https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120358
--- Comment #17 from Holger Hoffstätte <hol...@applied-asynchrony.com> --- Created attachment 61755 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61755&action=edit Readable reproducer for debugging (In reply to rguent...@suse.de from comment #16) > Does -fno-lifetime-dse help? It does not (in any example). I also get the impression that small.cxx now demonstrates a different problem than before, but that might just be fallout from what I'm about to show; this hole goes deeper. With my "readable.cpp" attachment (still needs Qt): holger>gdb a.out (gdb) b dump Breakpoint 1 at 0x148f: dump. (2 locations) (gdb) r Starting program: /mnt/tux/holger/Projects/qt6-gcc15/a.out [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib64/libthread_db.so.1". Breakpoint 1.1, dump<QStringTokenizer<QStringView, QChar> > (tok=<synthetic pointer>...) at readable.cpp:8 8 for (auto &x : tok) { (gdb) p tok.m_haystack $1 = {m_size = 19, m_data = 0x55555556f650 u"a.ab.abc.abcd.abcde"} --> looks fine (gdb) c Continuing. 1 2 3 4 5 --> as expected Breakpoint 1.2, dump<QStringTokenizer<QString, QChar> > (tok=...) at readable.cpp:8 8 for (auto &x : tok) { (gdb) p tok.m_haystack $2 = {m_size = 93824992343616, m_data = 0x55555556f650 u"a.ab.abc.abcd.abcde"} --> m_size is obviously bogus (gdb) c Continuing. 1 2 3 4 5 18446744073709551615 The interesting difference here is that the tokenizer "pins" moved-into haystacks and that's when things go wrong. Unpinned (good): Breakpoint 1.1, dump<QStringTokenizer<QStringView, QChar> > (tok=<synthetic pointer>...) at readable.cpp:8 8 for (auto &x : tok) { (gdb) p tok $1 = (QStringTokenizer<QStringView, QChar> &) <synthetic pointer>: {<QtPrivate::Tok::HaystackPinning<QStringView>> = {<QtPrivate::Tok::Pinning<QStringView, false>> = {<No data fields>}, <No data fields>}, <QtPrivate::Tok::NeedlePinning<QChar>> = {<QtPrivate::Tok::Pinning<QChar, false>> = {<No data fields>}, <No data fields>}, <QStringTokenizerBase<QStringView, QChar>> = {<QStringTokenizerBaseBase> = { m_sb = {<QtPrivate::QFlagsStorageHelper<Qt::SplitBehaviorFlags, 4>> = {<QtPrivate::QFlagsStorage<Qt::SplitBehaviorFlags>> = {static IntegerSize = 4, i = <optimized out>}, <No data fields>}, <No data fields>}, m_cs = <optimized out>}, m_haystack = {m_size = 19, m_data = 0x55555556f650 u"a.ab.abc.abcd.abcde"}, m_needle = {ucs = <optimized out>}}, <No data fields>} (gdb) c Continuing. 1 2 3 4 5 Pinned (wrong): Breakpoint 1.2, dump<QStringTokenizer<QString, QChar> > (tok=...) at readable.cpp:8 8 for (auto &x : tok) { (gdb) p tok $2 = (QStringTokenizer<QString, QChar> &) @0x7fffffffde20: {<QtPrivate::Tok::HaystackPinning<QString>> = {<QtPrivate::Tok::Pinning<QString, true>> = {m_string = {d = { d = 0xffffffffffff002e, ptr = 0x55555556f650 u"a.ab.abc.abcd.abcde", size = 19}}}, <No data fields>}, <QtPrivate::Tok::NeedlePinning<QChar>> = {<QtPrivate::Tok::Pinning<QChar, false>> = {<No data fields>}, <No data fields>}, <QStringTokenizerBase<QStringView, QChar>> = {<QStringTokenizerBaseBase> = { m_sb = {<QtPrivate::QFlagsStorageHelper<Qt::SplitBehaviorFlags, 4>> = {<QtPrivate::QFlagsStorage<Qt::SplitBehaviorFlags>> = {static IntegerSize = 4, i = 1}, <No data fields>}, <No data fields>}, m_cs = Qt::CaseSensitive}, m_haystack = {m_size = 93824992343616, m_data = 0x55555556f650 u"a.ab.abc.abcd.abcde"}, m_needle = {ucs = 46 u'.'}}, <No data fields>} (gdb) c Continuing. 1 2 3 4 5 18446744073709551615 We can see that Pinning<QString, true> has size=19 (correct), but m_haystack has m_size = 93824992343616 (wrong).
