Work around GCC 12 false positive warning for string::insert #14265
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GCC 12's stricter -Wrestrict analysis detects potential overlapping memory regions in std::string::insert() when shifting characters within the same buffer. This triggers build failures on: - CentOS 7 (x86_64 and aarch64) with GCC 12.1.1 - Alpine 3.18 (PPC64le) with GCC 12.2.1 The issue occurs because insert(pos, str) must shift all characters from position pos to the end rightward to make room for the new content. This shifting copies from [pos, end) to [pos+len, end+len) within the same buffer - overlapping regions. The libstdc++ implementation uses memcpy (via char_traits::copy) for this operation, but memcpy has undefined behavior when source and destination overlap. push_back() does not have this problem because it only appends to the end of the string. No existing characters need to be moved, so there are no overlapping memory regions. Fix by building the output string incrementally using push_back() instead of modifying in-place with insert(). This also eliminates repeated character shifting, making it slightly more efficient.
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@mszeszko-meta has imported this pull request. If you are a Meta employee, you can view this in D91594561. |
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pdillinger
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Jan 27, 2026
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I see existing unit tests for this function, so 👍
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@mszeszko-meta merged this pull request in acfea34. |
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Work around a warning/linter false positive related to the use of
string::insert. The code in question is legal C++, but GCC 12'slibstdc++implementation ofstring::insertinternally usesmemcpy, which can trigger undefined behavior warnings when the source and destination overlap.