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From: "nekotekina at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/103932] New: x86: strange unoptimized code generated (multiple negations of _mm_testz_si128 result) Date: Thu, 06 Jan 2022 19:11:03 +0000 [thread overview] Message-ID: <bug-103932-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103932 Bug ID: 103932 Summary: x86: strange unoptimized code generated (multiple negations of _mm_testz_si128 result) Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: nekotekina at gmail dot com Target Milestone: --- GCC generates seemingly unoptimized sequence of instructions in certain cases (can't tell exactly what triggers it, example code is below): xor eax, eax vptest xmm0, xmm0 sete al test eax, eax sete al movzx eax, al This should be something like this: xor eax, eax vptest xmm0, xmm0 setne al https://godbolt.org/z/sTaG65Ksc Code (-O3 -std=c++20 -march=skylake): #include <emmintrin.h> #include <immintrin.h> #include <bit> #include <cstdint> template <typename T> concept Vector128 = (sizeof(T) == 16); using u64 = std::uint64_t; using u32 = std::uint32_t; union alignas(16) v128 { u64 _u64[2]; v128() = default; constexpr v128(const v128&) noexcept = default; template <Vector128 T> constexpr v128(const T& rhs) noexcept : v128(std::bit_cast<v128>(rhs)) { } constexpr v128& operator=(const v128&) noexcept = default; template <Vector128 T> constexpr operator T() const noexcept { return std::bit_cast<T>(*this); } }; // Test if vector is zero inline bool gv_testz(const v128& arg) { #if defined(__SSE4_1__) return _mm_testz_si128(arg, arg); #else return !(arg._u64[0] | arg._u64[1]); #endif } struct alignas(16) context_t { v128 vec[32]; v128 sat; }; void test1(context_t& ctx, u32 n) { const u64 bit = !gv_testz(ctx.sat); v128 r; r._u64[0] = 0; r._u64[1] = bit; ctx.vec[n] = r; } void test2(context_t& ctx, u32 n) { ctx.vec[n]._u64[1] = !gv_testz(ctx.sat); }
next reply other threads:[~2022-01-06 19:11 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-01-06 19:11 nekotekina at gmail dot com [this message] 2022-01-06 21:23 ` [Bug target/103932] " pinskia at gcc dot gnu.org 2022-01-06 21:25 ` pinskia at gcc dot gnu.org
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