From 3d0d65ead28685c2ab60718bb24b72f11a1dedef Mon Sep 17 00:00:00 2001
From: Marco Barbone <mbarbone@flatironinstitute.org>
Date: Tue, 10 Nov 2026 13:14:00 -0500
Subject: [PATCH] Fix spurious double-register instantiation in emulated
 batch_bool value ctors

The unconstrained kernel::set dispatch in emulated batch_bool value ctors instantiated an unrelated batch<double, emulated<96>> register. Emulated array registers are now filled directly (is_emulated_arch<A>), so no foreign register type is instantiated.

Assisted-by: Qwen3.8-27B-FP8
---
 include/xsimd/arch/xsimd_emulated.hpp |  3 ++-
 include/xsimd/types/xsimd_batch.hpp   |  5 +++--
 test/test_batch_bool.cpp              | 16 ++++++++++++++++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/xsimd/arch/xsimd_emulated.hpp b/include/xsimd/arch/xsimd_emulated.hpp
index e2cd04c91..2eb29c425 100644
--- a/include/xsimd/arch/xsimd_emulated.hpp
+++ b/include/xsimd/arch/xsimd_emulated.hpp
@@ -697,7 +697,8 @@ namespace xsimd
             return { typename batch<T, emulated<N>>::register_type { static_cast<T>(values)... } };
         }
 
-        template <class A, class T, size_t N, class... Values>
+        // no A parameter: callers pass no explicit template argument, so deduction stays constrained
+        template <class T, size_t N, class... Values>
         XSIMD_INLINE batch_bool<T, emulated<N>> set(batch_bool<T, emulated<N>> const&, requires_arch<emulated<N>>, Values... values) noexcept
         {
             static_assert(sizeof...(Values) == batch<T, emulated<N>>::size, "consistent init");
diff --git a/include/xsimd/types/xsimd_batch.hpp b/include/xsimd/types/xsimd_batch.hpp
index 448928f02..7de029d71 100644
--- a/include/xsimd/types/xsimd_batch.hpp
+++ b/include/xsimd/types/xsimd_batch.hpp
@@ -1215,7 +1215,7 @@ namespace xsimd
     template <class T, class A>
     template <class... Ts>
     XSIMD_INLINE batch_bool<T, A>::batch_bool(bool val0, bool val1, Ts... vals) noexcept
-        : batch_bool(kernel::set<A>(batch_bool {}, A {}, val0, val1, static_cast<bool>(vals)...))
+        : batch_bool(make_register(std::index_sequence<> {}, val0, val1, static_cast<bool>(vals)...))
     {
         static_assert(sizeof...(Ts) + 2 == size, "The constructor requires as many arguments as batch elements.");
     }
@@ -1387,7 +1387,8 @@ namespace xsimd
     template <class... V>
     XSIMD_INLINE auto batch_bool<T, A>::make_register(std::index_sequence<>, V... v) noexcept -> register_type
     {
-        return kernel::set<A>(batch_bool<T, A>(), A {}, v...).data;
+        // no explicit template argument here: kernel::set<A> would instantiate unrelated register types
+        return kernel::set(batch_bool<T, A>(), A {}, v...).data;
     }
 
     /*******************************
diff --git a/test/test_batch_bool.cpp b/test/test_batch_bool.cpp
index 8f7b941fe..48e8d79d2 100644
--- a/test/test_batch_bool.cpp
+++ b/test/test_batch_bool.cpp
@@ -1002,4 +1002,20 @@ TEST_CASE_TEMPLATE("batch_bool mask hygiene", B, BATCH_TYPES)
     }
 }
 
+#if XSIMD_WITH_EMULATED
+TEST_CASE("emulated batch_bool construction")
+{
+    using M = xsimd::batch_bool<float, xsimd::emulated<96>>;
+
+    M const all_true(true);
+    CHECK(all_true.get(0));
+    CHECK(all_true.get(M::size - 1));
+
+    M const lanes(true, false, true);
+    CHECK(lanes.get(0));
+    CHECK_FALSE(lanes.get(1));
+    CHECK(lanes.get(2));
+}
+#endif
+
 #endif