[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 Richard Biener rguenth at gcc dot gnu.org changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED Target Milestone|4.9.1 |4.9.0 --- Comment #28 from Richard Biener rguenth at gcc dot gnu.org --- Fixed for 4.9.0.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #27 from Richard Biener rguenth at gcc dot gnu.org --- Author: rguenth Date: Mon Apr 28 14:36:13 2014 New Revision: 209863 URL: http://gcc.gnu.org/viewcvs?rev=209863root=gccview=rev Log: 2014-04-28 Richard Biener rguent...@suse.de PR middle-end/60092 * builtins.def (DEF_C11_BUILTIN): Add. (BUILT_IN_ALIGNED_ALLOC): Likewise. * coretypes.h (enum function_class): Add function_c11_misc. * tree-ssa-alias.c (ref_maybe_used_by_call_p_1): Handle BUILT_IN_ALIGNED_ALLOC like BUILT_IN_MALLOC. (call_may_clobber_ref_p_1): Likewise. * tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Likewise. (mark_all_reaching_defs_necessary_1): Likewise. (propagate_necessity): Likewise. (eliminate_unnecessary_stmts): Likewise. * tree-ssa-ccp.c (evaluate_stmt): Handle BUILT_IN_ALIGNED_ALLOC. ada/ * gcc-interface/utils.c: Define flag_isoc11. lto/ * lto-lang.c: Define flag_isoc11. * gcc.dg/tree-ssa/alias-32.c: New testcase. * gcc.dg/vect/pr60092.c: Likewise. Added: trunk/gcc/testsuite/gcc.dg/tree-ssa/alias-32.c trunk/gcc/testsuite/gcc.dg/vect/pr60092.c Modified: trunk/gcc/ChangeLog trunk/gcc/ada/ChangeLog trunk/gcc/ada/gcc-interface/utils.c trunk/gcc/builtins.def trunk/gcc/coretypes.h trunk/gcc/lto/ChangeLog trunk/gcc/lto/lto-lang.c trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-alias.c trunk/gcc/tree-ssa-ccp.c trunk/gcc/tree-ssa-dce.c
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added Target Milestone|4.9.0 |4.9.1 --- Comment #26 from Jakub Jelinek jakub at gcc dot gnu.org --- GCC 4.9.0 has been released
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #25 from ro at CeBiTec dot Uni-Bielefeld.DE ro at CeBiTec dot Uni-Bielefeld.DE --- --- Comment #24 from Richard Biener rguenth at gcc dot gnu.org --- As the standard doesn't specify that the value is undefined upon error and it only specifies its contents upon successfull completion it implicitely says that it retains the previous value on error. I'd say xfail/skip this on solaris11 and report a bug to them. Patch here: http://gcc.gnu.org/ml/gcc-patches/2014-02/msg01039.html I'd already reported the bug: 18253126 posix_memalign writes to first arg on error Rainer
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #24 from Richard Biener rguenth at gcc dot gnu.org --- As the standard doesn't specify that the value is undefined upon error and it only specifies its contents upon successfull completion it implicitely says that it retains the previous value on error. I'd say xfail/skip this on solaris11 and report a bug to them.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 Rainer Orth ro at gcc dot gnu.org changed: What|Removed |Added CC||ro at gcc dot gnu.org Target Milestone|--- |4.9.0 --- Comment #21 from Rainer Orth ro at gcc dot gnu.org --- The new test FAILs on Solaris 11 (both SPARC and x86), which, unlike Solaris 10, has posix_memalign in libc: FAIL: gcc.dg/torture/pr60092.c -O0 execution test The posix_memalign invocation with size = -1 cannot be right, and indeed the function returns ENOMEM. Rainer
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #22 from Jakub Jelinek jakub at gcc dot gnu.org --- (In reply to Rainer Orth from comment #21) The new test FAILs on Solaris 11 (both SPARC and x86), which, unlike Solaris 10, has posix_memalign in libc: FAIL: gcc.dg/torture/pr60092.c -O0 execution test The posix_memalign invocation with size = -1 cannot be right, and indeed the function returns ENOMEM. The invocation uses size -1 intentionally, and expects ENOMEM, but if Solaris libc stores to what the first argument points to even when it fails, then it violates POSIX.