[clang] [clang] constexpr built-in elementwise popcount function. (PR #117473)

[Mariya Podchishchaeva via cfe-commits]

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@@ -797,3 +797,21 @@ static_assert(__builtin_reduce_xor((vector4int){(int)0x11111111, (int)0x22222222
 static_assert(__builtin_reduce_xor((vector4long){(long long)0x1111111111111111L, (long long)0x2222222222222222L, (long long)0x4444444444444444L, (long long)0x8888888888888888L}) == (long long)0xFFFFFFFFFFFFFFFFL);
 static_assert(__builtin_reduce_xor((vector4uint){0x11111111U, 0x22222222U, 0x44444444U, 0x88888888U}) == 0xFFFFFFFFU);
 static_assert(__builtin_reduce_xor((vector4ulong){0x1111111111111111UL, 0x2222222222222222UL, 0x4444444444444444UL, 0x8888888888888888UL}) == 0xFFFFFFFFFFFFFFFFUL);
+
+static_assert(__builtin_reduce_add(__builtin_elementwise_popcount((vector4int){1, 2, 3, 4})) == 5);
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Fznamznon wrote:

Could you please also add a test checking vector result but without using `__builtin_reduce_add` ?

https://github.com/llvm/llvm-project/pull/117473