On Tue, May 19, 2026 at 4:03 PM Jonathan Wakely <[email protected]> wrote:
> On Tue, 19 May 2026 at 11:57, Jonathan Wakely <[email protected]> > wrote: > > > > On Tue, 19 May 2026 at 10:29, Avi Kivity <[email protected]> wrote: > > > > > > > > > > > > On Tue, May 19, 2026 at 11:03 AM Avi Kivity <[email protected]> wrote: > > >> > > >> > > >> > > >> On Tue, May 19, 2026 at 2:22 AM <[email protected]> wrote: > > >>> > > >>> Dear contributor, > > >>> > > >>> Our automatic CI has detected problems related to your patch(es). > Please find some details below. > > >>> > > >>> In aarch64 native, after: > > >>> | commit gcc-17-570-g79e29562907b > > >>> | Author: Avi Kivity <[email protected]> > > >>> | Date: Thu Feb 26 19:59:41 2026 +0200 > > >>> | > > >>> | libstdc++: optimize std::uninitialized_move{,_n}() to memcpy > when possible [PR121789] > > >>> | > > >>> | std::uninitialized_move{,_n} delegates to the corresponding > > >>> | std::uninitialized_copy() variant after wrapping with a move > > >>> | iterator, but the std::uninitialized_copy() doesn't unwrap > the > > >>> | ... 17 lines of the commit log omitted. > > >>> > > >>> Produces 1 regression: > > >>> | > > >>> | regressions.sum: > > >>> | Running g++:g++.dg/torture/dg-torture.exp ... > > >>> | FAIL: g++.dg/torture/pr118521.C -O1 (test for excess errors) > > >> > > >> > > >> I'll take a look. > > > > > > > > > In file included from /mnt/gcc.bin/include/c++/17.0.0/vector:67, > > > from ./gcc/testsuite/g++.dg/torture/pr118521.C:5: > > > In function ‘_ForwardIterator > std::uninitialized_fill_n(_ForwardIterator, _Size, const _Tp&) [with > _ForwardIterator = char*; _Size = long unsigned int; _Tp = char]’, > > > inlined from ‘constexpr _ForwardIterator > std::__uninitialized_fill_n_a(_ForwardIterator, _Size, const _Tp&, > allocator<_Tp>&) [with _ForwardIterator = char*; _Size = long unsigned int; > _Tp = char; _Tp2 = char]’ at > /mnt/gcc.bin/include/c++/17.0.0/bits/stl_uninitialized.h:778:39, > > > inlined from ‘constexpr void std::vector<_Tp, > _Alloc>::_M_fill_append(size_type, const value_type&) [with _Tp = char; > _Alloc = std::allocator<char>]’ at > /mnt/gcc.bin/include/c++/17.0.0/bits/vector.tcc:776:36, > > > inlined from ‘constexpr void std::vector<_Tp, > _Alloc>::_M_fill_insert(iterator, size_type, const value_type&) [with _Tp = > char; _Alloc = std::allocator<char>]’ at > /mnt/gcc.bin/include/c++/17.0.0/bits/vector.tcc:668:20, > > > inlined from ‘constexpr std::vector<_Tp, _Alloc>::iterator > std::vector<_Tp, _Alloc>::insert(const_iterator, size_type, const > value_type&) [with _Tp = char; _Alloc = std::allocator<char>]’ at > /mnt/gcc.bin/include/c++/17.0.0/bits/stl_vector.h:1565:16, > > > inlined from ‘void foo()’ at > ./gcc/testsuite/g++.dg/torture/pr118521.C:12:11: > > > /mnt/gcc.bin/include/c++/17.0.0/bits/stl_uninitialized.h:577:39: > warning: ‘void* __builtin_memset(void*, int, long unsigned int)’ writing 2 > bytes into a region of size 0 overflows the destination > [-Wstringop-overflow=] > > > 577 | __builtin_memset(__dest, (unsigned > char)__x, __n); > > > | > ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > > > I think it's a victim of an existing (and very annoying) misdetection > of memory overwrites (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125187). > It's not directly related to my patch (which optimizes moving a range, not > filling it), but my patch changes the detection