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #23 from ro at CeBiTec dot Uni-Bielefeld.DE ro at CeBiTec dot Uni-Bielefeld.DE --- --- Comment #22 from Jakub Jelinek jakub at gcc dot gnu.org --- (In reply to Rainer Orth from comment #21) The new test FAILs on Solaris 11 (both SPARC and x86), which, unlike Solaris 10, has posix_memalign in libc: FAIL: gcc.dg/torture/pr60092.c -O0 execution test The posix_memalign invocation with size = -1 cannot be right, and indeed the function returns ENOMEM. The invocation uses size -1 intentionally, and expects ENOMEM, but if Solaris libc stores to what the first argument points to even when it fails, then it violates POSIX. POSIX.1 doesn't explicitly forbid setting *memptr on error: http://pubs.opengroup.org/onlinepubs/007904975/functions/posix_memalign.html But I agree it seems strange, and in the OpenSolaris sources you see that *memptr is set to the memalign() return value (NULL in this case). Rainer
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 Tobias Burnus burnus at gcc dot gnu.org changed: What|Removed |Added CC||burnus at gcc dot gnu.org --- Comment #18 from Tobias Burnus burnus at gcc dot gnu.org --- (In reply to Richard Biener from comment #1) We could lower posix_memalign (ptr, align, size); to posix_memalign (ptr, align, size); ptr = __builtin_assume_algined (ptr, align); and hope for FRE to fix things up enough to make that useful. I wonder about mm_malloc. I assume for config/i386/pmm_malloc.h, it is already handled via posix_memalign, but shouldn't one also handle config/i386/gmm_malloc.h? For instance via --- a/gcc/config/i386/gmm_malloc.h +++ b/gcc/config/i386/gmm_malloc.h @@ -61,7 +61,11 @@ _mm_malloc (size_t size, size_t align) /* Store the original pointer just before p. */ ((void **) aligned_ptr) [-1] = malloc_ptr; +#if defined(__GNUC__) __GNUC__ = 4 __GNUC_MINOR__ = 7 + return __builtin_assume_aligned(aligned_ptr, align); +#else return aligned_ptr; +#endif } static __inline__ void
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #19 from Jakub Jelinek jakub at gcc dot gnu.org --- (In reply to Tobias Burnus from comment #18) (In reply to Richard Biener from comment #1) We could lower posix_memalign (ptr, align, size); to posix_memalign (ptr, align, size); ptr = __builtin_assume_algined (ptr, align); and hope for FRE to fix things up enough to make that useful. I wonder about mm_malloc. I assume for config/i386/pmm_malloc.h, it is already handled via posix_memalign, but shouldn't one also handle config/i386/gmm_malloc.h? For instance via --- a/gcc/config/i386/gmm_malloc.h +++ b/gcc/config/i386/gmm_malloc.h @@ -61,7 +61,11 @@ _mm_malloc (size_t size, size_t align) /* Store the original pointer just before p. */ ((void **) aligned_ptr) [-1] = malloc_ptr; +#if defined(__GNUC__) __GNUC__ = 4 __GNUC_MINOR__ = 7 + return __builtin_assume_aligned(aligned_ptr, align); +#else return aligned_ptr; +#endif } static __inline__ void No, why? ccp of course understands the dynamic realignment: aligned_ptr = (void *) (((size_t) malloc_ptr + align) ~((size_t) (align) - 1)); so will know that aligned_ptr is align bytes aligned.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #20 from Richard Biener rguenth at gcc dot gnu.org --- Author: rguenth Date: Wed Feb 12 13:36:08 2014 New Revision: 207720 URL: http://gcc.gnu.org/viewcvs?rev=207720root=gccview=rev Log: 2014-02-12 Richard Biener rguent...@suse.de PR middle-end/60092 * gimple-low.c (lower_builtin_posix_memalign): Lower conditional of posix_memalign being successful. (lower_stmt): Restrict lowering of posix_memalign to when -ftree-bit-ccp is enabled. * gcc.dg/torture/pr60092.c: New testcase. * gcc.dg/tree-ssa/alias-31.c: Disable SRA. Added: trunk/gcc/testsuite/gcc.dg/torture/pr60092.c Modified: trunk/gcc/ChangeLog trunk/gcc/gimple-low.c trunk/gcc/testsuite/ChangeLog trunk/gcc/testsuite/gcc.dg/tree-ssa/alias-31.c
