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. > > 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
