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Aucbvax.6972 fa.info-vax utzoo!decvax!ucbvax!info-vax Wed Apr 28 12:01:45 1982 VAX Timing Question >From PRJohnson@MIT-XX Wed Apr 28 11:39:15 1982 Does anyone know why the first of the two following code sequences is slower on both the 780 and the 750?

Sequence 1: addl3 r1,r1,r3 movw r1,r3 bicl2 $0x10000,r3 addl3 r2,r2,r4 movw r2,r4 bicl2 $0x10000,r4

Sequence 2 (a shuffle of sequence 1): addl3 r1,r1,r3 addl3 r2,r2,r4 movw r1,r3 movw r2,r4 bicl2 $0x10000,r3 bicl2 $0x10000,r4

Do the Vaxes pipeline???

The percentage difference is not much on the 780 (about 1.5% speed up), but is larger on the 750 (about 3.5%). Note that the differences still exist if the code sequences are long word aligned, and have NOPs inserted to align all the listed instructions (i.e.: a NOP after each MOVW and each BICL2).

Thanks for any insights.

---Paul Johnson -------

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