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #17 from Jakub Jelinek jakub at gcc dot gnu.org --- Author: jakub Date: Sat Feb 8 09:09:01 2014 New Revision: 207628 URL: http://gcc.gnu.org/viewcvs?rev=207628root=gccview=rev Log: PR middle-end/60092 * tree-ssa-ccp.c (surely_varying_stmt_p): Don't return true if TYPE_ATTRIBUTES (gimple_call_fntype ()) contain assume_aligned or alloc_align attributes. (bit_value_assume_aligned): Add ATTR, PTRVAL and ALLOC_ALIGN arguments. Handle also assume_aligned and alloc_align attributes. (evaluate_stmt): Adjust bit_value_assume_aligned caller. Handle calls to functions with assume_aligned or alloc_align attributes. * doc/extend.texi: Document assume_aligned and alloc_align attributes. c-family/ * c-common.c (handle_alloc_size_attribute): Use tree_fits_uhwi_p and tree_to_uhwi. (handle_alloc_align_attribute, handle_assume_aligned_attribute): New functions. (c_common_attribute_table): Add alloc_align and assume_aligned attributes. testsuite/ * gcc.dg/attr-alloc_align-1.c: New test. * gcc.dg/attr-alloc_align-2.c: New test. * gcc.dg/attr-alloc_align-3.c: New test. * gcc.dg/attr-assume_aligned-1.c: New test. * gcc.dg/attr-assume_aligned-2.c: New test. * gcc.dg/attr-assume_aligned-3.c: New test. Added: trunk/gcc/testsuite/gcc.dg/attr-alloc_align-1.c trunk/gcc/testsuite/gcc.dg/attr-alloc_align-2.c trunk/gcc/testsuite/gcc.dg/attr-alloc_align-3.c trunk/gcc/testsuite/gcc.dg/attr-assume_aligned-1.c trunk/gcc/testsuite/gcc.dg/attr-assume_aligned-2.c trunk/gcc/testsuite/gcc.dg/attr-assume_aligned-3.c Modified: trunk/gcc/ChangeLog trunk/gcc/c-family/ChangeLog trunk/gcc/c-family/c-common.c trunk/gcc/doc/extend.texi trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-ccp.c
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #15 from Richard Biener rguenth at gcc dot gnu.org --- Author: rguenth Date: Fri Feb 7 09:33:23 2014 New Revision: 207595 URL: http://gcc.gnu.org/viewcvs?rev=207595root=gccview=rev Log: 2014-02-07 Richard Biener rguent...@suse.de PR middle-end/60092 * builtin-types.def (BT_FN_INT_PTRPTR_SIZE_SIZE): Add. * builtins.def (BUILT_IN_POSIX_MEMALIGN): Likewise. * tree-ssa-structalias.c (find_func_aliases_for_builtin_call): Handle BUILT_IN_POSIX_MEMALIGN. (find_func_clobbers): Likewise. * tree-ssa-alias.c (ref_maybe_used_by_call_p_1): Likewise. (call_may_clobber_ref_p_1): Likewise. * gcc.dg/tree-ssa/alias-30.c: New testcase. * gcc.dg/tree-ssa/alias-31.c: Likewise. Added: trunk/gcc/testsuite/gcc.dg/tree-ssa/alias-30.c trunk/gcc/testsuite/gcc.dg/tree-ssa/alias-31.c Modified: trunk/gcc/ChangeLog trunk/gcc/builtin-types.def trunk/gcc/builtins.def trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-alias.c trunk/gcc/tree-ssa-structalias.c
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #16 from Richard Biener rguenth at gcc dot gnu.org --- Author: rguenth Date: Fri Feb 7 13:41:10 2014 New Revision: 207598 URL: http://gcc.gnu.org/viewcvs?rev=207598root=gccview=rev Log: 2014-02-07 Richard Biener rguent...@suse.de PR middle-end/60092 * gimple-low.c (lower_builtin_posix_memalign): New function. (lower_stmt): Call it to lower posix_memalign in a way to make alignment info accessible. * gcc.dg/vect/pr60092-2.c: New testcase. Added: trunk/gcc/testsuite/gcc.dg/vect/pr60092-2.c Modified: trunk/gcc/ChangeLog trunk/gcc/gimple-low.c trunk/gcc/testsuite/ChangeLog
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 Richard Biener rguenth at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |ASSIGNED Last reconfirmed||2014-02-06 Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org Ever confirmed|0 |1 --- Comment #1 from Richard Biener rguenth at gcc dot gnu.org --- As of posix_memalign the issue is not so much that of alias analysis (we could handle it but we don't have a builtin right now) but that of alignment analysis which doesn't implement alignment tracking of pointers stored in memory. We could lower posix_memalign (ptr, align, size); to posix_memalign (ptr, align, size); ptr = __builtin_assume_algined (ptr, align); and hope for FRE to fix things up enough to make that useful.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
Jakub Jelinek jakub at gcc dot gnu.org changed:
What|Removed |Added
CC||jakub at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek jakub at gcc dot gnu.org ---
Well, the problem with doing it this way is that ptr is still considered
address taken and the assume aligned then really can result in a noop move.
