[libc][NFC] Selectively disable GCC warnings

[gchatelet]

No description provided.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Guillaume Chatelet (gchatelet)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/78462.diff

2 Files Affected:

• (modified) libc/src/string/memory_utils/op_x86.h (+7)
• (modified) libc/src/string/memory_utils/utils.h (+3-1)

diff --git a/libc/src/string/memory_utils/op_x86.h b/libc/src/string/memory_utils/op_x86.h
index 6ae9583627bd6d3..f7897a7f9fd7205 100644
--- a/libc/src/string/memory_utils/op_x86.h
+++ b/libc/src/string/memory_utils/op_x86.h
@@ -25,6 +25,11 @@
 #include <immintrin.h>
 #endif
 
+// Disable GCC complaining about missing attributes when using SIMD types in
+// template specializations.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wignored-attributes"
+
 // Define fake functions to prevent the compiler from failing on undefined
 // functions in case the CPU extension is not present.
 #if !defined(__AVX512BW__) && (defined(_MSC_VER) || defined(__SCE__))
@@ -306,6 +311,8 @@ LIBC_INLINE MemcmpReturnType cmp_neq<__m512i>(CPtr p1, CPtr p2, size_t offset) {
 
 } // namespace LIBC_NAMESPACE::generic
 
+#pragma GCC diagnostic pop
+
 #endif // LIBC_TARGET_ARCH_IS_X86_64
 
 #endif // LLVM_LIBC_SRC_STRING_MEMORY_UTILS_OP_X86_H
diff --git a/libc/src/string/memory_utils/utils.h b/libc/src/string/memory_utils/utils.h
index 5cd716e033d6a4c..543d45b7c4e33e3 100644
--- a/libc/src/string/memory_utils/utils.h
+++ b/libc/src/string/memory_utils/utils.h
@@ -89,9 +89,11 @@ LIBC_INLINE void memcpy_inline(void *__restrict dst,
   // In memory functions `memcpy_inline` is instantiated several times with
   // different value of the Size parameter. This doesn't play well with GCC's
   // Value Range Analysis that wrongly detects out of bounds accesses. We
-  // disable the 'array-bounds' warning for the purpose of this function.
+  // disable these warnings for the purpose of this function.
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Warray-bounds"
+#pragma GCC diagnostic ignored "-Wstringop-overread"
+#pragma GCC diagnostic ignored "-Wstringop-overflow"
   for (size_t i = 0; i < Size; ++i)
     static_cast<char *>(dst)[i] = static_cast<const char *>(src)[i];
 #pragma GCC diagnostic pop

[nickdesaulniers]

Which attributes is it complaining about? Mind adding that to the commit message?

[gchatelet]

It doesn't say which ones ☹

[17/29] Building CXX object projects/libc/test/src/__support/FPUtil/CMakeFiles/libc.test.src.__support.FPUtil.fpbits_test.__unit__.__build__.dir/fpbits_test.cpp.o
In file included from /redacted/gchatelet/git/llvm-project/libc/src/string/memory_utils/x86_64/inline_memcpy.h:15,
                 from /redacted/gchatelet/git/llvm-project/libc/src/string/memory_utils/inline_memcpy.h:22,
                 from /redacted/gchatelet/git/llvm-project/libc/src/__support/CPP/string.h:14,
                 from /redacted/gchatelet/git/llvm-project/libc/src/__support/FPUtil/fpbits_str.h:12,
                 from /redacted/gchatelet/git/llvm-project/libc/test/src/__support/FPUtil/fpbits_test.cpp:10:
/redacted/gchatelet/git/llvm-project/libc/src/string/memory_utils/op_x86.h:122:37: warning: ignoring attributes on template argument ‘__m128i’ [-Wignored-attributes]
  122 | template <> struct is_vector<__m128i> : cpp::true_type {};
      |                                     ^
/redacted/gchatelet/git/llvm-project/libc/src/string/memory_utils/op_x86.h:123:44: warning: ignoring attributes on template argument ‘__m128i’ [-Wignored-attributes]
  123 | template <> struct cmp_is_expensive<__m128i> : cpp::true_type {};
      |                                            ^
/redacted/gchatelet/git/llvm-project/libc/src/string/memory_utils/op_x86.h:162:37: warning: ignoring attributes on template argument ‘__m256i’ [-Wignored-attributes]
  162 | template <> struct is_vector<__m256i> : cpp::true_type {};
      |                                     ^
/redacted/gchatelet/git/llvm-project/libc/src/string/memory_utils/op_x86.h:163:44: warning: ignoring attributes on template argument ‘__m256i’ [-Wignored-attributes]
  163 | template <> struct cmp_is_expensive<__m256i> : cpp::true_type {};
      |                                            ^

[gchatelet]

Looking at __m256i definition

/usr/lib/llvm-16/lib/clang/16/include/avxintrin.h:typedef long long __m256i __attribute__((__vector_size__(32), __aligned__(32)));

[gchatelet]

I tried a better explanation, let me know what you think.

[nickdesaulniers]

ah, yeah https://stackoverflow.com/questions/41676311/implication-of-gcc-warning-ignoring-attributes-on-template-argument-wignored has more context. I was just looking at /usr/lib/gcc/x86_64-linux-gnu/13/include/avxintrin.h myself.

Do you mind mimimizing the region of code for which the pragma is disabled? I think the initial push+disable could be "sunk" lower in the header. That might help avoid false negatives that result from disabling the diagnostics.

[gchatelet]

Sure thing. Done!

[nickdesaulniers]

nice work, thank you!