https://gcc.gnu.org/g:e77f314ccd422ffa05c6c06837e2cb94c25f2bba
commit r14-10331-ge77f314ccd422ffa05c6c06837e2cb94c25f2bba
Author: Matthias Kretz <m.kr...@gsi.de>
Date: Fri Jun 14 15:11:25 2024 +0200
libstdc++: Fix find_last_set(simd_mask) to ignore padding bits
With the change to the AVX512 find_last_set implementation, the change
to AVX512 operator!= is unnecessary. However, the latter was not
producing optimal code and unnecessarily set the padding bits. In
theory, the compiler could determine that with the new !=
implementation, the bit operation for clearing the padding bits is a
no-op and can be elided.
Signed-off-by: Matthias Kretz <m.kr...@gsi.de>
libstdc++-v3/ChangeLog:
PR libstdc++/115454
* include/experimental/bits/simd_x86.h (_S_not_equal_to): Use
neq comparison instead of bitwise negation after eq.
(_S_find_last_set): Clear unused high bits before computing
bit_width.
* testsuite/experimental/simd/pr115454_find_last_set.cc: New
test.
(cherry picked from commit 1340ddea0158de3f49aeb75b4013e5fc313ff6f4)
Diff:
---
libstdc++-v3/include/experimental/bits/simd_x86.h | 26 ++++++------
.../experimental/simd/pr115454_find_last_set.cc | 49 ++++++++++++++++++++++
2 files changed, 62 insertions(+), 13 deletions(-)
diff --git a/libstdc++-v3/include/experimental/bits/simd_x86.h
b/libstdc++-v3/include/experimental/bits/simd_x86.h
index 517c4b4a5bec..8a23aa2082b0 100644
--- a/libstdc++-v3/include/experimental/bits/simd_x86.h
+++ b/libstdc++-v3/include/experimental/bits/simd_x86.h
@@ -2339,29 +2339,29 @@ template <typename _Abi, typename>
__assert_unreachable<_Tp>();
}
else if constexpr (sizeof(__xi) == 64 && sizeof(_Tp) == 8)
- return ~_mm512_mask_cmpeq_epi64_mask(__k1, __xi, __yi);
+ return _mm512_mask_cmpneq_epi64_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 64 && sizeof(_Tp) == 4)
- return ~_mm512_mask_cmpeq_epi32_mask(__k1, __xi, __yi);
+ return _mm512_mask_cmpneq_epi32_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 64 && sizeof(_Tp) == 2)
- return ~_mm512_mask_cmpeq_epi16_mask(__k1, __xi, __yi);
+ return _mm512_mask_cmpneq_epi16_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 64 && sizeof(_Tp) == 1)
- return ~_mm512_mask_cmpeq_epi8_mask(__k1, __xi, __yi);
+ return _mm512_mask_cmpneq_epi8_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 32 && sizeof(_Tp) == 8)
- return ~_mm256_mask_cmpeq_epi64_mask(__k1, __xi, __yi);
+ return _mm256_mask_cmpneq_epi64_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 32 && sizeof(_Tp) == 4)
- return ~_mm256_mask_cmpeq_epi32_mask(__k1, __xi, __yi);
+ return _mm256_mask_cmpneq_epi32_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 32 && sizeof(_Tp) == 2)
- return ~_mm256_mask_cmpeq_epi16_mask(__k1, __xi, __yi);
+ return _mm256_mask_cmpneq_epi16_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 32 && sizeof(_Tp) == 1)
- return ~_mm256_mask_cmpeq_epi8_mask(__k1, __xi, __yi);
+ return _mm256_mask_cmpneq_epi8_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 16 && sizeof(_Tp) == 8)
- return ~_mm_mask_cmpeq_epi64_mask(__k1, __xi, __yi);
+ return _mm_mask_cmpneq_epi64_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 16 && sizeof(_Tp) == 4)
- return ~_mm_mask_cmpeq_epi32_mask(__k1, __xi, __yi);
+ return _mm_mask_cmpneq_epi32_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 16 && sizeof(_Tp) == 2)
- return ~_mm_mask_cmpeq_epi16_mask(__k1, __xi, __yi);
+ return _mm_mask_cmpneq_epi16_mask(__k1, __xi, __yi);
else if constexpr (sizeof(__xi) == 16 && sizeof(_Tp) == 1)
- return ~_mm_mask_cmpeq_epi8_mask(__k1, __xi, __yi);
+ return _mm_mask_cmpneq_epi8_mask(__k1, __xi, __yi);
else
__assert_unreachable<_Tp>();
} // }}}
@@ -5292,7 +5292,7 @@ template <typename _Abi, typename>
_S_find_last_set(simd_mask<_Tp, _Abi> __k)
{
if constexpr (__is_avx512_abi<_Abi>())
- return std::__bit_width(__k._M_data._M_data) - 1;
+ return std::__bit_width(_Abi::_S_masked(__k._M_data)._M_data) - 1;
else
return _Base::_S_find_last_set(__k);
}
diff --git a/libstdc++-v3/testsuite/experimental/simd/pr115454_find_last_set.cc
b/libstdc++-v3/testsuite/experimental/simd/pr115454_find_last_set.cc
new file mode 100644
index 000000000000..b47f19d30674
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/simd/pr115454_find_last_set.cc
@@ -0,0 +1,49 @@
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target *-*-* } }
+// { dg-require-effective-target c++17 }
+// { dg-additional-options "-march=x86-64-v4" { target avx512f } }
+// { dg-require-cmath "" }
+
+#include <experimental/simd>
+
+namespace stdx = std::experimental;
+
+using T = std::uint64_t;
+
+template <typename U, int N>
+using V = stdx::simd<U, stdx::simd_abi::deduce_t<U, N>>;
+
+[[gnu::noinline, gnu::noipa]]
+int reduce(V<T, 4> x)
+{
+ static_assert(stdx::find_last_set(V<T, 4>([](unsigned i) { return i; }) !=
V<T, 4>(0)) == 3);
+ return stdx::find_last_set(x != -1);
+}
+
+[[gnu::noinline, gnu::noipa]]
+int reduce2()
+{
+ using M8 = typename V<short, 8>::mask_type;
+ using M4 = typename V<int, 4>::mask_type;
+ if constexpr (sizeof(M8) == sizeof(M4))
+ {
+ M4 k;
+ __builtin_memcpy(&__data(k), &__data(M8(true)), sizeof(M4));
+ return stdx::find_last_set(k);
+ }
+ return 3;
+}
+
+
+int main()
+{
+ const V<T, 4> x {};
+
+ const int r = reduce(x);
+ if (r != 3)
+ __builtin_abort();
+
+ const int r2 = reduce2();
+ if (r2 != 3)
+ __builtin_abort();
+}