What I meant is expand:
ret = posix_memalign (ptr, align, size);
as
{
void *temp;
ret = posix_memalign (temp, align, size);
void *temp2 = __builtin_passthru_attribute_malloc_size (temp, size);
ptr = __typeof (ptr) __builtin_assume_aligned (temp2, align);
temp ={v}{CLOBBER};
}
The advantages of doing it this way would be that (if ptr is not address taken
for other reasons) that it would not need to be address taken, escape and all
the like, I think posix_memalign is not reading the old content of the pointer
nor storing it anywhere, it just fills it in as another result, just by
reference.
And the optimizers would know it doesn't alias anything, like if it came from
malloc (size);, and is aligned to align bytes at least.
The disadvantage would be that if ptr is addressable for other reasons, we
wouldn't reuse it's address for posix_memalign, but pass address of another
temporary and then copied the mem.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #3 from Richard Biener rguenth at gcc dot gnu.org --- Created attachment 32064 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=32064action=edit part #1, aliasing I've implemented the aliasing parts (and the builtin obviously). It's true that doing posix_memalign (ptr, ); ptr = __builtin_assume_aligned (ptr, ...); will keep ptr address-taken - but isn't it kept address-taken anyway because it's passed to posix_memalign? I think you are mixing the possible optimization we can do to posix_memalign in general with the alignment issue, no? Thus, we could transform posix_memalign (ptr, ); to void *tem; posix_memalign (tem, ); ptr = tem; independently. Doing it as part of the alignment stuff of course makes sense. But as you say, eventually we'd just use an extra stack slot for no good reason. I've long thought of teaching some more tricks to update_address_taken - basically ignore some of the address-takens and apply simple transforms on the stmts causing them if that would make the var non-address-taken (memcpy comes to my mind as well here).
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #4 from Marc Glisse glisse at gcc dot gnu.org --- Hack: when the return value of posix_memalign is ignored, if the platform supports it, replace with a call to aligned_alloc (C11), which has an easier interface.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #5 from Richard Biener rguenth at gcc dot gnu.org --- Created attachment 32066 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=32066action=edit part #2, C11 aligned_alloc It was noted that aligned_alloc is standard enough to be supported (and with nicer interface albeit possibly clobbering errno ...).
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
--- Comment #6 from Jakub Jelinek jakub at gcc dot gnu.org ---
(In reply to Marc Glisse from comment #4)
Hack: when the return value of posix_memalign is ignored, if the platform
supports it, replace with a call to aligned_alloc (C11), which has an easier
interface.
The question is if posix_memalign is allowed to change errno. If it is, then
making glibc contains say something like:
extern int __REDIRECT_NTH (__posix_memalign_alias,
(void ** __ptr, size_t __alignment, size_t __size),
posix_memalign) __nonnull ((1)) __wur;
extern void *__REDIRECT_NTH (__memalign_alias,
(size_t __alignment, size_t __size),
memalign) __attribute__ ((__malloc__,
__alloc_size__ (2)));
__extern_inline int
posix_memalign (void **__ptr, size_t __alignment, size_t __size)
{
if (__builtin_constant_p (__alignment))
{
if (__alignment == 0
|| __alignment (__alignment - 1)) != 0
|| __alignment % sizeof (void *))
return EINVAL;
void *__res = __memalign_alias (__alignment, __size);
if (__res == NULL)
return ENOMEM;
*__ptr = __res;
return 0;
}
return __posix_memalign_alias (__ptr, __alignment, __size);
}
But looking at glibc sources, even posix_memalign actually changes errno.
Tbe problem with this inline version is that user aliasing bugs will trigger
people more often, and that some hack will need to be find out for the EINVAL
and ENOMEM values (because, stdlib.h is not supposed to include errno.h I
guess, so it would need to be some __EINVAL/__ENOMEM value determined by
configure or something).
