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FMA instruction set

January 01, 1970

Wikibooks has a book on the topic of: X86 Assembly/AVX, AVX2, FMA3, FMA4

The FMA instruction set is an extension to the 128 and 256-bit Streaming SIMD Extensions instructions in the x86 microprocessor instruction set to perform fused multiply–add (FMA) operations.[1] There are two variants:

Instructions edit

FMA3 and FMA4 instructions have almost identical functionality, but are not compatible. Both contain fused multiply–add (FMA) instructions for floating-point scalar and SIMD operations, but FMA3 instructions have three operands, while FMA4 ones have four. The FMA operation has the form d = round(a · b + c), where the round function performs a rounding to allow the result to fit within the destination register if there are too many significant bits to fit within the destination.

The four-operand form (FMA4) allows a, b, c and d to be four different registers, while the three-operand form (FMA3) requires that d be the same register as a, b or c. The three-operand form makes the code shorter and the hardware implementation slightly simpler, while the four-operand form provides more programming flexibility.

See XOP instruction set for more discussion of compatibility issues between Intel and AMD.

FMA3 instruction set edit

CPUs with FMA3 edit

  • AMD
    • Piledriver (2012) and newer microarchitectures[3]
      • 2nd gen APUs, "Trinity" (32nm), May 15, 2012
      • 2nd gen "Bulldozer" (bdver2) with Piledriver cores, October 23, 2012
  • Intel

Excerpt from FMA3 edit

Supported commands include

Mnemonic Operation Mnemonic Operation
VFMADD result = + a · b + c VFMADDSUB result = a · b + c  for  i = 1, 3, ...
result = a · b − c  for  i = 0, 2, ...
VFNMADD result = − a · b + c
VFMSUB result = + a · b − c VFMSUBADD result = a · b − c  for  i = 1, 3, ...
result = a · b + c  for  i = 0, 2, ...
VFNMSUB result = − a · b − c
Note
  • VFNMADD is  result = − a · b + c, not  result = − (a · b + c).
  • VFNMSUB generates a −0 for all inputs are zero.

Explicit order of operands is included in the mnemonic using numbers "132", "213", and "231":

Postfix
1		 Operation possible
memory operand		 overwrites
 132 a = a · c + b c (factor) a (other factor)
 213 a = b · a + c c (summand) a (factor)
 231 a = b · c + a c (factor) a (summand)

as well as operand format (packed or scalar) and size (single or double).

Postfix
2		 precision size Postfix
2		 precision size
SS Single 00× 32 bit SD Double 0× 64 bit
PSx 04× 32 bit PDx 2× 64 bit
PSy 08× 32 bit PDy 4× 64 bit
PSz 16× 32 bit PDz 8× 64 bit

This results in

Encoding Mnemonic Operands Operation
VEX.256.66.0F38.W1 98 /r VFMADD132PDy ymm, ymm, ymm/m256 a = a · c + b
VEX.256.66.0F38.W0 98 /r VFMADD132PSy
VEX.128.66.0F38.W1 98 /r VFMADD132PDx xmm, xmm, xmm/m128
VEX.128.66.0F38.W0 98 /r VFMADD132PSx
VEX.LIG.66.0F38.W1 99 /r VFMADD132SD xmm, xmm, xmm/m64
VEX.LIG.66.0F38.W0 99 /r VFMADD132SS xmm, xmm, xmm/m32
VEX.256.66.0F38.W1 A8 /r VFMADD213PDy ymm, ymm, ymm/m256 a = b · a + c
VEX.256.66.0F38.W0 A8 /r VFMADD213PSy
VEX.128.66.0F38.W1 A8 /r VFMADD213PDx xmm, xmm, xmm/m128
VEX.128.66.0F38.W0 A8 /r VFMADD213PSx
VEX.LIG.66.0F38.W1 A9 /r VFMADD213SD xmm, xmm, xmm/m64
VEX.LIG.66.0F38.W0 A9 /r VFMADD213SS xmm, xmm, xmm/m32
VEX.256.66.0F38.W1 B8 /r VFMADD231PDy ymm, ymm, ymm/m256 a = b · c + a
VEX.256.66.0F38.W0 B8 /r VFMADD231PSy
VEX.128.66.0F38.W1 B8 /r VFMADD231PDx xmm, xmm, xmm/m128
VEX.128.66.0F38.W0 B8 /r VFMADD231PSx
VEX.LIG.66.0F38.W1 B9 /r VFMADD231SD xmm, xmm, xmm/m64
VEX.LIG.66.0F38.W0 B9 /r VFMADD231SS xmm, xmm, xmm/m32

