[PATCH] libstdc++: arm: convert vpadd_* operands to intrinsic types [PR122981]

[Jonathan Wakely]

On Sun, 12 Jul 2026 at 19:42 +0200, Torbjörn SVENSSON wrote:
>I hope this is the right fix for the issue.
>I've regtested for arm-none-eabi on top of r15-11320-g7909a9f85f30b6 and it applies cleanly on trunk.
>The new test is derived from libstdc++-v3/testsuite/experimental/simd/pr115454_find_last_set.cc.
>
>Ok for trunk, releases/gcc-16 and releases/gcc-15?

OK for trunk but for the backports I'd prefer to wait for Matthias to
confirm this is the correct fix.

>--
>
>When testing r15-10798-gae573c9d0e7f1c, I noticed that the
>experimental/simd/pr115454_find_last_set.cc was failing due to that the
>GNU vector type was used instead of the NEON intrinsic type.
>
>	PR libstdc++/122981
>
>libstdc++-v3/ChangeLog:
>
>	* include/experimental/bits/simd_neon.h: Convert AArch32 NEON
>	vpadd_* operands to intrinsic types.
>	* testsuite/experimental/simd/pr122981_find_last_set_neon.cc: New test.
>
>Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
>---
> .../include/experimental/bits/simd_neon.h     | 31 +++++++-----
> .../simd/pr122981_find_last_set_neon.cc       | 50 +++++++++++++++++++
> 2 files changed, 69 insertions(+), 12 deletions(-)
> create mode 100644 libstdc++-v3/testsuite/experimental/simd/pr122981_find_last_set_neon.cc
>
>diff --git a/libstdc++-v3/include/experimental/bits/simd_neon.h b/libstdc++-v3/include/experimental/bits/simd_neon.h
>index d3785db2bfd..23c205f3dc9 100644
>--- a/libstdc++-v3/include/experimental/bits/simd_neon.h
>+++ b/libstdc++-v3/include/experimental/bits/simd_neon.h
>@@ -297,9 +297,10 @@ struct _MaskImplNeonMixin
> 			  __zero))[0];
> #else
> 	      return __vector_bitcast<_UShort>(
>-		vpadd_s8(vpadd_s8(vpadd_s8(__lo64(__asint), __hi64(__asint)),
>-				  __zero),
>-			 __zero))[0];
>+		vpadd_s8(vpadd_s8(vpadd_s8(__to_intrin(__lo64(__asint)),
>+					    __to_intrin(__hi64(__asint))),
>+				  __to_intrin(__zero)),
>+			 __to_intrin(__zero)))[0];
> #endif
> 	    }
> 	  else if constexpr (sizeof(_Tp) == 2)
>@@ -313,9 +314,10 @@ struct _MaskImplNeonMixin
> #ifdef __aarch64__
> 	      return vaddvq_s16(__asint);
> #else
>-	      return vpadd_s16(
>-		vpadd_s16(vpadd_s16(__lo64(__asint), __hi64(__asint)), __zero),
>-		__zero)[0];
>+	      return vpadd_s16(vpadd_s16(vpadd_s16(__to_intrin(__lo64(__asint)),
>+						   __to_intrin(__hi64(__asint))),
>+					 __to_intrin(__zero)),
>+			       __to_intrin(__zero))[0];
> #endif
> 	    }
> 	  else if constexpr (sizeof(_Tp) == 4)
>@@ -329,8 +331,9 @@ struct _MaskImplNeonMixin
> #ifdef __aarch64__
> 	      return vaddvq_s32(__asint);
> #else
>-	      return vpadd_s32(vpadd_s32(__lo64(__asint), __hi64(__asint)),
>-			       __zero)[0];
>+	      return vpadd_s32(vpadd_s32(__to_intrin(__lo64(__asint)),
>+					 __to_intrin(__hi64(__asint))),
>+			       __to_intrin(__zero))[0];
> #endif
> 	    }
> 	  else if constexpr (sizeof(_Tp) == 8)
>@@ -353,8 +356,10 @@ struct _MaskImplNeonMixin
