=gnu99 -O2 -Wall -o test test.c
[gmaxw...@floodlamp tmp]$ /usr/bin/gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i586
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.4.1 20090725 (Red Hat 4.4.1-2) (GCC) 

The -O2 plus sizeof(*x) anywhere where x is a var-array is necessary and
sufficient to trigger this. Switching to a statically sized array avoids the
warning.

The actual use-case where I hit this is where sizeof() is used in this manner
when a type is selected by some compile time configuration and manually
restating the type in sizeof() would require a great many more ifdefs.


-- 
   Summary: 4.5.0 20091008 variable-length array dereference inside
sizeof gives warning: dereferencing type-punned pointer
will break strict-aliasing rules
   Product: gcc
   Version: 4.5.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gmaxwell at gmail dot com
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41673

[Bug c/41673] [4.5 Regression] variable-length array dereference inside sizeof gives warning: dereferencing type-punned pointer will break strict-aliasing rules

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

   What|Removed |Added

   Keywords||diagnostic
Summary|4.5.0 20091008 variable-|[4.5 Regression] variable-
   |length array dereference|length array dereference
   |inside sizeof gives |inside sizeof gives
   |warning: dereferencing |warning: dereferencing
   |type-punned pointer will|type-punned pointer will
   |break strict-aliasing rules|break strict-aliasing rules
   Target Milestone|--- |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41673

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[pcarlini at suse dot de]

--- Comment #7 from pcarlini at suse dot de  2007-11-11 14:04 ---
*** Bug 34066 has been marked as a duplicate of this bug. ***


-- 

pcarlini at suse dot de changed:

   What|Removed |Added

 CC||guillaume dot melquiond at
   ||ens-lyon dot fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[jakub at gcc dot gnu dot org]

--- Comment #4 from jakub at gcc dot gnu dot org  2007-11-01 11:57 ---
Testing a fix.


-- 

jakub at gcc dot gnu dot org changed:

   What|Removed |Added

 AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
   |dot org |
 Status|NEW |ASSIGNED
   Last reconfirmed|2007-06-11 21:19:44 |2007-11-01 11:57:35
   date||


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[jakub at gcc dot gnu dot org]

--- Comment #5 from jakub at gcc dot gnu dot org  2007-11-01 22:50 ---
Subject: Bug 32260

Author: jakub
Date: Thu Nov  1 22:50:32 2007
New Revision: 129835

URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=129835
Log:
PR c++/32260
* rtti.c (enum_tinfo_kind): Fix TK_TYPE_INFO_TYPE comment.
(typeid_ok_p): Use the same alias set for abi::__type_info_pseudo
as for std::type_info.

* g++.dg/rtti/typeid7.C: New test.

Added:
trunk/gcc/testsuite/g++.dg/rtti/typeid7.C
Modified:
trunk/gcc/cp/ChangeLog
trunk/gcc/cp/rtti.c
trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[jakub at gcc dot gnu dot org]

--- Comment #6 from jakub at gcc dot gnu dot org  2007-11-01 23:09 ---
Fixed.


-- 

jakub at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution||FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[pcarlini at suse dot de]

--- Comment #3 from pcarlini at suse dot de  2007-10-26 09:00 ---
*** Bug 33902 has been marked as a duplicate of this bug. ***


-- 

pcarlini at suse dot de changed:

   What|Removed |Added

 CC||benoit dot hudson at gmail
   ||dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[pcarlini at suse dot de]

--- Comment #2 from pcarlini at suse dot de  2007-09-28 17:04 ---
Short term at least, could be considered a duplicate of PR32256 (and PR32368).


-- 

pcarlini at suse dot de changed:

   What|Removed |Added

 CC||pcarlini at suse dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

   What|Removed |Added

   Priority|P3  |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] [4.3 Regression] too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[pinskia at gcc dot gnu dot org]

--- Comment #1 from pinskia at gcc dot gnu dot org  2007-06-11 21:19 ---
Confirmed, I have not looked into this close enough but this is a front-end bug
as the type (and aliasing set) of the typeid variable is different from
std::type_info's.


-- 

pinskia at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
 Ever Confirmed|0   |1
   Keywords||alias, diagnostic
   Last reconfirmed|-00-00 00:00:00 |2007-06-11 21:19:44
   date||
Summary|too many warning:   |[4.3 Regression] too many
   |dereferencing type-punned   |warning: dereferencing type-
   |pointer will break strict-  |punned pointer will break
   |aliasing rules  |strict-aliasing rules
   Target Milestone|--- |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260

[Bug c++/32260] New: too many warning: dereferencing type-punned pointer will break strict-aliasing rules

[sylvain dot pion at sophia dot inria dot fr]

The following code, compiled with -O2 -Wall (g++ 4.3 as of 20070607),
produces the following unexpected/annoying warning:

test_typeinfo.cpp: In function 'int main()':
test_typeinfo.cpp:5: warning: dereferencing type-punned pointer will break
strict-aliasing rules
test_typeinfo.cpp:5: warning: unused variable 't'


~ cat test_typeinfo.cpp 
#include typeinfo

int main()
{
  const std::type_info  t = typeid(int);
}


Is this really meant to warn for such a code???


-- 
   Summary: too many warning: dereferencing type-punned pointer will
break strict-aliasing rules
   Product: gcc
   Version: 4.3.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sylvain dot pion at sophia dot inria dot fr
  GCC host triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32260