FMA4 instruction set edit

CPUs with FMA4 edit

  • AMD
    • "Heavy Equipment" processors
    • Zen: WikiChip's testing shows FMA4 still appears to work (under the conditions of the tests) despite not being officially supported and not even reported by CPUID. This has also been confirmed by Agner Fog.[8] But other tests gave wrong results.[9] AMD Official Web Site FMA4 Support Note ZEN CPUs = AMD ThreadRipper 1900x, R7 Pro 1800, 1700, R5 Pro 1600, 1500, R3 Pro 1300, 1200, R3 2200G, R5 2400G.[10][11][12]
  • Intel
    • Intel has not released CPUs with support for FMA4.

Excerpt from FMA4 edit

Mnemonic (AT&T) Operands Operation
VFMADDPDx xmm, xmm, xmm/m128, xmm/m128 a = b·c + d
VFMADDPDy ymm, ymm, ymm/m256, ymm/m256
VFMADDPSx xmm, xmm, xmm/m128, xmm/m128
VFMADDPSy ymm, ymm, ymm/m256, ymm/m256
VFMADDSD xmm, xmm, xmm/m64, xmm/m64
VFMADDSS xmm, xmm, xmm/m32, xmm/m32

History edit

The incompatibility between Intel's FMA3 and AMD's FMA4 is due to both companies changing plans without coordinating coding details with each other. AMD changed their plans from FMA3 to FMA4 while Intel changed their plans from FMA4 to FMA3 almost at the same time. The history can be summarized as follows:

  • August 2007: AMD announces the SSE5 instruction set, which includes 3-operand FMA instructions. A new coding scheme (DREX) is introduced for allowing instructions to have three operands.[13]
  • April 2008: Intel announces their AVX and FMA instruction sets, including 4-operand FMA instructions. The coding of these instructions uses the new VEX coding scheme,[14] which is more flexible than AMD's DREX scheme.
  • December 2008: Intel changes the specification for their FMA instructions from 4-operand to 3-operand instructions. The VEX coding scheme is still used.[15]
  • May 2009: AMD changes the specification of their FMA instructions from the 3-operand DREX form to the 4-operand VEX form, compatible with the April 2008 Intel specification rather than the December 2008 Intel specification.[16]
  • October 2011: AMD Bulldozer processor supports FMA4.[17]
  • January 2012: AMD announces FMA3 support in future processors codenamed Trinity and Vishera; they are based on the Piledriver architecture.[18]
  • May 2012: AMD Piledriver processor supports both FMA3 and FMA4.[17]
  • June 2013: Intel Haswell processor supports FMA3.[19]
  • February 2017: The first generation of AMD Ryzen processors officially supports FMA3, but not FMA4 according to the CPUID instruction.[2] There has been confusion regarding whether FMA4 was implemented or not on this processor due to errata in the initial patch to the GNU Binutils package that has since been rectified.[20][21] One unconfirmed report of wrong results[9] led to some doubt, but Mysticial (Alexander Yee, developer of y-cruncher) debunked it:[22] FMA4 worked for bit-exact bignum calculations on his Zen 1 system for years, and the one report on Reddit never had any followup investigation to rule out mistakes in the testing software before being widely repeated. The initial Ryzen CPUs could be crashed by a particular sequence of FMA3 instructions, but updated CPU microcode fixes the problem.[23]
  • July 2019: AMD Zen 2 and later Ryzen processors don't support FMA4 at all.[24] They continue to support FMA3. Only Zen 1 and Zen+ have unofficial FMA4 support.