logic causing gcc to think > the region is of size 0 (where it should be 4). > > > > Yes, these middle-end warnings are a plague, but I don't see why your > > patch (which I pushed yesterday) changes the > > __uninitialized_fill_n_a() path which uses memset. Your patch only > > affects the uninitialized_copy() path which uses memcpy. > > The __uninitialized_fill_n_a function on line 776 is only used when > there's enough room for it: > > if (size_type(this->_M_impl._M_end_of_storage > - this->_M_impl._M_finish) >= __n) > { > _GLIBCXX_ASAN_ANNOTATE_GROW(__n); > this->_M_impl._M_finish = > std::__uninitialized_fill_n_a(this->_M_impl._M_finish, __n, __x, > _M_get_Tp_allocator()); > > But the poxy warning decides maybe there's some way to reach it where > (end_of_storage - finish) == 0. > > As Avi said, it's likely that the else branch for the condition above > got simplified by the patch, which allowed GCC to make better (and > then eventually, much worse) analysis for the call above. > > > How to proceed? I suggest to file a bug and mark the failure as XFAIL. > > > > > > > > > > > > > > > > > > I enhanced the test code to be a full program and verified it works > with asan. > > > > > > I'm not sure how to proceed. I don't want to patch pr118521.C to > disable -Wstringop-overflow, since that's what it's testing. > > > > > > Copying Richard, the original author of the test > (a2755339c6c9832467c573d956e91565943ecdc1). > > > > > >> > > >> > > >>> > > >>> > > >>> Used configuration : > > >>> *CI config* tcwg_gcc_check aarch64-linux-gnu > > >>> *configure and test flags:* none, autodetected on > aarch64-unknown-linux-gnu--disable-multilib --enable-fix-cortex-a53-835769 > --enable-fix-cortex-a53-843419 --with-arch=armv8-a > > >>> > > >>> We track this bug report under > https://linaro.atlassian.net/browse/GNU-1906. Please let us know if you > have a fix. > > >>> > > >>> If you have any questions regarding this report, please ask on > [email protected] mailing list. > > >>> > > >>> > -----------------8<--------------------------8<--------------------------8<-------------------------- > > >>> > > >>> The information below contains the details of the failures, and the > ways to reproduce a debug environment: > > >>> > > >>> You can find the failure logs in *.log.1.xz files in > > >>> * > http://54.172.246.49:9090/jobs/tcwg_gcc_check--master-aarch64-build/builds/10197/archive/artifacts/00-sumfiles/ > > >>> The full lists of regressions and improvements as well as configure > and make commands are in > > >>> * > http://54.172.246.49:9090/jobs/tcwg_gcc_check--master-aarch64-build/builds/10197/archive/artifacts/notify/ > > >>> The list of [ignored] baseline and flaky failures are in > > >>> * > http://54.172.246.49:9090/jobs/tcwg_gcc_check--master-aarch64-build/builds/10197/archive/artifacts/sumfiles/xfails.xfail > > >>> > > >>> Current build : > http://54.172.246.49:9090/jobs/tcwg_gcc_check--master-aarch64-build/builds/10197/archive/artifacts/ > > >>> Reference build : > http://54.172.246.49:9090/jobs/tcwg_gcc_check--master-aarch64-build/builds/10196/archive/artifacts/ > > >>> > > >>> Instruction to reproduce the build : > https://gitlab.com/LinaroLtd/tcwg/ci/interesting-commits/-/raw/master/gcc/sha1/79e29562907b454cdb867195b34cf63156d2d0cc/tcwg_gcc_check/master-aarch64/reproduction_instructions.txt > > >>> > > >>> Full commit : See in git+ssh://[email protected]/git/gcc.git >
