[LLVMdev] X86InstrFormats.td Question

[David A. Greene]

I'm looking at the instruction formats and I can't grok the comments.  For 
example:

// SSSE3 Instruction Templates:
// 
//   SS38I - SSSE3 instructions with T8 prefix.
//   SS3AI - SSSE3 instructions with TA prefix.
//

Where are these prefix names coming from?  I can't find any mention of them in 
the Intel literature.

Also, there's this curious table:

// Prefix byte classes which are used to indicate to the ad-hoc machine code
// emitter that various prefix bytes are required.
class OpSize { bit hasOpSizePrefix = 1; }
class AdSize { bit hasAdSizePrefix = 1; }
class REX_W  { bit hasREX_WPrefix = 1; }
class LOCK   { bit hasLockPrefix = 1; }
class TB     { bits<4> Prefix = 1; }
class REP    { bits<4> Prefix = 2; }
class D8     { bits<4> Prefix = 3; }
class D9     { bits<4> Prefix = 4; }
class DA     { bits<4> Prefix = 5; }
class DB     { bits<4> Prefix = 6; }
class DC     { bits<4> Prefix = 7; }
class DD     { bits<4> Prefix = 8; }
class DE     { bits<4> Prefix = 9; }
class DF     { bits<4> Prefix = 10; }
class XD     { bits<4> Prefix = 11; }
class XS     { bits<4> Prefix = 12; }
class T8     { bits<4> Prefix = 13; }
class TA     { bits<4> Prefix = 14; }

Are these Prefix values special at all or do they just serve as unique 
identifiers within LLVM?

I'll try adding documentation to this stuff as soon as I figure out what it 
is.

                                       -Dave