Compiler and assembler support edit

Different compilers provide different levels of support for FMA:

References edit

  1. ^ "FMA3 and FMA4 are not instruction sets, they are individual instructions -- fused multiply add. They could be quite useful depending on how Intel and AMD implement them" Woltmann, George (Prime95). "Intel AVX and GIMPS". mersenneforum.org/index.php. Great Internet Mersenne Prime Search (GIMPS) project. Retrieved 27 July 2011.{{cite web}}: CS1 maint: numeric names: authors list (link)
  2. ^ a b "The microarchitecture of Intel, AMD and VIA CPUs An optimization guide for assembly programmers and compiler makers" (PDF). Retrieved 2017-05-02.
  3. ^ Maffeo, Robin (March 1, 2012). "AMD and the Visual Studio 11 Beta". AMD. Archived from the original on November 9, 2013. Retrieved 2018-11-07.
  4. ^ "CPU-Z - ID : y5z6gq". Retrieved 2022-05-01.
  5. ^ "CPU-Z - ID : kr2mlx". Retrieved 2022-05-01.
  6. ^ "AMD64 Architecture Programmer's Manual Volume 6: 128-Bit and 256-Bit XOP, FMA4 and CVT16 Instructions" (PDF). AMD. May 1, 2009.
  7. ^ "New "Bulldozer" and "Piledriver" Instructions A step forward for high performance software development" (PDF). AMD. October 2012.
  8. ^ "Agner's CPU blog - Test results for AMD Ryzen". 2017-05-02.
  9. ^ a b "Discussion – Ryzen has undocumented support for FMA4". Retrieved 2017-05-10.
  10. ^ "www.amd.com, FMA4 support model list".
  11. ^ "www.amd.com, FMA4 support model list".
  12. ^ "www.amd.com, FMA4 support model list".
  13. ^ . AMD Developer Central. Archived from the original on 2008-01-15. Retrieved 2008-01-28.
  14. ^ "Intel Advanced Vector Extensions Programming Reference" (PDF). Intel. Retrieved 2008-04-05.[permanent dead link]
  15. ^ "Intel Advanced Vector Extensions Programming Reference". Intel. Retrieved 2009-05-06.
  16. ^ "Striking a balance". Dave Christie, AMD Developer blogs. May 6, 2009. Archived from the original on July 8, 2012. Retrieved 2018-11-07.
  17. ^ a b "New Bulldozer and Piledriver Instructions" (PDF). AMD. Retrieved 25 July 2013.
  18. ^ "Software Optimization Guide for AMD Family 15h Processors" (PDF). AMD. Retrieved 19 April 2012.
  19. ^ "Intel Architecture Instruction Set Extensions Programming Reference" (PDF). Intel. Retrieved 25 July 2013.
  20. ^ Gopalasubramanian, Ganesh (2015-03-10). "[PATCH] add znver1 processor". Retrieved 2022-05-01.
  21. ^ Pawar, Amit (2015-08-07). "[PATCH] Remove CpuFMA4 from Znver1 CPU Flags". Retrieved 2022-05-01.
  22. ^ . 2019-07-16. Archived from the original on 2019-08-22. Retrieved 2023-09-01.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  23. ^ "AMD Ryzen Machine Crashes to a Sequence of FMA3 Instructions". 16 March 2017. Retrieved 2017-09-10.
  24. ^ "Stack Overflow comment by Mysticial". 2019-07-16. Retrieved 2023-09-01.
  25. ^ a b Latif, Lawrence (Nov 14, 2011). . The Inquirer. Archived from the original on November 17, 2011.{{cite web}}: CS1 maint: unfit URL (link)
  26. ^ "FMA4 Intrinsics Added for Visual Studio 2010 SP1". 4 February 2013.
  27. ^ . Archived from the original on 2016-06-23. Retrieved 2013-07-24.
  28. ^ "LLVM 3.1 Release Notes".
  29. ^ "Enable detection of AVX and AVX2 support through CPUID". LLVM. 2012-04-26.

