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Comment by whaleofatw2022 | Hacker News Reader

whaleofatw2022

One exception that does come to mind, is .Net Framework on x86. AFAIR that didn't use SSE or SSE2. (In x64 mode it did however, since those were part of the baseline for x64)

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Strange, because .NET was specifically designed to be a JITted environment and taking advantage of SSE2 when available would ordinarily be an advantage of a JIT. But sure enough, .NET 4.0 x86 still uses x87 instructions for math. It's not even good x87, this is surprisingly bad:

  01b2086a 8975e4          mov     dword ptr [ebp-1Ch],esi
  01b2086d db45e4          fild    dword ptr [ebp-1Ch]
  01b20870 d95de4          fstp    dword ptr [ebp-1Ch]
  01b20873 d945e4          fld     dword ptr [ebp-1Ch]
  01b20876 d80dcc08b201    fmul    dword ptr ds:[1B208CCh]
  01b2087c d95804          fstp    dword ptr [eax+4]

And that should be with optimization enabled, I didn't start it from the debugger.

But clearly it has some support for using SSE2 when available, because it does use it for zeroing memory:

  01b20884 0f57c0          xorps   xmm0,xmm0
  01b20887 660fd607        movq    mmword ptr [edi],xmm0
  01b2088b 660fd64708      movq    mmword ptr [edi+8],xmm0

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