🚀 go-pugleaf

In article <???> lindsay@MATHOM.GANDALF.CS.CMU.EDU (Donald Lindsay) writes:
 
}From the press:
 
}"...Digital's engineers isolated the core VAX instruction set,
}including 80% of the most used opcodes and optimized it to the VAX
}9000 gate structure.  The conversion didn't involve reducing - or
}RISCing - the instruction set but more accurately hardwiring it into
}a single-cycle instruction set.  ... The other 20% of complex
}instructions execute with microcode as always..."
 
}If DEC would document exactly what's in that 80%, then VAX compiler
}writers could FINALLY settle the subject of choosing between
}different instruction sequences.

    How hard can it be to figure out?  Write a simple loop:

               MOVL    #BIGNUM,R0
       10$:
               <i-u-t>             ; repeat instruction under test,
                  .                ; say, 100 times
                  :
               <i-u-t>
               SOBGTR  R0,10$

    Anyway, looking at the VAX Arch. Handbook (Chap 10) we find:

        304 instructions (unless they've added some)
        304 * 0.80 = 243 (approx.)
        
        We can probably assume that most of the "Kernel Instruction Set"
   (those instruction required in any implementation--may not be emulated)
   are hardcoded.  That's 175 instructions instructions (less MOVC3, MOVC5,
   LDPCTX, PROBER, PROBEW, REI, SVPCTX, INDEX, POPR, PUSHR, XFC, CALLS, CALLG,
   RET, 6 queue instructions and 7 bitfield instructions) giving 148.  Then
   there are 102 FP instructions (less ACBx (4), POLYx (4) and EMODx (4))
   giving 90.  148 Kernel + 90 FP = 238 instructions (or 78%).  I would
   suspect I'm not off by more than a handfull of instructions in either
   direction.


John Hascall