January 01, 1970
instruction, wikibooks, book, topic, assembly, avx2, fma3, fma4, extension, streaming, simd, extensions, instructions, microprocessor, instruction, perform, fused, multiply, operations, there, variants, fma4, supported, processors, starting, with, bulldozer, a. Wikibooks has a book on the topic of X86 Assembly AVX AVX2 FMA3 FMA4 The FMA instruction set is an extension to the 128 and 256 bit Streaming SIMD Extensions instructions in the x86 microprocessor instruction set to perform fused multiply add FMA operations 1 There are two variants FMA4 is supported in AMD processors starting with the Bulldozer architecture FMA4 was performed in hardware before FMA3 was Support for FMA4 has been removed since Zen 1 2 FMA3 is supported in AMD processors starting with the Piledriver architecture and Intel starting with Haswell processors and Broadwell processors since 2014 Contents 1 Instructions 2 FMA3 instruction set 2 1 CPUs with FMA3 2 2 Excerpt from FMA3 3 FMA4 instruction set 3 1 CPUs with FMA4 3 2 Excerpt from FMA4 4 History 5 Compiler and assembler support 6 ReferencesInstructions editFMA3 and FMA4 instructions have almost identical functionality but are not compatible Both contain fused multiply add FMA instructions for floating point scalar and SIMD operations but FMA3 instructions have three operands while FMA4 ones have four The FMA operation has the form d round a b c where the round function performs a rounding to allow the result to fit within the destination register if there are too many significant bits to fit within the destination The four operand form FMA4 allows a b c and d to be four different registers while the three operand form FMA3 requires that d be the same register as a b or c The three operand form makes the code shorter and the hardware implementation slightly simpler while the four operand form provides more programming flexibility See XOP instruction set for more discussion of compatibility issues between Intel and AMD FMA3 instruction set editCPUs with FMA3 edit AMD Piledriver 2012 and newer microarchitectures 3 2nd gen APUs Trinity 32nm May 15 2012 2nd gen Bulldozer bdver2 with Piledriver cores October 23 2012 Intel Haswell 2013 and newer processors except Pentiums and Celerons 4 5 Excerpt from FMA3 edit Supported commands include Mnemonic Operation Mnemonic Operation VFMADD result a b c VFMADDSUB result a b c for i 1 3 result a b c for i 0 2 VFNMADD result a b c VFMSUB result a b c VFMSUBADD result a b c for i 1 3 result a b c for i 0 2 VFNMSUB result a b c Note VFNMADD is result a b c not result a b c VFNMSUB generates a 0 for all inputs are zero Explicit order of operands is included in the mnemonic using numbers 132 213 and 231 Postfix1 Operation possiblememory operand overwrites 132 a a c b c factor a other factor 213 a b a c c summand a factor 231 a b c a c factor a summand as well as operand format packed or scalar and size single or double Postfix2 precision size Postfix2 precision size SS Single 00 32 bit SD Double 0 64 bit PSx 0 4 32 bit PDx 2 64 bit PSy 0 8 32 bit PDy 4 64 bit PSz 16 32 bit PDz 8 64 bit This results in Encoding Mnemonic Operands Operation VEX 256 66 0F38 W1 98 r VFMADD132PDy ymm ymm ymm m256 a a c b VEX 256 66 0F38 W0 98 r VFMADD132PSy VEX 128 66 0F38 W1 98 r VFMADD132PDx xmm xmm xmm m128 VEX 128 66 0F38 W0 98 r VFMADD132PSx VEX LIG 66 0F38 W1 99 r VFMADD132SD xmm xmm xmm m64 VEX LIG 66 0F38 W0 99 r VFMADD132SS xmm xmm xmm m32 VEX 256 66 0F38 W1 A8 r VFMADD213PDy ymm ymm ymm m256 a b a c VEX 256 66 0F38 W0 A8 r VFMADD213PSy VEX 128 66 0F38 W1 A8 r VFMADD213PDx xmm xmm xmm m128 VEX 128 66 0F38 W0 A8 r VFMADD213PSx VEX LIG 66 0F38 W1 A9 r VFMADD213SD xmm xmm xmm m64 VEX LIG 66 0F38 W0 A9 r VFMADD213SS xmm xmm xmm m32 