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
--- Comment #7 from Richard Biener rguenth at gcc dot gnu.org ---
(In reply to Jakub Jelinek from comment #6)
(In reply to Marc Glisse from comment #4)
Hack: when the return value of posix_memalign is ignored, if the platform
supports it, replace with a call to aligned_alloc (C11), which has an easier
interface.
The question is if posix_memalign is allowed to change errno. If it is,
then making glibc contains say something like:
extern int __REDIRECT_NTH (__posix_memalign_alias,
(void ** __ptr, size_t __alignment, size_t
__size),
posix_memalign) __nonnull ((1)) __wur;
extern void *__REDIRECT_NTH (__memalign_alias,
(size_t __alignment, size_t __size),
memalign) __attribute__ ((__malloc__,
__alloc_size__ (2)));
__extern_inline int
posix_memalign (void **__ptr, size_t __alignment, size_t __size)
{
if (__builtin_constant_p (__alignment))
{
if (__alignment == 0
|| __alignment (__alignment - 1)) != 0
|| __alignment % sizeof (void *))
return EINVAL;
void *__res = __memalign_alias (__alignment, __size);
if (__res == NULL)
return ENOMEM;
*__ptr = __res;
return 0;
}
return __posix_memalign_alias (__ptr, __alignment, __size);
}
But looking at glibc sources, even posix_memalign actually changes errno.
Tbe problem with this inline version is that user aliasing bugs will trigger
people more often, and that some hack will need to be find out for the
EINVAL and ENOMEM values (because, stdlib.h is not supposed to include
errno.h I guess, so it would need to be some __EINVAL/__ENOMEM value
determined by configure or something).
According to the specification this is wrong. Note that changing errno
is hindering optimization. For example
int foo (int *p)
{
*p = 1;
malloc (4);
return *p;
}
cannot CSE *p because p may point to errno. (works for float *p and
works when using posix_memalign with my patch)
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
--- Comment #8 from Jakub Jelinek jakub at gcc dot gnu.org ---
(In reply to Richard Biener from comment #7)
According to the specification this is wrong. Note that changing errno
is hindering optimization. For example
int foo (int *p)
{
*p = 1;
malloc (4);
return *p;
}
cannot CSE *p because p may point to errno. (works for float *p and
works when using posix_memalign with my patch)
Well, e.g.
http://pubs.opengroup.org/onlinepubs/007904975/functions/posix_memalign.html
says nothing about errno, I think only functions which explicitly document not
to clobber errno may not, all other functions may, but it's value is undefined
after the call. For calls that are documented to change errno in some cases,
it is again defined only if those calls return a particular value (e.g. -1),
otherwise errno is still undefined.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
--- Comment #9 from rguenther at suse dot de rguenther at suse dot de ---
On Thu, 6 Feb 2014, jakub at gcc dot gnu.org wrote:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092
--- Comment #8 from Jakub Jelinek jakub at gcc dot gnu.org ---
(In reply to Richard Biener from comment #7)
According to the specification this is wrong. Note that changing errno
is hindering optimization. For example
int foo (int *p)
{
*p = 1;
malloc (4);
return *p;
}
cannot CSE *p because p may point to errno. (works for float *p and
works when using posix_memalign with my patch)
Well, e.g.
http://pubs.opengroup.org/onlinepubs/007904975/functions/posix_memalign.html
says nothing about errno, I think only functions which explicitly document not
to clobber errno may not, all other functions may, but it's value is undefined
after the call. For calls that are documented to change errno in some cases,
it is again defined only if those calls return a particular value (e.g. -1),
otherwise errno is still undefined.
Ok, my manpage says
RETURN VALUE
aligned_alloc(), memalign(), valloc(), and pvalloc() return a
pointer
to the allocated memory, or NULL if the request fails.
posix_memalign() returns zero on success, or one of the error
values
listed in the next section on failure. Note that errno is not set.
so that must be incorrect.
If the value of errno is undefined after posix_memalign that doesn't
help us as we then still cannot CSE.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #10 from Jakub Jelinek jakub at gcc dot gnu.org --- (In reply to rguent...@suse.de from comment #9) Ok, my manpage says RETURN VALUE aligned_alloc(), memalign(), valloc(), and pvalloc() return a pointer to the allocated memory, or NULL if the request fails. posix_memalign() returns zero on success, or one of the error values listed in the next section on failure. Note that errno is not set. so that must be incorrect. If the value of errno is undefined after posix_memalign that doesn't help us as we then still cannot CSE. Linux man pages are often incorrect, better look at the 3p ones ;).
