5 ms·

There's also the fact that for all intents and purposes, the real floating-point unit of any x86 in the last 20 years is the SIMD unit, and legacy x87 instructi

There's also the fact that for all intents and purposes, the real floating-point unit of any x86 in the last 20 years is the SIMD unit, and legacy x87 instructions are emulated on top of that.

whaleofatw2022 4d ago
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)
- ack_complete 4d ago
  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
cogman10 4d ago
I don't believe so. The issue is that x87 is 80bit floats which is awkward. As such, it still requires dedicated hardware. Intel has proposed and abandoned pushing a new x86 architecture [1] which tweaks x86 instructions to fit better with the reality that everything is 64bit now. Part of that proposal was to make x87 work with 64bit floats instead of 80bit floats (which would have allowed it to share the same floating point units as the SIMD instructions). [1] https://www.intel.com/content/www/us/en/developer/articles/technical/envisioning-future-simplified-architecture.html https://www.intel.com/content/www/us/en/developer/articles/t...

There's also the fact that for all intents and purposes, the real floating-point unit of any x86 in the last 20 years is the SIMD unit, and legacy x87 instructions are emulated on top of that.

whaleofatw2022 4d ago

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)

ack_complete 4d ago
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

cogman10 4d ago

I don't believe so. The issue is that x87 is 80bit floats which is awkward. As such, it still requires dedicated hardware. Intel has proposed and abandoned pushing a new x86 architecture [1] which tweaks x86 instructions to fit better with the reality that everything is 64bit now. Part of that proposal was to make x87 work with 64bit floats instead of 80bit floats (which would have allowed it to share the same floating point units as the SIMD instructions). [1] https://www.intel.com/content/www/us/en/developer/articles/technical/envisioning-future-simplified-architecture.html https://www.intel.com/content/www/us/en/developer/articles/t...