VEX 256 66 0F38 W1 B8 r VFMADD231PDy ymm ymm ymm m256 a b c a VEX 256 66 0F38 W0 B8 r VFMADD231PSy VEX 128 66 0F38 W1 B8 r VFMADD231PDx xmm xmm xmm m128 VEX 128 66 0F38 W0 B8 r VFMADD231PSx VEX LIG 66 0F38 W1 B9 r VFMADD231SD xmm xmm xmm m64 VEX LIG 66 0F38 W0 B9 r VFMADD231SS xmm xmm xmm m32FMA4 instruction set editCPUs with FMA4 edit AMD Heavy Equipment processors Bulldozer based processors October 12 2011 6 Piledriver based processors 7 Steamroller based processors Excavator based processors including v2 Zen WikiChip s testing shows FMA4 still appears to work under the conditions of the tests despite not being officially supported and not even reported by CPUID This has also been confirmed by Agner Fog 8 But other tests gave wrong results 9 AMD Official Web Site FMA4 Support Note ZEN CPUs AMD ThreadRipper 1900x R7 Pro 1800 1700 R5 Pro 1600 1500 R3 Pro 1300 1200 R3 2200G R5 2400G 10 11 12 Intel Intel has not released CPUs with support for FMA4 Excerpt from FMA4 edit Mnemonic AT amp T Operands Operation VFMADDPDx xmm xmm xmm m128 xmm m128 a b c d VFMADDPDy ymm ymm ymm m256 ymm m256 VFMADDPSx xmm xmm xmm m128 xmm m128 VFMADDPSy ymm ymm ymm m256 ymm m256 VFMADDSD xmm xmm xmm m64 xmm m64 VFMADDSS xmm xmm xmm m32 xmm m32History editThe incompatibility between Intel s FMA3 and AMD s FMA4 is due to both companies changing plans without coordinating coding details with each other AMD changed their plans from FMA3 to FMA4 while Intel changed their plans from FMA4 to FMA3 almost at the same time The history can be summarized as follows August 2007 AMD announces the SSE5 instruction set which includes 3 operand FMA instructions A new coding scheme DREX is introduced for allowing instructions to have three operands 13 April 2008 Intel announces their AVX and FMA instruction sets including 4 operand FMA instructions The coding of these instructions uses the new VEX coding scheme 14 which is more flexible than AMD s DREX scheme December 2008 Intel changes the specification for their FMA instructions from 4 operand to 3 operand instructions The VEX coding scheme is still used 15 May 2009 AMD changes the specification of their FMA instructions from the 3 operand DREX form to the 4 operand VEX form compatible with the April 2008 Intel specification rather than the December 2008 Intel specification 16 October 2011 AMD Bulldozer processor supports FMA4 17 January 2012 AMD announces FMA3 support in future processors codenamed Trinity and Vishera they are based on the Piledriver architecture 18 May 2012 AMD Piledriver processor supports both FMA3 and FMA4 17 June 2013 Intel Haswell processor supports FMA3 19 February 2017 The first generation of AMD Ryzen processors officially supports FMA3 but not FMA4 according to the CPUID instruction 2 There has been confusion regarding whether FMA4 was implemented or not on this processor due to errata in the initial patch to the GNU Binutils package that has since been rectified 20 21 One unconfirmed report of wrong results 9 led to some doubt but Mysticial Alexander Yee developer of y cruncher debunked it 22 FMA4 worked for bit exact bignum calculations on his Zen 1 system for years and the one report on Reddit never had any followup investigation to rule out mistakes in the testing software before being widely repeated The initial Ryzen CPUs could be crashed by a particular sequence of FMA3 instructions but updated CPU microcode fixes the problem 23 July 2019 AMD Zen 2 and later Ryzen processors don t support FMA4 at all 24 They continue to support FMA3 Only Zen 1 and Zen have unofficial FMA4 support Compiler and assembler support editDifferent compilers provide different levels of support for FMA GCC supports FMA4 with mfma4 since version 4 5 0 25 and FMA3 with