84b05bd20a
Depends on hardware support, detected and runtime and controllable via a64_extension_mask bit 1.
93 lines
3.1 KiB
C++
93 lines
3.1 KiB
C++
/**
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******************************************************************************
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* Xenia : Xbox 360 Emulator Research Project *
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******************************************************************************
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* Copyright 2026 Ben Vanik. All rights reserved. *
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* Released under the BSD license - see LICENSE in the root for more details. *
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******************************************************************************
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*/
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#include <cfenv>
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#include <cmath>
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#include <cstring>
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#include "xenia/base/cvar.h"
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#include "xenia/base/platform.h"
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#define XBYAK_NO_OP_NAMES
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#include "third_party/xbyak_aarch64/xbyak_aarch64/xbyak_aarch64.h"
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#include "third_party/xbyak_aarch64/xbyak_aarch64/xbyak_aarch64_util.h"
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DEFINE_int64(a64_extension_mask, -1LL,
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"Allow the detection and utilization of specific instruction set "
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"features.\n"
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" 0 = armv8.0\n"
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" 1 = Large System Extensions(LSE) atomic operations\n"
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" 2 = FPCR.FZ flushes denormal inputs (skip software flush)\n"
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" -1 = Detect and utilize all possible processor features\n",
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"a64");
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namespace xe {
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namespace arm64 {
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static uint64_t g_feature_flags = 0U;
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static bool g_did_initialize_feature_flags = false;
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uint64_t GetFeatureFlags() {
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if (!g_did_initialize_feature_flags) {
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InitFeatureFlags();
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}
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return g_feature_flags;
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}
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XE_COLD
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XE_NOINLINE
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void InitFeatureFlags() {
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uint64_t feature_flags_ = 0U;
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{
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Xbyak_aarch64::util::Cpu cpu_;
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#define TEST_EMIT_FEATURE(emit, ext) \
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if ((cvars::a64_extension_mask & emit) == emit) { \
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feature_flags_ |= (cpu_.has(ext) ? emit : 0); \
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}
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TEST_EMIT_FEATURE(kA64EmitLSE,
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Xbyak_aarch64::util::XBYAK_AARCH64_HWCAP_ATOMIC);
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#undef TEST_EMIT_FEATURE
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}
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// Detect whether FPCR.FZ flushes denormal float32 inputs to zero.
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// The ARM spec says input flushing is implementation-defined.
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// Modern cores (Cortex-A76+, Apple M1+) flush inputs; older ones may not.
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if ((cvars::a64_extension_mask & kA64FZFlushesInputs) ==
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kA64FZFlushesInputs) {
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// Build a denormal float32: smallest positive denormal = 0x00000001.
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uint32_t denorm_bits = 1;
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float denorm;
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std::memcpy(&denorm, &denorm_bits, 4);
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// Save FPCR, enable FZ, add two denormals, check result.
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uint64_t saved_fpcr;
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#if XE_COMPILER_MSVC
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saved_fpcr = _ReadStatusReg(ARM64_FPCR);
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_WriteStatusReg(ARM64_FPCR, saved_fpcr | (1ULL << 24));
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#else
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asm volatile("mrs %0, fpcr" : "=r"(saved_fpcr));
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uint64_t fz_fpcr = saved_fpcr | (1ULL << 24);
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asm volatile("msr fpcr, %0" ::"r"(fz_fpcr));
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#endif
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volatile float a = denorm;
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volatile float b = denorm;
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volatile float result = a + b;
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#if XE_COMPILER_MSVC
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_WriteStatusReg(ARM64_FPCR, saved_fpcr);
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#else
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asm volatile("msr fpcr, %0" ::"r"(saved_fpcr));
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#endif
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if (result == 0.0f) {
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feature_flags_ |= kA64FZFlushesInputs;
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}
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}
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g_feature_flags = feature_flags_;
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g_did_initialize_feature_flags = true;
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}
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} // namespace arm64
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} // namespace xe
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