> #ifdef __aarch64__
> 	      return vaddv_s8(__asint);
> #else
>-	      return vpadd_s8(vpadd_s8(vpadd_s8(__asint, __zero), __zero),
>-			      __zero)[0];
>+	      return vpadd_s8(vpadd_s8(vpadd_s8(__to_intrin(__asint),
>+						__to_intrin(__zero)),
>+				       __to_intrin(__zero)),
>+			      __to_intrin(__zero))[0];
> #endif
> 	    }
> 	  else if constexpr (sizeof(_Tp) == 2)
>@@ -368,7 +373,9 @@ struct _MaskImplNeonMixin
> #ifdef __aarch64__
> 	      return vaddv_s16(__asint);
> #else
>-	      return vpadd_s16(vpadd_s16(__asint, __zero), __zero)[0];
>+	      return vpadd_s16(vpadd_s16(__to_intrin(__asint),
>+					 __to_intrin(__zero)),
>+			       __to_intrin(__zero))[0];
> #endif
> 	    }
> 	  else if constexpr (sizeof(_Tp) == 4)
>@@ -377,7 +384,7 @@ struct _MaskImplNeonMixin
> #ifdef __aarch64__
> 	      return vaddv_s32(__asint);
> #else
>-	      return vpadd_s32(__asint, __zero)[0];
>+	      return vpadd_s32(__to_intrin(__asint), __to_intrin(__zero))[0];
> #endif
> 	    }
> 	  else
>diff --git a/libstdc++-v3/testsuite/experimental/simd/pr122981_find_last_set_neon.cc b/libstdc++-v3/testsuite/experimental/simd/pr122981_find_last_set_neon.cc
>new file mode 100644
>index 00000000000..f7f79166ae6
>--- /dev/null
>+++ b/libstdc++-v3/testsuite/experimental/simd/pr122981_find_last_set_neon.cc
>@@ -0,0 +1,50 @@
>+// { dg-options "-std=gnu++17" }
>+// { dg-do compile { target c++17 } }
>+// { dg-require-effective-target arm_neon_ok }
>+// { dg-add-options arm_neon }
>+// { dg-require-cmath "" }
>+
>+#include <experimental/simd>
>+
>+namespace stdx = std::experimental;
>+
>+template <typename U, int N>
>+using V = stdx::simd<U, stdx::simd_abi::deduce_t<U, N>>;
>+
>+template <typename U, int N>
>+[[gnu::noinline, gnu::noipa]]
>+int reduce(typename V<U, N>::mask_type x)
>+{
>+  using M = typename V<U, N>::mask_type;
>+  static_assert(stdx::find_last_set(M(true)) == N - 1);
>+  return stdx::find_last_set(x);
>+}
>+
>+int main()
>+{
>+  // 16 bytes: 16 int8_t lanes, 8 int16_t lanes, 4 int32_t lanes.
>+  const int r_int8_16 = reduce<std::int8_t, 16>(typename V<std::int8_t, 16>::mask_type(true));
>+  if (r_int8_16 != 15)
>+    __builtin_abort();
>+
>+  const int r_int16_8 = reduce<std::int16_t, 8>(typename V<std::int16_t, 8>::mask_type(true));
>+  if (r_int16_8 != 7)
>+    __builtin_abort();
>+
>+  const int r_int32_4 = reduce<std::int32_t, 4>(typename V<std::int32_t, 4>::mask_type(true));
>+  if (r_int32_4 != 3)
>+    __builtin_abort();
>+
>+  // 8 bytes: 8 int8_t lanes, 4 int16_t lanes, 2 int32_t lanes.
>+  const int r_int8_8 = reduce<std::int8_t, 8>(typename V<std::int8_t, 8>::mask_type(true));
>+  if (r_int8_8 != 7)
>+    __builtin_abort();
>+
>+  const int r_int16_4 = reduce<std::int16_t, 4>(typename V<std::int16_t, 4>::mask_type(true));
>+  if (r_int16_4 != 3)
>+    __builtin_abort();
>+
>+  const int r_int32_2 = reduce<std::int32_t, 2>(typename V<std::int32_t, 2>::mask_type(true));
>+  if (r_int32_2 != 1)
>+    __builtin_abort();
>+}
>-- 
>2.43.0
>
>