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| author | Jonathan Wakely <jwakely@redhat.com> | 2023-03-28 10:50:40 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2023-03-28 21:12:18 +0100 |
| commit | bf78b43873b0b7e8f9a430df38749b8b61f9c9b8 (patch) | |
| tree | ff6f661fe5972bb61b27e118123eb5eeeb4808e0 | |
| parent | cf19ef9eca82b01dd0a3a0a8e4c8bcec236eb2d9 (diff) | |
| download | gcc-bf78b43873b0b7e8f9a430df38749b8b61f9c9b8.zip gcc-bf78b43873b0b7e8f9a430df38749b8b61f9c9b8.tar.gz gcc-bf78b43873b0b7e8f9a430df38749b8b61f9c9b8.tar.bz2 | |
libstdc++: Tell GCC what basic_string::_M_is_local() means [PR109299]
This avoids a bogus warning about overflowing a buffer, because GCC
can't tell that we don't copy into the buffer unless it fits. By adding
a __builtin_unreachable() hint we inform the compiler about the
invariant that the buffer is only used when it's big enough.
This can also improve codegen, by eliminating dead code that GCC
couldn't tell was unreachable.
libstdc++-v3/ChangeLog:
PR libstdc++/109299
* include/bits/basic_string.h (basic_string::_M_is_local()): Add
hint for compiler that local strings fit in the local buffer.
| -rw-r--r-- | libstdc++-v3/include/bits/basic_string.h | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h index 1b8ebca..5d040e2 100644 --- a/libstdc++-v3/include/bits/basic_string.h +++ b/libstdc++-v3/include/bits/basic_string.h @@ -271,7 +271,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 _GLIBCXX20_CONSTEXPR bool _M_is_local() const - { return _M_data() == _M_local_data(); } + { + if (_M_data() == _M_local_data()) + { + if (_M_string_length > _S_local_capacity) + __builtin_unreachable(); + return true; + } + return false; + } // Create & Destroy _GLIBCXX20_CONSTEXPR |