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adesitter opened this issue May 9, 2025 · 2 comments · May be fixed by #139430
Open

clang-tidy "cppcoreguidelines-pro-bounds-pointer-arithmetic" false negative #139241

adesitter opened this issue May 9, 2025 · 2 comments · May be fixed by #139430
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clang-tidy false-negative

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@adesitter
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adesitter commented May 9, 2025 •
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❯ clang-tidy --version
LLVM (http://llvm.org/):
LLVM version 20.1.2
Optimized build.

❯ cat g.cpp

#include <span>

auto g1(std::span<int> s, std::size_t i) {
    // pointer arithmetic **not** detected
    return *(s.data() + i);
}

auto g2(std::span<int> s, std::size_t i) {
    auto p = s.data();
    // pointer arithmetic detected
    return *(p + i);
}

❯ clang-tidy "--checks=-*,cppcoreguidelines-pro-bounds-pointer-arithmetic" -quiet g.cpp -- -std=c++20 --gcc-toolchain=/usr/local/gcc-15

4 warnings generated.
.../g.cpp:11:16: warning: do not use pointer arithmetic [cppcoreguidelines-pro-bounds-pointer-arithmetic]
   11 |     return *(p + i);
      |                ^

The usage of pointer arithmetic in function g1 is not detected.
@llvmbot
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llvmbot commented May 9, 2025

@llvm/issue-subscribers-clang-tidy

Author: Arnaud Desitter (adesitter)

❯ clang-tidy --version LLVM (http://llvm.org/): LLVM version 20.1.2 Optimized build.

❯ cat g.cpp
#include <span>

auto g1(std::span<int> s, std::size_t i) {
// pointer arithmetic not detected
return *(s.data() + i);
}

auto g2(std::span<int> s, std::size_t i) {
auto p = s.data();
// pointer arithmetic detected
return *(p + i);
}

❯ clang-tidy "--checks=-*,cppcoreguidelines-pro-bounds-pointer-arithmetic" -quiet g.cpp -- -std=c++20 --gcc-toolchain=/usr/local/gcc-15
4 warnings generated.
.../g.cpp:11:16: warning: do not use pointer arithmetic [cppcoreguidelines-pro-bounds-pointer-arithmetic]
11 | return *(p + i);
| ^

@adesitter
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For comparison:

❯ clang++ -std=c++20 -c g.cpp --gcc-toolchain=/usr/local/gcc-15 -Wunsafe-buffer-usage

g.cpp:5:16: warning: unsafe pointer arithmetic [-Wunsafe-buffer-usage]
    5 |     return *(s.data() + i);
      |              ~~^~~~~~
g.cpp:5:16: note: pass -fsafe-buffer-usage-suggestions to receive code hardening suggestions
g.cpp:11:14: warning: unsafe pointer arithmetic [-Wunsafe-buffer-usage]
   11 |     return *(p + i);
      |              ^
g.cpp:11:14: note: pass -fsafe-buffer-usage-suggestions to receive code hardening suggestions
2 warnings generated.

@vbvictor vbvictor linked a pull request May 11, 2025 that will close this issue
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@adesitter @llvmbot