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In IR2, a TN represents a value used in a computation. It has a Primitive Type, which determines the set of SCs in which this TN may be found.

TNs are rather like the "infinite registers" in some other compilers: there are SCs for registers and for control stack locations

Most references to TNs occur in VOPs

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The first time I ever heard the term TN was in the era of the CMU Bliss (circa 1975?) compiler work where a great deal of effort was expended getting code generated that made optimal use of registers and stacks given the many curious instruction operands available on the Vax, PDP-11, and PDP-10. The general idea was that every node in the expression tree computed a value and you were going to have to put it someplace on the way to it becoming an operand in for the upstream nodes. So all those were the TN.

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Question: What's the difference between * and *-tn?

Answer: [ As speculated by Christopher Rhodes on #lisp ]

13:38 < Krystof> al-tn refers to AL, always
13:39 < Krystof> eax or something refers to some argument to a VOP; if you want it to actually 
                 *be* the register eax, you need to specify :offset eax-offset in the VOP
13:40 < Krystof> al-tn refers to the register AL always, not the lisp symbol AL :-)

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TN: Technical Note

Pages in this topic: Primitive Type   SC  

Also linked from: Compiler   index   pseudo-atomic   Registers   SB   stack allocation   TNs  

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