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #11 from Andreas Schwab sch...@linux-m68k.org --- If a function is not allowed to change errno this must be explicitly documented.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #12 from Richard Biener rguenth at gcc dot gnu.org --- (In reply to Andreas Schwab from comment #11) If a function is not allowed to change errno this must be explicitly documented. That means Index: gcc/tree-ssa-alias.c === --- gcc/tree-ssa-alias.c.orig 2014-02-06 15:43:42.138266256 +0100 +++ gcc/tree-ssa-alias.c2014-02-06 15:43:33.046266882 +0100 @@ -1847,7 +1847,9 @@ call_may_clobber_ref_p_1 (gimple call, a ao_ref dref; ao_ref_init_from_ptr_and_size (dref, ptrptr, TYPE_SIZE_UNIT (ptr_type_node)); - return refs_may_alias_p_1 (dref, ref, false); + return (refs_may_alias_p_1 (dref, ref, false) + || (flag_errno_math +targetm.ref_may_alias_errno (ref))); } /* Freeing memory kills the pointed-to memory. More importantly the call has to serve as a barrier for moving loads and stores is necessary.
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #13 from Jakub Jelinek jakub at gcc dot gnu.org --- (In reply to Richard Biener from comment #12) (In reply to Andreas Schwab from comment #11) If a function is not allowed to change errno this must be explicitly documented. That means Index: gcc/tree-ssa-alias.c === --- gcc/tree-ssa-alias.c.orig 2014-02-06 15:43:42.138266256 +0100 +++ gcc/tree-ssa-alias.c2014-02-06 15:43:33.046266882 +0100 @@ -1847,7 +1847,9 @@ call_may_clobber_ref_p_1 (gimple call, a ao_ref dref; ao_ref_init_from_ptr_and_size (dref, ptrptr, TYPE_SIZE_UNIT (ptr_type_node)); - return refs_may_alias_p_1 (dref, ref, false); + return (refs_may_alias_p_1 (dref, ref, false) + || (flag_errno_math +targetm.ref_may_alias_errno (ref))); } /* Freeing memory kills the pointed-to memory. More importantly the call has to serve as a barrier for moving loads and stores is necessary. For posix_memalign? I think errno can contain any value, except that library is not allowed to clear errno. So, IMHO *p = 1; posix_memalign (...); return *p; can be still optimized into return 1;, because if p = errno; then *p after the call has undefined value (just known not to be zero).
[Bug middle-end/60092] posix_memalign not recognized to derive alias and alignment info
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #14 from rguenther at suse dot de rguenther at suse dot de --- On Thu, 6 Feb 2014, jakub at gcc dot gnu.org wrote: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60092 --- Comment #13 from Jakub Jelinek jakub at gcc dot gnu.org --- (In reply to Richard Biener from comment #12) (In reply to Andreas Schwab from comment #11) If a function is not allowed to change errno this must be explicitly documented. That means Index: gcc/tree-ssa-alias.c === --- gcc/tree-ssa-alias.c.orig 2014-02-06 15:43:42.138266256 +0100 +++ gcc/tree-ssa-alias.c2014-02-06 15:43:33.046266882 +0100 @@ -1847,7 +1847,9 @@ call_may_clobber_ref_p_1 (gimple call, a ao_ref dref; ao_ref_init_from_ptr_and_size (dref, ptrptr, TYPE_SIZE_UNIT (ptr_type_node)); - return refs_may_alias_p_1 (dref, ref, false); + return (refs_may_alias_p_1 (dref, ref, false) + || (flag_errno_math +targetm.ref_may_alias_errno (ref))); } /* Freeing memory kills the pointed-to memory. More importantly the call has to serve as a barrier for moving loads and stores is necessary. For posix_memalign? I think errno can contain any value, except that library is not allowed to clear errno. So, IMHO *p = 1; posix_memalign (...); return *p; can be still optimized into return 1;, because if p = errno; then *p after the call has undefined value (just known not to be zero). But on allocation failure posix_memalign may set it to 2, no? So for errno = 0; posix_memalign () errno = 0; ptr = malloc (); if (!ptr) perror (); we may not DSE the 2nd errno = 0 store. Richard.
