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Read the processor once and take FMA into the AVX2 check

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/arch:AVX2 lets the compiler use FMA as well, so a processor that reports AVX2
without it would still stop the simulator. The comment on OSXSAVE no longer
says more than the bit does.
This commit is contained in:
maj00r
2026-11-03 20:42:28 +01:00
parent 16d665156c
commit 32d7417c22
1 changed files with 6 additions and 5 deletions
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11
StarterNG/Infrastructure/CpuFeatures.cs
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@@ -11,7 +11,7 @@ public static class CpuFeatures
/// the published builds stop at the first AVX2 instruction on an older x86
/// processor. Other architectures cannot run them at all, which is not this.
/// </summary>
public static bool LacksAvx2 =>
public static bool LacksAvx2 { get; } =
RuntimeInformation.ProcessArchitecture is Architecture.X64 or Architecture.X86 && !HasAvx2();
/// <summary>
@@ -23,10 +23,11 @@ public static class CpuFeatures
{
if (!X86Base.IsSupported || X86Base.CpuId(0, 0).Eax < 7)
return false;
// Leaf 1 ECX: bit 27 the system saves the extended registers (OSXSAVE), bit 28 AVX.
// Leaf 7 EBX: bit 5 AVX2.
const int osxsaveAndAvx = (1 << 27) | (1 << 28);
return (X86Base.CpuId(1, 0).Ecx & osxsaveAndAvx) == osxsaveAndAvx &&
// Leaf 1 ECX: bit 12 FMA, which /arch:AVX2 lets the compiler use too; bit 27 the
// system has turned XSAVE on (whether it saves the AVX registers is in XCR0,
// which .NET cannot read); bit 28 AVX. Leaf 7 EBX: bit 5 AVX2.
const int leaf1 = (1 << 12) | (1 << 27) | (1 << 28);
return (X86Base.CpuId(1, 0).Ecx & leaf1) == leaf1 &&
(X86Base.CpuId(7, 0).Ebx & (1 << 5)) != 0;
}
}