mfma since version 4 7 0 Microsoft Visual C 2010 SP1 supports FMA4 instructions 26 Microsoft Visual C 2012 supports FMA3 instructions if the processor also supports AVX2 instruction set extension Microsoft Visual C since VC 2013 PathScale supports FMA4 with mfma 27 LLVM 3 1 adds FMA4 support 28 along with preliminary FMA3 support 29 Open64 5 0 adds limited support Intel compilers support only FMA3 instructions 25 NASM supports FMA3 instructions since version 2 03 and FMA4 instructions since 2 06 FASM supports both FMA3 and FMA4 instructions References edit FMA3 and FMA4 are not instruction sets they are individual instructions fused multiply add They could be quite useful depending on how Intel and AMD implement them Woltmann George Prime95 Intel AVX and GIMPS mersenneforum org index php Great Internet Mersenne Prime Search GIMPS project Retrieved 27 July 2011 a href Template Cite web html title Template Cite web cite web a CS1 maint numeric names authors list link a b The microarchitecture of Intel AMD and VIA CPUs An optimization guide for assembly programmers and compiler makers PDF Retrieved 2017 05 02 Maffeo Robin March 1 2012 AMD and the Visual Studio 11 Beta AMD Archived from the original on November 9 2013 Retrieved 2018 11 07 CPU Z ID y5z6gq Retrieved 2022 05 01 CPU Z ID kr2mlx Retrieved 2022 05 01 AMD64 Architecture Programmer s Manual Volume 6 128 Bit and 256 Bit XOP FMA4 and CVT16 Instructions PDF AMD May 1 2009 New Bulldozer and Piledriver Instructions A step forward for high performance software development PDF AMD October 2012 Agner s CPU blog Test results for AMD Ryzen 2017 05 02 a b Discussion Ryzen has undocumented support for FMA4 Retrieved 2017 05 10 www amd com FMA4 support model list www amd com FMA4 support model list www amd com FMA4 support model list 128 Bit SSE5 Instruction Set AMD Developer Central Archived from the original on 2008 01 15 Retrieved 2008 01 28 Intel Advanced Vector Extensions Programming Reference PDF Intel Retrieved 2008 04 05 permanent dead link Intel Advanced Vector Extensions Programming Reference Intel Retrieved 2009 05 06 Striking a balance Dave Christie AMD Developer blogs May 6 2009 Archived from the original on July 8 2012 Retrieved 2018 11 07 a b New Bulldozer and Piledriver Instructions PDF AMD Retrieved 25 July 2013 Software Optimization Guide for AMD Family 15h Processors PDF AMD Retrieved 19 April 2012 Intel Architecture Instruction Set Extensions Programming Reference PDF Intel Retrieved 25 July 2013 Gopalasubramanian Ganesh 2015 03 10 PATCH add znver1 processor Retrieved 2022 05 01 Pawar Amit 2015 08 07 PATCH Remove CpuFMA4 from Znver1 CPU Flags Retrieved 2022 05 01 Stack Overflow comment by Mysticial 2019 07 16 Archived from the original on 2019 08 22 Retrieved 2023 09 01 a href Template Cite web html title Template Cite web cite web a CS1 maint bot original URL status unknown link AMD Ryzen Machine Crashes to a Sequence of FMA3 Instructions 16 March 2017 Retrieved 2017 09 10 Stack Overflow comment by Mysticial 2019 07 16 Retrieved 2023 09 01 a b Latif Lawrence Nov 14 2011 AMD Bulldozer only FMA4 and XOP instructions are supported by GCC Intel still mute The Inquirer Archived from the original on November 17 2011 a href Template Cite web html title Template Cite web cite web a CS1 maint unfit URL link FMA4 Intrinsics Added for Visual Studio 2010 SP1 4 February 2013 EKOPath man doc Archived from the original on 2016 06 23 Retrieved 2013 07 24 LLVM 3 1 Release Notes Enable detection of AVX and AVX2 support through CPUID LLVM 2012 04 26 Retrieved from https en wikipedia org w index php title FMA instruction set amp oldid 1215967821, wikipedia, wiki, book, books, library,

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