This one might be more relevant to the "oldtimers" or programmers, but I was just wondering how widespread the use of MMX instructions became/is? I know they were limited to integer applications and actually usurped registers from X87(making it difficult to use MMX along side any FP work), but have these instructions managed to wiggle into the default codepath (to any meaningful degree) in any widely used compiler or have they more faded off into history?
Just wondering about MMX
- Thread starter nismotigerwvu
- Start date
I kind of figured that they were all but gone in X64 (why would AMD have placed any emphasis on them anyways), but I was more curious as to how widely they were incorporated at their peak more or less.
- Dec 11, 1999
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I don't think compiler makers got caught up to vectorization very much until MMX was already out of the picture. I see that by 2003 both Intel and AMD had SSE2 in their processors. Meanwhile, GCC wasn't even working on vectorization until 2004, by which point they focused on sse/sse2. It looks like they still don't do MMX vectorization automatically.
Of course, GCC is a Free compiler. I'm sure Intel's compiler had some sort of MMX support at some point. I'm not sure about Microsoft, but I gather they weren't doing much either.
And by the way, x87 isn't gone in X64. I've used it. Sometimes you just need 80-bit floating point numbers.
Of course, GCC is a Free compiler. I'm sure Intel's compiler had some sort of MMX support at some point. I'm not sure about Microsoft, but I gather they weren't doing much either.
And by the way, x87 isn't gone in X64. I've used it. Sometimes you just need 80-bit floating point numbers.
And by the way, x87 isn't gone in X64. I've used it. Sometimes you just need 80-bit floating point numbers.
I think he meant that almost nobody uses them rather than those entities not existing in 64-bit mode.
I don't think compiler makers got caught up to vectorization very much until MMX was already out of the picture. I see that by 2003 both Intel and AMD had SSE2 in their processors. Meanwhile, GCC wasn't even working on vectorization until 2004, by which point they focused on sse/sse2. It looks like they still don't do MMX vectorization automatically.
Of course, GCC is a Free compiler. I'm sure Intel's compiler had some sort of MMX support at some point. I'm not sure about Microsoft, but I gather they weren't doing much either.
And by the way, x87 isn't gone in X64. I've used it. Sometimes you just need 80-bit floating point numbers.
Ahh, this is exactly what I was looking for, thanks.
your slide looks very outdated and about OS support, not about ISA or hardware support
where do they say that in the specs?
http://support.amd.com/us/Processor_TechDocs/26569_APM_v5.pdf
where do they say that in the specs?
http://support.amd.com/us/Processor_TechDocs/26569_APM_v5.pdf
ShintaiDK
Lifer
- Apr 22, 2012
- 20,378
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Its actually from AMD by Mike Wall due the launch of AMD64.
http://web.archive.org/web/20030916...wnloadableAssets/AMD_TechEdEMEA2003_Final.pdf
And yes, its in combination with Windows.
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mmm, this is a *2003* slide about supposed Windows ABI limitations at the time, isn't it?
for more recent data look at up to date material like:
http://support.amd.com/us/Processor_TechDocs/24592_APM_v1.pdf
see 6.1.3 page 280 for example :
"
x87 floating-point instructions can be executed in any of the architectures operating modes. Existing
x87 binary programs run in legacy and compatibility modes without modification. The support
provided by the AMD64 architecture for such binaries is identical to that provided by legacy x86
architectures.x87 binary programs run in legacy and compatibility modes without modification. The support
provided by the AMD64 architecture for such binaries is identical to that provided by legacy x86
"
ShintaiDK
Lifer
- Apr 22, 2012
- 20,378
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Very unlikely. Considering how many transistors made up an entire CPU back when MMX was introduced, and how many are in a processor now, it's probably fractions of square mm in savings.
ShintaiDK
Lifer
- Apr 22, 2012
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they are only mentioned as deprecated for the assembler, btw your quote is very misleading out of context (on purpose?), 99.99%+ of the x87 code is probably user-mode compiler generated code and thus for most practical purposes x87 code is fully supported on 64-bit Windows in other words your "You can use x87 in Linux for example, but not in Windows." statement is plain wrong
btw I know it *first hand* since I routinely use x87 code in my 64-bit code on Windows 7 (for example for transcendentals)
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ShintaiDK
Lifer
- Apr 22, 2012
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sorry, to be more clear these two *entire* statements of yours are plain wrong:
"You could also simplify it with that MMX, 3Dnow and x87 aint supported in long mode arcording to AMDs AMD64 specs."
"You can use x87 in Linux for example, but not in Windows. In Windows MMX, 3DNow! and x87 is unavaliable from long mode."
"You could also simplify it with that MMX, 3Dnow and x87 aint supported in long mode arcording to AMDs AMD64 specs."
"You can use x87 in Linux for example, but not in Windows. In Windows MMX, 3DNow! and x87 is unavaliable from long mode."
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cytg111
Lifer
- Mar 17, 2008
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support.amd.com/us/Processor_TechDocs/26569_APM_v5.pdf
says on page 215
"...The x87 floating-point
instructions are used in legacy floating-point applications..."
and then
"...The x87 instructions can be used in legacy mode or long mode. Their use in long mode is available if
the following CPUID function bit is set to 1:Long Mode, indicated by bit 29 of CPUID function 8000_0001h. ..."
For what it is worth.
says on page 215
"...The x87 floating-point
instructions are used in legacy floating-point applications..."
and then
"...The x87 instructions can be used in legacy mode or long mode. Their use in long mode is available if
the following CPUID function bit is set to 1:Long Mode, indicated by bit 29 of CPUID function 8000_0001h. ..."
For what it is worth.
good catch, though it's not very clear since they don't say if it's bit #29 of EAX,EBX,ECX or EDX
http://support.amd.com/us/Embedded_TechDocs/25481.pdf
this looks like an AMD only flag, maybe due to the missing support for x87 in long mode on early chips, this will explain the obsolete slide posted by someone above
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